Cont. part a
29-24 VHF TUNER
For Black-and- white Television Receiver
Circuit Description
This vhf tuner selects the desired vhf frequency channel, amplifies composite video signals in the frequency channel selected, and converts the signal frequencies to the 45.75-MHz picture intermediate frequency and the 41.25-MHz sound intermediate frequency used in television receivers. When used with a uhf tuner, the vhf tuner is operated as a two-stage broadband rf amplifier tuned to 44 MHz (center frequency of the if band) and is essentially a pre-if amplifier for the television receiver. In each mode of operation, the tuner has a band pass that is broad enough to pass all the video information (including synchronizing and equalizing pulses) and the sound information super imposed on the video and sound carrier frequencies and has sufficient selectivity to assure adequate adjacent-channel and image-frequency rejection. The +140 volts used as the B+ supply for the vhf tuner is obtained from the low-voltage power supply of the receiver. The heaters of the tubes in the circuit are connected in series with those of other tubes in the receiver, and power for the series heater string is obtained directly from the input ac power line.
The antenna used with the vhf tuner may be either a 75-ohm mono pole, as used with portable receivers, or a balanced 300-ohm antenna. A balanced 300-ohm antenna system can be matched to the unbalanced 75-ohm tuner input by means of the antenna-matching balun T1. A 13 position channel selector, which consists of several wafer-switch sections (S1 through S4 ) mounted on a common shaft, establishes the operating frequency of the tuner for each of the vhf channels 2 through 13 or adapts the vhf tuner for operation with a uhf tuner. With S4 set to any of the channel positions 2 through 13, the selected-channel signal from the vhf antenna is coupled through contacts U and 2 of SJB and input transformer T2 to the rf amplifier, and the input lead from the uhf tuner is not connected to the vhf circuit.
The vhf input signals are amplified by the 3GK5 high-mu frame grid triode used in the rf amplifier stage. The S3 section of the channel selector connects the appropriate combination of the inductors L5 through L15 into the grid circuit of the rf amplifier to tune this stage to the desired frequency channel. The age bias voltage applied to the control grid of the 3GK5 triode automatically controls the gain of the rf stage. The bias voltage, which varies directly with the amplitude of the received signal, is derived by a keyed age amplifier in the television receiver.
The output of the rf amplifier is coupled through a resonant impedance network to the control grid of ...
---------------
Parts List
C1, C2=82 pF, ±6%, dual disc, ceramic, 500 V, N750
C3, C4, C5, C15, C16=1000 pF, feedthrough, 500 V
Ce=12 pFt 5%, ceramic, 500 V, N750
C7=20 pF, ±6%, feed through, 600 V, N470 C«=0.56 pF, ±5%, headed lead, 500 V C»=100 pF, ceramic, 500 V, N1500 C1o=0.22 uF, ceramic, 500 V C1i=0.82 pF, headed lead, 600 V Cu=82 pF, ±6%, feed through, 600 V, N760 C1a=8 pF, ceramic, 500 V Cu=10 pF, ±6%, radial leads, ceramic, 500 V, N830 GIMMICK=Trimmer-capacitor plate Li, Is, Ls=RF coils : with two 82-picofarad capacitors, forms high-pass filter (antenna input network), RCA Stock No. 114458 or equiv.
Lt=RF amplifier grid coil, part of S1 assembly Ls through Lis=RF-amplifier tuning coils, part of Ss assembly Li»=Mixer grid coil, part of S2 assembly LiT=Interstage coupling coil for rf amplifier and mixer, part of S2 assembly Lis through Lz»=Mixer tuning coils, part of S2 assembly Lao=Variable rf coil ; mixer plate tuning adjustment RCA stock No. 112909 or equiv.
L»=RF choke L32=Variable rf coil ; local oscillator tuning adjustment for channel 13 Lra through Li43=Local oscillator tuning coils (variable coil Ls» is tuning adjustment for channel 6), part of S1 assembly L«=Variable rf coil ; fine tuning control ; RCA Stock No. 113323. or equiv.
Ri=4700 ohms, 1 watt R2=5600 ohms, 0.5 watt Rs=47000 ohms, 0.6 watt Ri:=0.1 megohm, 0.5 watt Re, R7=10000 ohms, 0.5 watt R», R10=1000 ohms, 0.5 watt Rs=2200 ohms, 0.5 watt R»=6800 ohms, 0.5 watt Si=Local-oscillator section of channel-selector switch stator assembly, RCA Stock No. 114462 or equiv., includes local oscillator tuning coils L33 through L4S S2=Mixer section of channel-selector switch ; stator assembly, RCA Stock No. 114461 or equiv., includes mixer tuning coils Ls, La, and Lis through L29 Ss=RF amplifier section of channel-selector switch stator assembly, RCA Stock No. 114460 or equiv., includes rf-amplifier tuning coils L* and Lr through L17 S<=VHF-UHF function se lector ; two-section switch ganged with channel se lectors. Si, S2, and Ss;
RCA Stock No. 114185 or equiv.
T1=Antenna-matching balun ; matches 300-ohm balanced antenna-lead line to 75-ohm unbalanced receiver-input line ; RCA Stock No. 111973 or equiv.
T2=Antenna transformer; RCA Stock No. 113195 or equiv.
Z1, Z2=Resistance-capacitance network (capristor), RCA Stock No. 109956 or equiv.
Notes: 1. All switches are ganged together on same shaft and are shown with shaft in channel 13 position.
2. Voltages shown are obtained with no signal input.
3. For dc voltage and heater supply, see circuit 29-28, page 725.
4. See additional notes on page 712.
-----------------------
... the 6KZ8 pentode section used in the mixer stage. Section S2 of the ganged channel selector selects the proper combination of the inductors Lis through L» to tune the mixer input circuit to the same operating frequency as that of the rf amplifier. A signal from the plate of the 6KZ8 triode section used in the local-oscillator stage is also applied to the input circuit of the mixer. Section Sj of the channel selector connects the right combination of the inductors L33 through Lu3 into the oscillator resonant circuit to maintain the operating frequency of the oscillator at 45.75 MHz above the video carrier frequency (41.25 MHz above the sound carrier frequency) of the vhf channel selected by the tuner. Inductor LH in the series-resonant feedback circuit of the oscillator is the fine tuning adjustment for the vhf tuner.
This adjustment assures that the oscillator frequency accurately tracks the input tuning in each channel.
The signals from the rf amplifier and the local oscillator are heterodyned in the mixer stage to produce the 45.75-MHz amplitude modulated and 41.25-MHz frequency-modulated difference frequencies used as the picture and sound inter mediate frequencies, respectively, in the television receiver. The picture and sound if signals are coupled from the plate of the mixer to the if stages of the receiver.
When the multiple-section channel selector is rotated to the U position (for uhf operation), a connection from the B+ line of the vhf tuner through a 5600-ohm dropping resistor R2, contacts 4 and 10 of Su, and a 4700-ohm dropping resistor Rt provides the B+ voltage for the uhf tuner. In addition, transformer T2, which provides the input to the rf amplifier, is connected through contacts 2 and 13 of SJB to the output of the uhf tuner, and the signal from the vhf antenna is shorted to ground through contacts U and 12 of Sn.
The input to the rf amplifier is then the amplitude-modulated 45.75-MHz picture if and frequency-modulated 41.25-MHz sound if signals from the uhf tuner.
In the U positions, switch sections S3 and S2 select the tuning inductors required for operation of the rf amplifier and mixer stages as broadband 44-MHz amplifiers, and section S1 disables the oscillator stage by connection of the oscillator control grid directly to ground through switch contacts 2 and U.
With these changes, the vhf tuner essentially becomes a broadband 44 MHz amplifier which provides two stages of amplification of the picture and sound if signals ahead of the receiver main if strip.
29-25 VIDEO-IF AMPLIFIERS AND SOUND-CHANNEL CIRCUITS
For Black-and-White Television Receiver
Circuit Description
These circuit stages are typical of those used in the if and audio channels of any intercarrier type of black-and-white television receiver.
The over-all circuit operates from a dc supply of +150 volts obtained from the receiver low-voltage (B + ) dc power supply. The heaters of the tubes in the circuit are connected in series with those of tubes in other sections of the receiver. Operating power for the series heater string is obtained directly from the 117-volt ac power line.
The input from the vhf tuner consists of amplitude-modulated 45.75 MHz picture if signals and frequency-modulated 41.25-MHz sound if signals. This composite input is coupled by a broadly tuned bandpass filter network to the control grid of the 4JD6 remote-cutoff pentode used in the first picture if amplifier. A dc bias voltage proportional to the in put signal from the age amplifier is also applied to the control-grid circuit to provide automatic gain control of this stage. The output of the first picture if amplifier is coupled by the single-tuned transformer T1 to the control grid of the 4JC6A pentode used in the second picture if amplifier. The double-tuned trans former T. couples the output of this stage to the video detector (CR1 and associated components). The in put filter network and picture if transformers T1 and T2 are stagger tuned to obtain the broad response for the if amplifiers required to as sure adequate passage of both the 45.75-MHz video and 41.25-MHz sound if signals.
The video detector demodulates the 45.75-MHz picture if signal, and the resultant video signal is coupled through inductors L5 and Lr and the lower winding of transformer T3 to the video amplifier (shown in circuit 29-27). The video detector also operates as a second mixer circuit.
The 45.75-MHz picture if signal and the 41.25 sound if signal are heterodyned to produce a second sound if carrier of 4.5 MHz. This 4.5-MHz second sound if carrier is still frequency-modulated by the audio components contained in the original rf signal input at the receiver antenna.
----------------------
Parts List
C1, Cb=470 pF, ceramic, BOO V Cs, Ct=0.001 hT, ceramic BOO V Ca=7 pF, ceramic BOO V, N160 C»=2 pF, ceramic, 600 V, NPO C»=66 pF, ±6%, ceramic, BOO V, N7B0 C*=660 pF, ceramic, 500 V Cb=18 pF, 5%, ceramic, 600 V, N220 C1o=6 pF, ceramic, BOO V Cu=10 pF, ceramic, 500 V, NPO C12=39 pF, ceramic, 600 V, N150 C1s=68 pF, ceramic, 500 V, N750 Cw, C1o=0.01 uF, ceramic, 600 V C1s, Cn=12 pF, part of T» C1e, C1s=0.0022 uF, ceramic, 600 V Cso=I0 pF, part of Ts Ca=680 pF, ceramic, 600 V C2a=0.047 uF, paper, 200 V Cz3=0.01 uF, ceramic, 500 V C»=0.0066 uF, ceramic, 600 V CRi=Video detector, crystal diode, RCA Stock No.
112524 or equiv.
Li=RF coil, RCA Stock No.
114315 or equiv.
L2=RF coil, RCA Stock No.
114314 or equiv.
Ls=RF coil, 47.25-MHz trap RCA Stock No. 113097 or equiv.
lu=:RF coil, RCA Stock No.
113097 or equiv.
L5=Video-detector peaking coil, 36 uH, RCA Stock No. 109758 or equiv.
L7=Filter choke (reactor), 2.7 uH, RCA Stock No. 107463 or equiv.
R1=3300 ohms, 0.5 watt Rs=1000 ohms, 0.6 watt R»=39 ohms, ±5%,
0.6 watt R«=4700 ohms, ±5%,
0.5 watt Rs=1500 ohms, 1 watt
Ra=100 ohms, 0.5 watt
R7=470 ohms, 0.5 watt
Rs=3000 ohms, ±5%, 0.5 watt
R»=820 ohms, 0.5 watt
Rio=82000 ohms, 0.5 watt
Ru=15000 ohms, 1 watt
Ri2=560 ohms, 0.5 watt
Ria=470 ohms, 0.5 watt
Rii-0.47 megohm, 0.5 watt
Ris=0.39 megohm, 0.5 watt
Rie=Volume control, potentiometer, 1 megohm
Rn=180 ohms, 0.5 watt
Ti=First pix if transformer, RCA Stock No. 109158 or equiv.
T2=Second pix if trans former, RCA Stock No.
114317 or equiv.
T3=Sound take-off trans former, 4.5-MHz, RCA Stock No. 114489 or equiv.
T1=Sound if transformer (includes primary and secondary capacitors).
Notes: 1. Voltages shown are obtained with no signal input.
2. For dc voltage and heater supply, see circuit 29-28, page 725.
3. See additional notes on page 712.
RCA Stock No. 104137 or equiv.
Ts=Sound detector resonant circuit (includes 10-pF capacitor), RCA Stock No. 109948 or equiv.
To=Audio output trans former, matches speaker voice-coil impedance to tube plate load, RCA Stock No. 114490 or equiv.
----------
The sound-takeoff transformer T3, which forms a selective load impedance for the detector circuit at 4.5 MHz, couples the 4.5-MHz sound if signal to the control grid of the pentode section of a 6GH8A triode pentode used in the sound if amplifier. The amplified if signal from this stage is coupled by the doubled tuned 4.5-MHz transformer Tt to the 6HZ6 audio detector-amplifier stage.
This stage demodulates the 4.5-MHz sound if signal and amplifies the resultant audio signal voltage. The +250 volts used as the plate supply for the 6HZ6 is obtained from the horizontal output stage (shown in circuit 29-27 of the receiver.
The audio-signal power required to drive the speaker is developed by a 12FX5 pentode used in a single ended audio output stage. The audio signal voltage from the plate of the audio detector-amplifier is amplified by the 12FX5 and coupled by trans former To to the voice coil of the speaker. The volume-control potentiometer R10 in the input circuit of the output stage provides manual adjustment of the sound level from the speaker.
---------------------
29-26 VIDEO, AGC, AND SYNC AMPLIFIERS
For Black-and-White TV Receiver
Circuit Description
This circuit shows video, age, and sync amplifiers for a black-and white television receiver. The video and sync amplifiers operate from a plate supply (B + ) voltage of 150 volts obtained from the receiver low voltage power supply. The plate sup ply voltage for the age amplifier is a positive keying pulse from the high-voltage transformer in the receiver. The heaters of the three tubes are connected in series with those of tubes in other sections of the receiver. Operating power for the series heater string is obtained directly from the ac power line.
In the video amplifier, the pentode section of an 11LQ8 triode-pentode provides the required amplification of the video signal. The video signal is coupled from the video detector to the control grid of the video amplifier. The output from the voltage divider in the plate circuit of this stage is applied to the cathode of the picture tube to intensity-modulate the electron beam during its vertical and horizontal scanning of the picture-tube screen.
The contrast control adjusts both the amplitude of the video output and the dc potential at the cathode of the picture tube to control picture contrast. The voltage-divider net work in the plate circuit of the video amplifier is interconnected with an other voltage-divider network. This second network includes the bright ness control and the width control in the screen-grid circuit of the receiver horizontal-output tube (shown in circuit 29-27). The brightness control adjusts the cathode bias on the picture tube to control the intensity of the screen display.
An output from the video amplifier is also applied to the control grid of the 11LQ8 triode section used ...
---------------
Notes: 1. Voltages shown are obtained with no signal input.
2. For dc voltage and heater supply, see circuit 29-28, page 725.
3. See additional notes on page 712.
Parts List
C1=6 uF, electrolytic, 150 V
Cs=0.16 uF, paper, 200 V
Ca=0.033, paper, 200 V
C1=0.0047, ceramic, 500 V
C»=0.1 uF, paper, 200 V
Ca=470 pF, ceramic, 600 V
C»=100 pF, ceramic, 500 V, N1600
L1=Video-amplifier peaking coil, 18 uH, RCA Stock No. 109946 or equiv.
R1=18000 ohms, 0.5 watt
R2=330 ohms, 0.5 watt Ra=1500 ohms, 0.5 watt
R4=Contrast control, potentiometer, 4000 ohms, 3 watts
R5=1 megohm, 0.5 watt
Re=10 ohms, ±5%, 0.5 watt
R7=22000 ohms, 0.5 watt
Rs=0.27 megohm, 0.5 watt
R», Rio, Rio=27000 ohms,
0.5 watt Rn=27000 ohms, 1 watt Ri2=18000 ohms, 0.5 watt Ri3=Brightness control, potentiometer, 0.1 megohm Rii, Ri?=0.82 megohm,
0.5 watt Ri5=l megohm, 0.5 watt Rie, R2i=0.68 megohm,
0.5 watt Ris=3300 ohms, 0.5 watt Ri»=8.2 megohms, 0.5 watt R22=5.2 megohms, 0.5 watt R23=33000 ohms, 0.5 watt R 4=15000 ohms, watt
----------------------
... in a keyed-age amplifier stage. The operation of the age amplifier is gated (keyed) by a positive pulse from the high-voltage power trans former (shown in circuit 29-27).
This 450-volt keying pulse, which is synchronized with the video signal, overcomes the bias provided by the 150 volts applied to the cathode circuit and serves as the plate supply voltage for the age amplifier. Portions of the video signal that occur coincident with the keying pulse are amplified by the age stage. A 0.1 microfarad capacitor C3 and a 0.82 megohm resistor Ru in the plate circuit of this stage filter out the pulsating components to obtain a negative dc voltage proportional to the video signal and thus to the rf input at the receiver antenna. The negative voltage developed in the plate circuit of the stage is applied as age bias to the first picture if amplifier and to the rf amplifier in the vhf tuner.
Synchronizing pulses are included in the video signals trans mitted by a television broadcast station to provide timing information required for synchronization of the transmitter and receiver scanning systems. The sync amplifier, or separator, separates and amplifies the synchronizing pulses contained in the composite video signal it receives from the plate circuit of the video amplifier. The circuit uses the triode section of a 6GH8A triode pentode to develop the synchronizing pulses for the vertical- and horizontal-deflection circuits of the receiver. The sync amplifier is basically a class C limiter stage. With the video signal applied, the stage is biased beyond cutoff by the grid leak bias network formed by the 470-picofarad capacitor Co and the 0.68-megohm resistor R= i in the control-grid circuit. Only the sync pulses in the composite video signal have sufficient amplitude to drive the sync amplifier into conduction. The result ant pulses developed across the out put voltage-divider network are used as the synchronizing inputs to the horizontal- and vertical - deflection circuits.
29-27 VERTICAL- AND HORIZONTAL-DEFLECTION CIRCUITS AND HIGH-VOLTAGE RECTIFIER
For Black-and-White Television Receiver
Circuit Description
These circuits develop the vertical and horizontal scanning signals and the dc operating potentials for the picture tube (RCA Type 16BGP4) used in the black-and-white television receiver and the boosted B + voltage (+250 volts) used in the audio detector-amplifier (part of circuit 29-26. The circuits operate from a dc supply of 150 volts. With the exception of the 1G3GT (or 1B3GT) high-voltage rectifier tube, the heaters of the various tubes are connected in series with those of tubes in other sections of the receiver and are supplied by the input ac power line. Heater power for the 1G3GT (or 1B3GT) is provided by a 1.25 volt winding of the high-voltage transformer T1.
The vertical- and horizontal deflection circuits are synchronized by negative signals from the sync amplifier (separator) which include horizontal sync pulses, equalizing pulses, and vertical sync pulses.
When the composite video signal is generated at the television broadcast station, the leading edge of each horizontal sync pulse, of alternate equalizing pulses, and of alternate serrations of the vertical sync pulses are correctly timed to initiate the horizontal-retrace period. It is necessary, therefore, to extract the leading-edge components from the combined sync waveform prior to application of the synchronizing input to the horizontal-deflection circuit. Similarly, the vertical sync pulses must be separated from the combined waveform before they can be used to synchronize the vertical - deflection circuit.
The combined sync waveform is differentiated at the input to the …
---------------
722 29-27 VERTICAL- AND HORIZONTAL-DEFLECTION CIRCUITS AND HIGH-VOLTAGE RECTIFIER (Cont'd) Notes: 1. Voltages shown are obtained with no signal input.
2. For dc voltage and heater supply, see circuit 29-28, page 725.
3. See additional notes on page 712.
Parts List C1=0.0039 ceramic, 500 V, N5600 Cj=0.01 uF. ceramic, 500 V C3, Co=0.047 *iF, paper, 200 V C1=0.033 uF, paper, 200 V Cs=0.027 pF, paper, 600 V Cy=0.015 uF, tubular paper, 200 V C?=0.022 nF, paper, 200 V Cs=0.0022 tiF, paper, 1000 V CM=0.0012 nF, ±5'/,,, ceramic, 500 V, N3300 Cu=180 pF, ±5r / ( , ceramic, 5000 V, N2200 C1 2=47 pF, ceramic, 2500 V.
N1500 C1a=0.0033 uF, ceramic, 500 V Cu=68 pF, paper, 500 V, N1500 C1r,=470 pF, ceramic, 500 V Cu>=0.0039 uF, mylar, 400 V C 17-0.001 uF, ceramic, 500 V C1«=0.0033 uF, ceramic, 500 V Cm=0.001 uF, ceramic. 500 V C»=0.056 uF, paper, 200 V Cm=150 uF, ceramic, 500 V Ca==390 pF, mica, 500 Cm=68 pF, ceramic, 500 V, NPO
Li=Oscillator cuil, RCA Stock No. 114486 or equiv.
Lu, L:;=RF chokes (reactors), 8.2 uH, RCA Stock No.
107385 or equiv.
P C1=Printed circuit (includes 0.001-uF and 0.0024- uF capacitors and 68000-ohm resistor), RCA Stock No. 114506 or equiv.
Ri=0.1 megohm, 0.5 watt R»=47 ohms, 0.5 watt
R:i, Ri=0.82 megohm,
0.5 watt Rr.=2.2 megohms, 0.5 watt R.;=47000 ohms, 0.5 watt
R7=Height control, potentiometer, 0.75 megohm
Rk=820 ohms, 1 watt R»=3300 ohms, 0.5 watt
R].i=Width control, potentiometer, 2000 ohms, 3 watts
Ri i=0.68 megohm, 0.5 watt
Ri:=47000 ohms, 0.5 watt
Ri:i=22 megohms, 0.5 watt
Ru=22000 ohms, 0.5 watt
Ri.-.= Vertical-hold control, potentiometer, 0.75 megohm
Ri.i^rl.8 megohms, 0.5 watt
Rit=Vertical-linearity control, potentiometer,
0.2 megohm Rit.=0.47 megohm, 0.5 watt Riii, R»r.=27000 ohms, 0.5 watt R=o, R2i=1000 ohms, 0.5 watt R=2=68000 ohms, 0.5 watt
R=::=10000 ohms, 0.5 watt
R^i=0.18 megohm, 0.5 watt
Rj,i=820 ohms, 0.5 watt Rlt=0.15 megohm, 0.5 watt
R»s=0.39 megohm, 0.5 watt
R=»=12000 ohms, 0.5 watt
R:iti=l megohm, 0.5 watt
R:u=15000 ohms, 0.5 watt
R.ii'=68000 ohms, 0.5 watt
R.c:=33000 ohms, 0.5 watt
R:n=1500 ohms, ±5%, 0.5 watt
R3.-,=4700 ohms, 0.5 watt
R.«=47000 ohms, 0.5 watt
R:t7=Horizontal-hold control, potentiometer, 70000 ohms.
SRi=Selenium rectifier, RCA Stock No. 109474 or equiv.
Tj=High-voltage and horizontal-output transformer, RCA Stock No. 114498 or equiv.
Tj=Vertical-output transformer, RCA Stock No.
114502 or equiv.
----------------------
horizontal-deflection circuit to obtain negative and positive voltage spikes which correspond to the leading and lagging edges, respectively, of the rectangular sync pulses. The amplitude of these voltage spikes is dependent upon only the peak value of the sync pulses and is not affected by the time durations of these pulses.
The differentiating circuit, therefore, does not respond to the flat portions of the vertical sync pulses, and, with the exceptions of the serrations, the vertical sync pulses do not affect the operation of the horizontal-deflection circuits. The leading edge of al ternate serrations, however, corresponds to the start of horizontal retrace periods and thus may be considered as merely another horizontal sync signal.
The differentiated sync wave form is applied to the junction of the twin silicon diodes SRi used in a phase-discriminator network. The positive portion of the differentiated waveform has no effect on the discriminator network. The negative portion is compared with a feedback signal from the horizontal oscillator to derive the synchronizing voltage.
The frequency of the horizontal oscillator and the repetition rate of the horizontal sync pulses should both be 15,750 Hz, the desired horizontal scanning rate for the picture tube. If the feedback signal from the oscillator does not occur coincident with the horizontal sync pulse, the phase discriminator develops a dc error voltage at the control grid of the input section of the 8FQ7 twin triode used in the oscillator stage.
The resultant change in oscillator bias shifts the phase of the oscillator signal until it is locked in phase with the horizontal sync pulse.
The horizontal oscillator is basically a cathode-coupled multivibrator that free-runs, in asymmetrical half cycles, at a frequency of 15,750 Hz. A parallel LC circuit connected in series with the plate of the input section resonates at 15,750 Hz to provide frequency stabilization for the horizontal oscillator. The HOLD control adjusts the basic multivibrator frequency to achieve an exact lock in with the horizontal sync pulses.
In a cathode-coupled multivibrator, one amplifier section conducts at saturation and the other section is cut off during one half-cycle of operation, and these states are automatically reversed for the next half cycle. Such circuits normally provide rectangular-wave outputs from each plate section that are 180 degrees out of phase and that switch be tween the saturation plate voltage and B+ (i.e., the cutoff plate voltage).
In the horizontal oscillator a series RC network is connected in parallel with the output tube section.
Because of this network, the plate voltage does not immediately rise to the B+ value when the output tube section is cut off. Instead, there is a small immediate rise in plate voltage that results from the voltage drop across the resistor R.is in the output RC network produced by the initial charging current to the capacitor Csi. The plate voltage then rises gradually at a rate determined by the long-time-constant circuit through which the capacitor is charged. Before the capacitor can fully charge to the B+ voltage, the combination of the horizontal sync input and the feedback signal from the plate of the output section of the oscillator drives the grid of the in put section below cutoff. The instantaneous rise in the plate voltage of the input section is coupled to the grid of the output section and causes this section to conduct. The capacitor C21 in the output RC network is then quickly discharged through the series resistor and the relatively low resistance of the output tube section. The output of the horizontal oscillator, therefore, is a trapezoidal voltage wave. The rising-slope portions of this wave (obtained when the output tube section is out off) corresponds to the horizontal-trace period on the picture tube; the discharge portion of the trapezoidal wave corresponds to the retrace period. The time-constant coupling circuits between the input and out put sections of the oscillator are designed so that the retrace period represents only about 5 to 10 percent of the over-all oscillator cycle.
The trapezoidal voltage wave is coupled to the control grid of the 22JU6 pentode horizontal - output stage and causes a sawtooth current to flow through the high-voltage (flyback) transformer Ti and through the horizontal-deflection coils of the picture tube. The gradually rising portion of the sawtooth current causes the horizontal scanning of the picture tube; the more rapid negative-slope portion of the current wave causes the retrace. During the retrace period, the picture-tube screen is blanked by a negative pulse applied to the control grid of the picture tube from the vertical-deflection circuits. The WIDTH control R10 in the screen grid of the horizontal output stage adjusts the gain of this stage to control the width of horizontal scanning.
The vertical oscillator employs a 15KY8A triode-pentode in a basic plate-coupled multivibrator configuration. This free-running 60-Hz multivibrator is synchronized by the vertical sync pulses. The vertical pulses are separated from the combined sync waveform by integration of the combined waveform across the 0.022 microfarad capacitor C7 in the control-grid circuit of the pentode output section of the multivibrator. The integrating network has negligible response for the narrow horizontal sync and equalizing pulses, but responds to the greater energy included in the much wider vertical sync pulses to develop a triangular voltage wave at the control grid of the pentode output section. The VERT LIN potentiometer Rn adjusts the charging period of the integrating capacitor to control vertical linearity. The VERT HOLD potentiometer Rw adjusts the frequency of the multivibrator to achieve an exact lock-in with the vertical sync pulses.
The voltage waveform at the control grid of the pentode output section results in a triangular wave of current through the vertical-out put transformer T2 and through the vertical-deflection coils of the picture tube. The rising portion of the tri angular current wave produces the vertical scanning, and the decreasing portion of the wave provides the retrace. Blanking pulses to cut off the picture tube during vertical and horizontal retrace periods are coupled from the secondary of T« and from the VERT LIN potentiometer (combined sync waveform before integration) to the control grid of the picture tube.
The 1G3GT (or 1B3GT) half wave rectifier circuit develops the dc operating voltages for the picture tube. The ac input power to the rectifier is supplied by the horizontal-deflection circuits. The sudden cutoff of plate current in the horizontal-output stage at the beginning of the retrace period causes a very large, positive-going voltage pulse to be generated across the high voltage transformer Ti. The rectifier converts this voltage pulse to a dc output voltage of approximately 18,000 volts, which is applied to the inner coating of the picture tube.
Removal of negative overshoots that would be developed across the high voltage transformer because of a flywheel effect is accomplished by connection of a 17BS3A rectifier (damper) tube across the horizontal deflection coils which are in parallel with the lower tapped section of the high-voltage transformer. The polarity of the damper tube is such that the positive pulse developed across the high-voltage transformer causes no current flow through it. For negative pulses, however, the damper tube provides a low-impedance path for the current, and energy stored in the horizontal-deflection coils during the preceding half-cycle is dissipated as heat at the damper-tube plate to prevent oscillation in the coils. The current through the damper tube develops a dc voltage of 450 volts across the 0.027-microfarad capacitor C» in the cathode circuit. The 0.68-megohm dropping resistor R12 reduces this voltage to obtain the boosted B+ of 250 volts required for operation of the audio detector-amplifier (part of circuit 29-25).
29-28 LOW-VOLTAGE AND HEATER SUPPLY
For Black-and-White TV Receiver
Circuit Description This circuit includes the low voltage ( + 150-volt) dc power sup ply and the series heater connections for circuits 29-24 through 29 27. As mentioned previously, the power supply and these four circuits comprise a complete black-and white television receiver, with the exception of the picture tube and the vertical- and horizontal-deflection yokes.
The power supply is a half-wave type which uses a 1N3194 silicon rectifier. The 11 7-volt ac input is connected to the power supply through an interlock, S1, which may be mounted on the back cover of the receiver. AC input power is then automatically disconnected from the receiver when the back cover is removed. ON-OFF switch S2 controls the application of ac power to the power-supply circuit and to the tube heaters. With S, and Ss both closed,
Parts List
=0.22 #F, paper, 600 V Cs=0.001, ceramic. 500 V,
>art of assembly with Li
=680 pF, ceramic, 1000 V
=250 uF, electrolytic, 200 V
Co=680 pF, ceramic, 100 V
=400 uF, electrolytic, 175 V
=0.001 uF, ceramic, 500 V
=1000 pF, feedthrough, 5000 V
F1=Fuse, chemical, 0.45 ampere, RCA Stock No. 114446 or equiv.
L1=RF choke, part of heater printed-circuit board, RCA Stock No. 114499 or equivalent (includes the two 0.001-uF capacitors C2 and C5)
L2=Filter choke (reactor), RCA Stock No. 114501 or equiv.
La=RF choke for VHF tuner filament circuit
R1=Resistor-fuse, 0.35 ohm, RCA Stock No. 114481 or equiv.
R2=330 ohms, 1 watt
TH1=Surge protection resistor (thermistor), 16 ohms (cold), RCA Stock No. 114480.
---------------------
the 117-volt power from the ac power line is applied to the series heater network and to the 1N3194 rectifier circuit. Two 0.001-microfarad (C2 and Cs) and two 680-picofarad (Co and Co) bypass capacitors and rf chokes L1 and L3 are included in the heater circuit to filter out any stray high frequency signals that may be coupled from the rf and if signal channels.
The 117-volt ac input is converted to pulsating dc by the 1N3194 silicon rectifier. A capacitor-input, pi-type LC filter network filters the rectifier output to obtain a smooth dc voltage that approaches the peak value of the input ac voltage. The 680-picofarad capacitor Cs in parallel with the 1N3194 rectifier and the thermistor TH1 in series with it provide surge-current protection for the rectifier. Initial surges of current that may result when power is first applied to the circuit (before a charge is developed across the input filter capacitor) are partially bypassed by the 680-picofarad capacitor and are limited in magnitude by the cold resistance of the thermistor.
The Circuit Description (Cont'd) thermistor has a negative tempera ture coefficient of resistance, and by the time the charge of the input capacitor Cj builds up sufficiently to limit the current through the rectifier to a safe value, the resistance of the heated thermistor is small enough so that circuit power losses across this device are negligible. The resistor-fuse element Ri in series with the 1N3194 rectifier provides protection against any continuous circuit overload. The +150-volt output from the power-supply filter network is used as the main B+ voltage for the television receiver. The 330-ohm, 1-watt dropping resistor R« at the out put of the filter network reduces this voltage to the +140 volts required as the B+ voltage in the vhf tuner.
COLOR TELEVISION RECEIVER
Circuits 29-29 through 29-35 comprise a complete portable color television receiver. The brief signal tracing analyses of these circuits assume that the reader has a basic knowledge of the purpose and operation of the various circuit sections of a color receiver. (The analyses can be more easily understood if the reader reviews the general discussions on television circuits given in the section on Electron Tube Applications starting on page 15). The receiver, which is essentially identical to the RCA Type CTC-22, features direct-line operation; the chassis of circuits 29-29 through 29-35, therefore, are connected to one side of the ac line during operation. Servicing of these circuits should not be attempted by persons not familiar with the precautions necessary when working on this type of equipment. (See notes 1 and 2 on page 712.)
Note: Circuits 29-29 through 29-35 are included in this manual primarily to illustrate applications of RCA electron tubes. Because of the exceptionally high voltages (up to 21,500 volts), high frequencies, and large bandwidths that are required and of the many special components that are used, home construction of these circuits is not recommended.
29-29 LOW-VOLTAGE POWER SUPPLY, DEGAUSSING COIL, AND HEATER CONNECTIONS
For Color Television Receiver
Circuit Description
This circuit includes the low voltage (+280-volt) dc power supply, degaussing circuitry, and heater connections for a color television receiver. The tube heaters, with the exception of the color picture tube, are connected in series across the ac power line. Heater power for the picture tube is supplied by trans former T1. With ON-OFF switch S1 closed, the 117-volt power from the ac power line is applied to the series heater string and to the primary of transformer T1. The 117-volt ac in put power is stepped down by trans former T1 to 6.3 volts at 1.0 ampere and applied to the heater of the 15LP22 color picture tube. Bypass capacitors and rf chokes are included in the series heater string to filter out any stray high-frequency signals that may be coupled from the rf and if signal channels of the receiver.
Two silicon rectifiers CR1 and CR2 are used in a voltage-doubler circuit to convert the 117-volt ac in put power to the +280-volt B+ sup ply voltage for the receiver. This doubler circuit also provides a 160 volt output from the junction of resistors R4 and R6, a +140-volt output from the junction of resistor R3 and capacitor G,, and a 95-volt output from the junction of resistor Rs and capacitor C15. The dc voltage outputs …
Parts List
C1=0.047 uF, paper, 600 V
C2=250 uF, electrolytic. 175 V
C3=50 uF, electrolytic, 250 V
C1=100 uF, electrolytic, 300 V
Cs=150 uF, electrolytic, 350 V
Co=100 uF, electrolytic, 350 V
C7 through C14=1000 pF, ceramic, 500 V C1o=2 uF, electrolytic, 175 V
CBi= Circuit breaker (includes Rs), RCA Stock No.
120784 or equiv.
CR1, CR2=Silicon rectifiers, RCA Stock No. 113998 or equiv.
Fi=Fuse, 7-ampere, 250-voIt Li, L.2=Inductor, 60-Hz line filter Li3, Li=Degaussing coils, RCA Stock No. 120793 or equiv.
Ls=Filter choke, RCA Stock No. 120792 or equiv.
Le, L7, Ls=RF choke Ri=2 ohms, wirewound, 7 watts R2=1.3 ohms, part of CBi Rs-3900 ohms, wirewound.
10 watts R4=47000 ohms, 1 watt Rs=10000 ohms, 7 watts Si=ON-OFF switch, single pole, single-throw S«=Degaussing switch, RCA Stock No. 120829 or equiv.
T1=Filament transformer primary, 117-volt ; secondary, 6.3-volt, 1-ampere
THi=Thermistor ; cold resistance, 120 ohms See Note on page 726.
-----------------
are filtered by the pi-section filter network formed by L.-,, Cs, and C.
The ac line is protected against any continuous circuit overload by a 7-ampere fuse, Fi, connected in series with one side of the line to ground.
Surge protection is provided by a thermistor TH1 connected in series with the B+ rectifiers (CR1 and CR2). The B-f circuit is protected by a special thermal reset circuit breaker CB,. The circuit breaker opens the B+ line whenever the current demand on the low voltage power supply or the current through the horizontal output stage becomes excessive.
The circuit breaker has a resistive winding (approximately 1.3 ohms) that completes the ground return for the horizontal output tube.
If the cathode current of the output tube becomes excessive, the resistive winding heats and causes the bi metal strip in the circuit breaker to expand unequally. The resultant flexing of the bi-metal strip disconnects the breaker switch contacts and thereby opens the B+ line. The same action occurs when the B+ current demand becomes excessive.
Degaussing of the color receiver is initiated by depression of the spring-loaded switch S? to the deGAUSS position. With S: in the NORMAL position, capacitors C; and C3 are combined in parallel to provide the charging capacitance for the voltage-doubler circuit. For this condition, the parallel capacitors C=
and Ca are charged to approximately 142 volts and capacitor C1 is charged to 140 volts to provide the -f-280-volt B+ voltage. When S2 is depressed to the DEGAUSS position, capacitor Cs is disconnected from the circuit, and degaussing coils La and L, are connected in series with the power supply rectifiers and capacitor Ca.
When the line voltage swings positive, C3 is charged through d, degaussing coils La and L,, and CR2;
when the line voltage is negative, C3 is charged through CR1 and the degaussing coils. This alternate cycling results in a symmetrical decaying wave train through the degaussing coils. The degaussing coils physically are looped about the receiver chassis in proximity to the color picture tube. The alternating magnetic fields developed by the decaying current wavetrain through these coils effectively demagnetizes the picture tube and adjacent chassis areas. The wavetrain decreases to zero when Ca is charged to twice the peak value of the line voltage (approximately 330 volts dc). The degaussing action is completed in less than 1 second. It is only necessary, therefore, to momentarily depress switch S2 to the DEGAUSS position. When the switch is released, it automatically returns to the NORMAL position.
29-30 VHF TUNER For Color Television Receiver
Circuit Description
This vhf tuner operates from a dc voltage of +280 volts obtained from the low-voltage power supply in the color television receiver. The tuner employs a 2EG4 nuvistor tri ode in the rf amplifier stage and uses a 4KE8 triode-pentode for the oscillator and mixer stages. The heaters of these tubes are connected in series with those of other tubes in the receiver; power for the series-heater string is obtained directly from the 117-volt ac power line. This tuner is very similar to
Note: Switches S1 through Sr. are Ranged together on the same shaft and arc shown in channel 13 position.
Parts List
C1=0.033 uF, paper, 200 V C2, C20, Cra, C24=1000 pF, feedthrough, BOO V Ca=47 pF dr5%, ceramic, 600 V, N750 C»=2 pF, feedthrough, RCA Stock No. 119595 or equiv.
Cs=Trimmer, 2 to 10 pF, RCA Stock No. 112038 or equiv.
Ca=27 pF ±5%, ceramic, 600 V, N750 C7=47 pF, feedthrough, 600 V Cs, Co, C1o, Cu=27 pF
±6%. ceramic, 600 V, N470 C12=2.7 pF, headed lead, 600 V C1s=33 pF, ceramic, 500 V, N750 Cn=39 pF. feedthrough, 500 V C1s=4.7 pF ±6%. headed lead, 600 V C1e=680 pF, ceramic, 500 V C17=62 pF ±5%, ceramic, 1000 V, N1500 C18=27 pF, ceramic, 500 V C1b=2 pF, ceramic, 600 V, NPO C2i=5.6 pF ±6%, ceramic, 600 V, N150 C22=27 pF, ceramic, 500 V, NPO C26=0.047 uF, ceramic, 500 V Li=RF amplifier grid coil, part of S3 assembly L2=UHF trap La=RF amplifier grid-circuit coil, part of Sb assembly ht, Ls, Lo=Filter coils for high-pass filter network, part of Ti assembly L.7=RF amplifier plate coil.
part of S3 assembly Ls through Lis-RF amplifier plate-circuit tuning coils, part of S3 assembly Li» through L28=Antenna tuning coils, part of Ss assembly L29, L3o=High-band coupling adjust coils L,3i=Mixer grid coil, part of Ss assembly L.32 through L,42=Mixer tuning coils, part of Ss assembly L43, L*4=Low-band coupling adjust L,46=RF amplifier grid-circuit coil, part of Ss assembly L,4o=IF input coil for signals from uhf tuner, RCA Stock No. 120782 or equiv.
L*7=RF coil, part of input circuit for signals from uhf tuner Li8=Mixer plate coil, RCA Stock No. 112909 or equiv.
L«=RF filter coil
Lso=Channel 13 range centering coil Lsi through Lo«=Local oscillator tuning coils, part of S1 assembly Ji, j2=Single-contact female connector, RCA Stock No.
104039 or equiv.
Ri=47000 ohms, 0.5 watt R2=16000 ohms, 3 watts R3=4700 ohms, 1 watt Rt=82000 ohms, 0.5 watt Rs=1500 ohms. 0.6 watt Ro=10000 ohms, 0.5 watt R7=2200 ohms, 0.5 watt Rs. Rio=10 ohms, 0.5 watt R», Ris=1000 ohms, 0.5 watt Ru=27000 ohms, 0.5 watt Ri2=68000 ohms, 1 watt Ri4=5600 ohms, 0.5 watt Ri5=6800 ohms, 0.6 watt Rio=680 ohms, 1 watt Si=Local-oscillator section of channel-selector switch stator assembly, RCA Stock No. 114837 or equiv., includes local-oscillator tuning coils L51 through L02 S2=Mixer section of channel selector switch ; stator assembly, RCA Stock No. 120084 or equiv., includes mixer tuning coils L31 through Lja S3=RF amplifier section of channel-selector switch ; stator assembly, RCA Stock No. 120086 or equiv., includes rf amplifier plate tuning coils L7 through Lis S4=UHF function switch assembly ; part of channel selector switch ; stator assembly, RCA Stock No. 114807 or equiv.
Ss-Antenna section of channel-selector switch stator assembly, RCA Stock No. 120087 or equiv., includes antenna tuning coils Li, L45, and Lib through L28 Ti=Antenna matching trans former (includes coils Li, L5, and Ls in high-pass filter network), RCA Stock No. 113968 See Note on page 726.
-----------
the tuner for a black-and-white television receiver (shown in circuit 29 24), and it operates equally well for either color or black-and-white trans missions.
The antenna used with the tuner is a balanced 300-ohm dipole type which is matched to the unbalanced tuner input circuit by the antenna matching transformer TV The ganged 5-section, 13-position channel selector, S1 through S5, establishes the operating frequency of the tuner for each of the vhf channels 2 through 13 or adapts the vhf tuner for operation with a uhf tuner.
When used with a uhf tuner, the vhf tuner is operated as a two stage broadband rf amplifier and becomes essentially a pre-if amplifier for the color television receiver.
With the channel selector set to any of the channel positions 2 through 13, telecast signals, either color or black-and-white, from the selected channel are coupled from the antenna circuit through sections S4 and S6 of the channel selector to the control grid of the 2EG4 rf amplifier.
For channel positions 2 through 13, the input lead (IP INPUT) from the uhf tuner is not connected to the vhf tuner.
The vhf input signals are amplified by the rf amplifier. The S5 and Sa sections of the channel selector connect the appropriate combinations of inductors into the grid and plate circuits of the rf amplifier to tune this stage to the desired frequency channel. An age bias voltage, derived from the keyed age amplifier in another section of the color receiver (circuit 29-32), is applied to the control grid of the 2EG4 to control the gain of the rf amplifier automatically.
The output of the rf amplifier is coupled through sections Sa and S» of the channel selector to the control grid of the 4KE8 pentode section used in the mixer stage. Section Sj of the ganged channel selector selects the proper combination of inductors to tune the mixer input circuit to the same operating frequency as that of the rf amplifier.
A signal from the plate of the 4KE8 triode section used in the local oscillator stage is also applied to the mixer. Section S1 of the channel selector selects the required inductance so that the oscillator operates at a frequency 45.75 MHz above the video carrier frequency of the vhf channel selected by the tuner.
The signals from the rf amplifier and local oscillator are heterodyned in the mixer stage to produce the 45.75-MHz amplitude-modulated and 41.25-MHz frequency-modulated difference frequencies used as picture and sound intermediate frequencies, respectively. The composite color signal received at the antenna also includes a 3.58-MHz color subcarrier sideband. This subcarrier is also heterodyned with the local-oscillator frequency to produce a color-sub carrier intermediate frequency of 42.17 MHz. The picture, color-sub carrier, and sound if signals are coupled from the plate of the mixer through J2 to the if stages of the receiver.
When the multiple-section channel selector is rotated to the UHF position, Ss disconnects the vhf antenna circuit from the rf amplifier, and section S4 completes a connection to the 280-volt B+ line through several voltage-dropping resistors to provide a dc voltage output of 18 volts for use as the B+ voltage for a uhf tuner. The video, sound and color-subcarrier if signals from a uhf tuner can then be applied through the IF INPUT jack Ja and contacts of S4 and S5 to the control grid of the 2EG4 rf amplifier.
With the channel selector in the UHF position, switch section S1 opens the B+ line to the local oscillator to disable this stage. In addition, sections Si, S3, and S8 select the proper combination of components so that the rf amplifier and mixer stages operate as broadband 44-MHz amplifiers to provide two stages of amplification of the picture and sound if signals ahead of the receiver main if strip.
29-31 VIDEO-AND SOUND-CHANNEL CIRCUITS
For Color Television Receiver
Parts List
C1=5 pF, part of Ti C:=1000 j)F ±5%, ceramic, 500 V
Cs, Cs, Cd, C14=0.01 /xT, ceramic, 500 V
Cj=10 pF ±5%, ceramic, 600 V, NPO
Co=1.5 pF, ceramic, 500 V.
NPO Ct=6 pF, part of T2
Cs=47 pF, ceramic, 500 V, N760
C1o=150 pF, part of Ta
Cn=39 pF, ceramic, 500 V, N750
C1?=560 pF, ceramic, 500 V
C1a=10 pF, part of Tt C1.-,=4 pF, ceramic, 500 V Cm=10 pF, ceramic, 500 V, NPO
Cn=6800 pF, ceramic, 500 V C1s=47 pF, ceramic, 500 V, N750 Cm=0.047 pF, ceramic, 500 V Czo=0.0033 uF. paper, 1600 V C:i=Trimmer, 3 to 15 pF, RCA Stock No. 116502 or equiv.
C=L>=150 pF ±5%, mica, 500 V C=3, C20, C=s, C.f,=1000 pF, ceramic, 500 V
C.m=330 pF, mica, 500 V C».-,=24 pF, ceramic, 500 V, NPO
These circuits form the video and sound channels for a color television receiver. The circuits operate from a dc supply voltage of 280 volts, obtained from the receiver low-voltage power supply. The tube heaters are included in the series heater string for the over-all receiver. Operating power for the series-heater string is obtained directly from the 117-volt ac power line.
The picture if-amplifier circuit consists of two high-gain stages that use high-transconductance frame grid tubes and double-tuned inter stage coupling transformers. The composite if input from the vhf tuner which consists of amplitude modulated 45.75-MHz picture signals 42.17-MHz color-subcarrier components, and frequency-modulated 41.25-MHz sound signals, are coupled by capacitor Ca and transformer T« to the control grid of the 3KT6 pentode used in the first picture if
----------
Cs7=4700 pF, ceramic, 500 V C»=430 pF ±6%, mica, 500 V Cao=150 pF, mica, 500 V
Cai=0.047 uF, Mylar, 100 V C32=0.047 uF, ceramic, 100 V C33=0.1 uF, Mylar, 100 V Cm=560 pF, ceramic, 500 V Caj=680 pF, ceramic, 500 V Ca7=220 pF, ceramic, 600 V
Css=50 uF. electrolytic, 50 V CR1, CR2, CR3=1N60 diode CR4=Vertical-blanking diode, RCA Stock No. 115867 or equiv.
DLi=Delay line, RCA Stock No. 120786 or equiv.
Li=RF choke, 3.9 »H, RCA Stock No. 116507 or equiv.
L.2. Lio=RF choke, 1.8 uH, RCA Stock No. 109248 or equiv.
La=RF choke, 12 uH, RCA Stock No. 120831
L«=Inductor for 47.25-MHz trap, RCA Stock No.
121447 or equiv.
Ls=Video-detector filter coil, 6.6 uH, RCA Stock No. 109171 or equiv.
La, Ls=Part of 4.5-MHz trap, RCA Stock No.
121446 or equiv.
L7=Video-detector filter coil, 36 uH. RCA Stock No.
16056 or equiv.
Lb=RF choke, 100 uH. RCA Stock No. 117380 or equiv.
Ln=Filter coil. 27 uH, RCA Stock No. 116511 or equiv.
Li2=Filter network (includes resistor R32) ; RCA Stock No. 116499 or equiv.
Lia=Second-video plate coil.
330 uH, RCA Stock No. 118710 or equiv.
Li4=First-video plate coil, 1.8 uH. RCA Stock No. 78466 or equiv.
Ri, Re, R35, R«=270 ohms, 0.5 watt
R2, R2s=10000 ohms, 0.5 watt R:!=8200 ohms, 0.5 watt
R*=0.15 megohm, may be part of T» Rr,=3300 ohms, 0.5 watt
R7=0.68 megohm, 0.5 watt Rs=0.47 megohm, 0.5 watt Rb=t68000 ohms, may be part of T» Rio=Potentiometer, volume control, 1 megohm, 0.5 watt Rn=Potentiometer, sound rejection adjustment, 7500 ohms, 0.5 watt Ri»=0.33 megohm, 0.5 watt
R13, R.io=0.1 megohm, 0.5 watt
Ri4=3900 ohms, ±5%, 0.5 watt
Ri5=56 ohms, ±5%, 0.6 watt
Rm=1000 ohms, 0.5 watt
Ru=22000 ohms, 4 watts
Ri»=6800 ohms, ±5%, 0.5 watt
Rm=150 ohms, ±5%, 0.5 watt
R»=470 ohms, 0.5 watt
R2i=1200 ohms, 0.5 watt
R22=4700 ohms, 0.5 watt
R23=0.18 megohm, 0.5 watt
R2<=5.6 megohms, 0.5 watt
R2b=22 megohms, 0.5 watt
R27=2.7 megohms, 0.5 watt
R28=Potentiometer, brightness control, 0.25 megohm, RCA Stock No. 120775 or equiv.
R2e=680 ohms ±5%, 0.5 watt
R3i=0.22 megohm, 0.5 watt
Rs2=2200 ohms, part of assembly with Li2
R33=0.39 megohm, 0.5 watt
Rn=0.12 megohm, 0.5 watt
R3o=100 ohms, 0.5 watt
Ra7=5600 ohms. 0.5 watt
Ros=560 ohms, 0.5 watt
Rso=22000 ohms, 3 watts
R4i>=6800 ohms, 4 watts
R4i=10000 ohms, 3 watts
R4==33000 ohms, 4 watts
T1=Sound-takeoff trans former (includes C1), RCA Stock No. 120824 or equiv.
T2=4.5-MHz sound if transformer (includes Ct and may include R4), RCA Stock No. 120828 or equiv.
T;i=Pix if output transformer and 41.25-MHz trap, RCA Stock No. 120827 or equiv.
T4=Sound-demodulator quadrature network (includes C13 and may include Ro), RCA Stock No. 120825 or equiv.
T.-,=Audio output transformer, matches 5000-ohm tube-plate impedance to 3.2-ohm speaker voice coil, RCA Stock No. 120822 or equiv.
Tn=IF input transformer and 41 25-MHz trap, RCA Stock No. 116560 or equiv.
T7=Pix if transformer, RCA Stock No. 120826 or equiv.
See Note on page 726.
----------------
... amplifier. The 3KT6 tube has good remote-cutoff characteristics, and the automatic-gain-control (age) bias voltage from the receiver age amplifier (shown in circuit 29-32) is also applied to the control-grid circuit of this tube. The output of the first picture if amplifier is coupled by transformer T7 to the control grid of the 3JC6A pentode used in the second picture if amplifier. Capacitor Co couples the output of the second picture if amplifier to the sound detector, and transformer T3 couples the output to the video (pix) detector. Transformers T„, T7, and T3 are stagger-tuned to obtain the wide band pass required for the if amplifiers to pass both the 45.75-MHz video AM signals and the 41.25-MHz sound FM signals, as well as the intermediate 42.17 color subcarrier.
The sound detector (CR1 and associated components) is essentially a second mixer circuit. The 45.75 MHz picture if signal and the 41.25 sound if signal are heterodyned to produce a second sound if carrier of 4.5 MHz. This 4.5-MHz sound if carrier is still frequency-modulated by the audio components contained in the original rf signal input at the receiver antenna. The sound-takeoff transformer Ti forms a selective load impedance for the 4.5-MHz if signal derived in the sound detector circuit.
The 4.5 MHz signal developed across sound-takeoff transformer T, is applied to the control grid of the 3JC6A sound if amplifier. The amplified 4.5 MHz FM if signal from this stage is then coupled by the double tuned transformer T» to the control grid of the 5HZ6 sound demodulator.
This stage demodulates the 4.5 MHz sound if signal and amplifies the resultant audio signal voltage.
The +490 volts used as the plate supply for the 5HZ6 demodulator tube is derived from the 700-volt B Boost supply in the horizontal output stage (shown in circuit 29 33) of the receiver.
The tuned secondary circuit of transformer T3 selects the 45.75 MHz amplitude-modulated picture and 42.17-MHz color sideband signals from the composite if signal and applies this picture signal to the video detector (CR= and associated components). The detected video signal developed across the detector circuit filter network (L5, Lo, In, L8, and Cm) is then coupled through C3 i and R«3 to the control grid of the 5GH8A triode section used in the first video amplifier (the pentode section of the 5GH8A tube is used in the sync-agc-and-chroma driver, shown in circuit 29-32). The first video amplifier supplies the input signals to the sync-agc-and-chroma driver and to the second video amplifier.
The second video stage performs many functions. The input circuit of the 11HM7 pentode used in this stage is the insertion point for horizontal blanking pulses (for eventual application to the cathodes of the color picture tube). The horizontal blanking diode CR3 is placed in the conducting mode by a small positive voltage applied to its anode through the dropping resistor RM from the 280-volt B+ source. During active video scanning time, diode CR3 is forward-biased (conducting), and the video signal is coupled by capacitor Cm, to the control grid of the video amplifier. During horizontal blanking time, a negative pulse from the horizontal-output transformer (Ti in circuit 29-33) is applied through Cm and R3 i to the diode.
This negative pulse is sufficient to cut off the diode during horizontal retrace time. The pulse is applied to the control grid of the second video amplifier and drives the grid more negative (than would the nor mal horizontal sync pulse). The negative signal at the grid is inverted at the plate; the added positive level coupled to the cathodes of the color picture tube is sufficient to provide blanking of horizontal retrace lines.
The brightness control for the color receiver is also located in the control-grid circuit of the second video amplifier. Negative dc grid bias for the 11HM7 second video tube is derived from the ac voltage obtained from the heater, pin 6, of the second video tube. The 11HM7 heater is in the approximate center of the series heater string (refer to circuit 29-29); at this point, approximately 60 volts of ac voltage is available. The negative dc voltage (about -75 volts) is developed across C* by the IN3194 rectifier circuit. Adjustment of the brightness control, Rai alters the grid bias by "tapping" the positive voltage applied to the top of the control. This unique circuit arrangement provides automatic brightness compensation with changes in power-line voltage. If line voltage increases, the negative voltage across C32 increases; the increased bias that is then applied to the 11HM7 decreases the conduction of this tube. The opposite action occurs with a decrease in line voltage.
The cathode of the second video amplifier is returned to the contrast control Rh. Brightness stability is obtained by use of a fixed 150-ohm, 5-percent resistor, R43, for dc cathode bias. Adjustment of the contrast control does not change the dc characteristics of the cathode; only the ac signal gain of the stage is altered when the control is adjusted.
Vertical-retrace blanking is accomplished in the plate circuit of the second video amplifier. During active scan periods, the vertical-blanking diode CR4 is forward-biased (conducts); during vertical retrace periods, however, a positive (blanking) pulse from the vertical-output transformer (T» in circuit 29-33) is applied through R as to the cathode of the diode. This 60-volt positive pulse is large enough to bias the diode into cutoff. During the blanking interval, the positive voltage pulse is added to the plate voltage of the 11HM7 second-video tube and applied to the cathode circuits of the color picture tube. As a result of the increased positive potential at the cathode, the picture tube is cut off during vertical retrace periods.
29-32 SYNC, AGC, AND VERTICAL-DEFLECTION CIRCUITS
For Color Television Receiver
Parts List
C1=0.18 uF, Mylar, 200 V
C2=24 pF, ceramic, BOO V, NPO
Ca, Cw=0.01 pF, ceramic, 500 V Cj=1000 pF, ceramic, 500 V Cs=3300 pF, ceramic, 500 V C»=470 pF, ceramic, 500 V C7=0.1 nF, paper, 600 V C»=0.0056 uF, Mylar, 400 V Co=0.01 ilF, Mylar. 600 V do, C1s=680 pF, ceramic, 500 V Cu=0.047 uF, Mylar, 100 V Cu=1500 pF, ceramic, 500 V C1s=50 uF. electrolytic, 75 V Cn=0.0082 uF, paper, 1000 V C1g=0.033 uF, Mylar. 600 V C1s=0.001 jiF, ceramic, 3000 V C1o=25 uF, electrolytic, 25 V Li=RF choke, 120 liB., part of assembly with R», RCA Stock No. 120795 or equiv.
Ri, Rie=0.15 megohm.
0.5 watt R2=Potentiometer, age adjustment. 50000 ohms,
0.5 watt, RCA Stock No.
120804 or equiv.
Rj=27000 ohms, 0.5 watt
R1=3300 ohms, 0.5 watt
Rs, Rw. Rm=10000 ohms,
0.5 watt Ra=6800 ohms, 0.5 watt
Rt=27000 ohms, 1 watt
Rs=1500 ohms, 0.5 watt
Rg=68000 ohms, 0.5 watt, part of assembly with L1
Rio-0.56 ohms, 0.5 watt
Rn=1800 ohms, 0.5 watt
R12, R27, Rm^0.12 megohm, 0.5 watt
Ris=10 megohms, 0.5 watt
Ri4=22000 ohms, 0.5 watt Ri5=10000 ohms, 3 watts Ri«-22 megohms, 0.5 watt Ri9=3.3 megohms, 0.5 watt R20-1.5 megohms, 0.5 watt R2i=Potentiometer, vertical linearity control, 3.4 meg ohms, 0.5 watt, RCA Stock No. 120807 or equiv.
R22=56000 ohms. 0.5 watt Rzi=47000 ohms, 0.5 watt R24=4.7 megohms, 0.5 watt Rik=1000 ohms, 0.5 watt Rm=1.6 megohms, 0.5 watt Rs9=0.47 megohm, 0.5 watt Roo:=33000 ohms ±5%, 0.5 watt R.t2==0.22 megohm, 0.5 watt R33=3300 ohms, 1 watt R3i=1500 ohms, wirewound, 3 watts Rso=Potentiometer, vertical height control, 1 megohm,
0.5 watt, RCA Stock No. 120805 or equiv.
Rto :0. 1 megohm, 1 watt
Rarr=Potentiometer, vertical hold control, 0.75 meg ohm, 0.5 watt VDRi=Voltage-dependent resistor (varistor) ; 870 volts at 1 mA ; RCA Stock No. 112876 or equiv.
See Note on page 726.
Circuit Description
This circuit shows the sync-agc and-chroma driver, age amplifier, sync separator, and vertical deflection circuit for a color television receiver. The sync-agc-and-chroma driver, the sync separator, and the vertical output tube operate from a plate supply (B+) voltage of 280 volts obtained from the receiver low voltage power supply. The plate supply voltage for the age amplifier is a positive keying pulse from the horizontal-output transformer, and the plate voltage for the vertical oscillator is obtained from the 700 volt B Boost supply in the horizontal output circuit. The tube heaters are connected into the series-heater string for the over-all color receiver; operating power for the heater string is obtained directly from the ac power line.
The drive signal for the sync and age circuits is obtained from the cathode of the first video amplifier (shown in circuit 29-31). This signal is coupled by capacitor Cs and the parallel LR network La and R» to the control grid of the 5GH8A pentode section used in the sync-agc and-chroma driver. (The triode section of the 5GH8A tube is used in the first video amplifier). The screen grid and control-grid bias voltages for the driver pentode are also obtained from the first video amplifier.
The output of the driver stage is applied to the control grids of the age amplifier and the sync separator and to the chroma circuits (shown in circuit 29-34).
The age amplifier uses the pentode section .of a 5GH8A triode pentode; the triode section of this tube is used in the sync separator.
The operation of the age amplifier is gated by a positive keying pulse from the horizontal-output transformer (shown in circuit 29-33). This pulse, which is synchronized with the video signal, overcomes the bias provided by the 95 volts (obtained from the receiver low-voltage power supply, circuit 29-29) applied to the cathode circuit of the age amplifier. Portions of the video signal that occur coincident with the keying pulse (i.e. during the horizontal blanking interval) are amplified by the age stage. Resistor Ri and capacitor C1, together with other filtering elements in the control-grid circuit of the first picture if amplifier, filter out the pulsating components in the video signal to obtain a negative dc voltage proportional the video signal and thus to the rf input at the receiver antenna. Similarly, an age bias voltage for the vhf tuner is developed across the filter capacitor C Synchronizing pulses are included in the composite rf signals transmitted by a television broadcast station to provide timing information required for synchronization of the transmitter and receiver scanning systems. The sync separator separates and amplifies the synchronizing pulses contained in the composite video signal it receives from the sync-agc-and-chroma driver.
The 5GH8A triode section used in this stage is operated basically as a class C limiter. When the video signal is applied, the stage is biased beyond cutoff by the negative voltage developed by the grid-leak bias network formed by C and R«. Only the sync pulses in the composite video signal have sufficient amplitude to drive the sync amplifier into conduction. The resultant negative pulses developed in the plate circuit of the 5GH8A triode section are applied as the synchronizing inputs to the vertical and horizontal deflection circuits.
The vertical-deflection circuit employs one section of a 10GF7A dual triode in a vertical oscillator stage and a vertical output stage.
These two stages form a basic plate coupled 60-Hz free-running multi vibrator that is synchronized by negative vertical sync pulses from the sync separator stage. The negative-pulse output from the sync separator, however, includes horizontal sync pulses and equalizing pulses in addition to the vertical sync pulses.
The vertical sync pulses must be separated from the composite sync separator output prior to the application of the synchronizing input to the vertical-deflection circuits. This separation is accomplished by integration of the composite sync separator output across capacitor Cn. The integrating network (Rw and C12) has negligible response for the narrow horizontal-sync and equalizing pulses, but responds to the greater energy contained in the much wider vertical-sync pulses to develop a triangular voltage wave form, coupled by C«, C», and RM to the control grid of the vertical-out put triode section, that synchronizes the operation of the multivibrator.
The combination of the triangular wave input to the grid of the output section and the square-wave multi-vibrator signal results in a trapezoidal voltage waveform at the plate of the output section. This trapezoidal voltage wave produces a tri angular wave of current through the vertical-output transformer (T» in circuit 29-33) and through the vertical deflection coils of the picture tube (shown in circuit 29-35). The rising portion of the triangular current waveform produces the vertical scanning, and the decreasing portion of the waveform provides the retrace.
29-33 HORIZONTAL-DEFLECTION CIRCUIT AND HIGH VOLTAGE POWER SUPPLY
For Color Television Receiver
Circuit Description
These circuits develop the horizontal scanning signals and the dc operating voltage (21,500 volts) for the color picture tube (RCA Type 15LP22) and the receiver B Boost voltage (700 volts). The circuits operate from the receiver low-voltage (280-volt) supply. The heaters of the 5GH8A, 24JE6A, and 17KV6A tubes used in these circuits are included in the series-heater string for the over-all receiver; operating power for these heaters is obtained directly from the 117-volt ac power line.
Heater power for the 3A3A high voltage rectifier tube is obtained from a 3-volt secondary winding on the high-voltage transformer.
A blocking oscillator in which the transformer coil is located in the cathode circuit is used to obtain a large-amplitude horizontal-drive
--------- Parts List
Cj=82 pF ±1 pF, ceramic, 500 V, NPO
C:=1200 pF, ceramic, 500 V Ca=0.0018 nF, paper, 1000 V C1=150 pF, ceramic, 500 V, NPO C3=0.16 uF, Mylar, 75 V C»=0.01 pF, Mylar, 600 V C7=0.01 uF, Mylar, 75 V Cs, C1s=1200 pF, ceramic, 500 V Co, Cu=0.1 uF, Mylar, 400 V C1n=15 pF, ceramic, 5000 V, N750 C1i, Cm=1000 pF, ceramic, 500 V C12, Cn=0.01 uF, Mylar, 400 V C1e=270 pF ±5%, mica, 600 V C1t=100 pF, ceramic, 5000 V, N1500 Cw=22 pF, ceramic, 1000 V, N750 C2o=0.1, Mylar, 200 V C2i=0.033 uF, Mylar, 600 V C22=0.01 ii¥, Mylar, 600 V Cw=40 uF, electrolytic, 350 V Clm=0.047 /mF, Mylar, 600 V C1t,=150 pF, ceramic, 2000 V, N1500 C2o=270 pF, ceramic, 2500 V, N1500 C1t=150 pF, ceramic, 2000 V, N1500 CRi=AFC diodes, RCA Stock No. 109474 or equiv.
CR«=Damper diode, RCA Stock No. 120818 or equiv.
Ji=Octal socket, convergence-circuit input jack.
RCA Stock No. 77645 or equiv. (mates with Pi on circuit 26-36) J2=0ctal socket, deflection yoke input jack, RCA Stock No. 102787 or equiv.
(mates with P2 on circuit 26-36) lii, I>L'=Horizontal-oscillator dual-coil assembly, RCA Stock No. 109947 or equiv.
La, L4=RF choke, 4.7 /iH, RCA Stock No. 120839 or equiv.
Ls=:Variable inductor, horizontal efficiency adjustment, RCA Stock No.
120794 or equiv.
Ri, R»2=0.22 megohm,
0.5 watt R2, Rm=0.39 megohm, 0.5 watt
fti=0.27 megohm, 0.5 watt Rt=100 ohms, 0.6 watt Rs=15000 ohms, 0.5 watt Ro=1200 ohms, 0.5 watt R7=47 ohms, 0.5 watt lis, R26=0.12 megohm, 0.5 watt Re=0.15 megohm, 0.5 watt Rio=82000 ohms, 0.5 watt Rn=8.2 megohms, 0.5 watt Ri»=680 ohms, 2 watts Ru=82000 ohms ±2%, 0.5 watt Ru=82000 ohms ±5%, 4 watts Ris=100 ohms, 0.5 watt Rie=68000 ohms, 1 watt Rw=33000 ohms, 0.5 watt Ria=1000 ohms. 2 watts Ri9= 10000 ohms, 0.5 watt R=i=27000 ohms, 0.5 watt R^t=10 megohms, 0.5 watt R24=Potentiometer, high voltage adjustment, 0.5 megohm, 0.5 watt R25=33000 ohms, 0.5 watt R27=0.56 megohm, 0.5 watt B.2a-0.27 megohm, 1 watt Ra>=120 ohms, 0.6 watt Rao=:2.2 megohms, 0.5 watt R3i=Potentiometer, horizontal-hold control, 50000 ohms, 0.5 watt SGi=Spark-gap capacitor, 0.5 pF. 1000 V, RCA Stock No. 120819 or equiv.
Ti=Horizontal-output (fly back) transformer, RCA Stock No. 120820 or equiv.
T»=Vertical-output trans former, RCA Stock No. 120821 or equiv.
See Note on page 726.
-------------
... waveform. A control stage establishes the bias for the oscillator and, in this way, controls the firing of the oscillator stage. The 5GH8A triode-pentode is used in these stages. The triode section is used as the oscillator tube; the pentode section is used as a high-gain, low-drift control tube.
When the composite video signal is generated at the television broad cast station, the leading edge of each horizontal sync pulse, of alternate equalizing pulses, and of alternate serrations of the vertical sync pulses are correctly timed to initiate the horizontal retrace period. These leading-edge components are extracted from the composite output from the sync separator (shown in circuit 29-31) and are used to synchronize the operation of the horizontal oscillator.
The sync waveform is differentiated by the RC network ( C1 and R») at the input to the horizontal deflection circuit to obtain negative and positive voltage spikes that correspond to the leading and lagging edges, respectively, of the rectangular sync pulses. The amplitude of these voltage spikes is dependent upon only the peak value of the sync pulses and is not affected by the time durations of these pulses.
The differentiating circuit, therefore, does not respond to the flat portions of the vertical sync pulses; as a result, with the exception of the serrations, the vertical sync pulses do not affect the operation of the horizontal-deflection circuits. The leading edge of alternate serrations, how ever, correspond to the start of horizontal-retrace periods and thus may be considered as merely another horizontal sync signal.
The differentiated sync wave form is applied to the junction of the twin silicon diode CR1 used in a phase-discriminator type of afc net work. The positive voltage spikes in the differentiated waveform have no effect on the discriminator network.
The negative-voltage spikes are com pared with pulses fed back from the horizontal oscillator to derive the synchronizing voltage. The frequency of the horizontal oscillator and the repetition rate of the horizontal sync pulses should both be 15,750 Hz, the desired horizontal scanning rate for the picture tube. If the pulses from the oscillator are not coincident with the horizontal sync pulses, the phase discriminator develops an error voltage at the control grid of the control tube. The control tube then varies the bias and, thus, the firing point of the oscillator until it is locked in phase with the horizontal sync pulses.
The parallel LC network (L2 and C1«) in the cathode circuit of the oscillator resonates at 15,750 Hz to provide frequency stabilization for the oscillator. The HOLD control Rsi adjusts the frequency of the oscillator to achieve an exact lock-in with the horizontal sync pulses. The out put of the blocking oscillator is coupled through Ch and Ri to the control grid of the 24JE6A power pentode used in the horizontal-out put stage. This tube drives the high voltage flyback transformer Ti that develops the scanning voltage for the horizontal deflection coils (shown in circuit 29-35.
The sudden cutoff of plate current in the horizontal output stage at the end of the trace period causes a very large, positive-going voltage pulse to be generated across the high-voltage transformer Tj. The 3A3A half-wave rectifier circuit converts this pulse to a positive dc of 21,500 volts which is applied to the second anode of the color picture tube.
Regulation of the high voltage is achieved by use of a 17KV6A pulse-regulator stage connected in shunt with a section of the primary of the high-voltage flyback trans former. The regulator stage acts as a variable load on the flyback pulse source and, in this way, maintains an essentially constant pulse amplitude in the primary winding of the high-voltage transformer with changing loads on the high-voltage supply. This action assures that a constant-amplitude, stepped-up pulse is applied to the 3A3A rectifier. The rectifier output delivered to the picture tube, therefore, is maintained at a constant value of 21,500 volts.
Removal of negative overshoots that would be developed across the high-voltage transformer because of a flywheel effect is accomplished by the damper diode CR2. This diode is shaped like a fuse and snaps into clips that can be mounted on the same circuit board with the horizontal deflection circuits and is readily replaced during servicing.
The polarity of the damper diode is such that the positive pulse developed across the high-voltage transformer causes no current flow through it. For negative pulses, however, the damper diode provides a low impedance path for the current, and energy stored in the horizontal output transformer (and the horizontal deflection coils) is dissipated in the damper circuit. The rectified current through the damper diode develops the boosted B-f- voltage of +700 volts across capacitor Cm in the damper anode circuit.
The two auxiliary windings on the high-voltage transformer supply supplementary pulse voltages. The upper winding supplies gating pulses to the burst-gate and the color-killer amplifiers (shown in circuit 29-34).
The convergence pulse is developed across the lower auxiliary winding.
Keying pulses for the age amplifier and the horizontal blanking diode are derived from the capacitor net work (junction of C1b and C27) in the primary circuit of the high-voltage transformer.
Transformer Ts shown in the circuit diagram is the vertical output transformer. The drive signal from the vertical output stage (shown in circuit 29-32) is developed across the primary of this transformer and coupled by the secondary winding through jack J2 to the vertical deflection coils (shown in circuit 29-35).
An auxiliary winding on transformer T2 develops the keying pulse for the vertical blanking diode. The horizontal scanning signal from the high voltage (horizontal-output) trans former are also coupled through jack J1 to the horizontal deflection coils. The horizontal and vertical signals to the convergence board are routed through jack Js. (Jacks Ji and J» mate with plugs P2 and P1, respectively, on circuit 29-35.)
29-34 CHROMA CIRCUITS
For Color Television Receiver See Note on pave 726.
Parts List
C1=27 pF, ceramic, 500 V, NPO
C2=68 pF, ceramic, 500 V, N750
Ca, Cs. Ce, Cs, Co, Cm, Ck.
Cm through C:n=0.01 pF, ceramic, 500 V
C4=390 pF, ceramic, 500 V
C7=0.047 uF, Mylar.
100 V C1o, C1s=1000 pF, ceramic, 600 V Cn=Trimmer, 2 to 10 pF, RCA Stock No. 116501 or equiv, C1i'=220 pF, ceramic, 500 V C13=10 pF, ceramic, 500 V, N150 Cm, C1«=0.82 pF ±5%. headed lead. 500 V C1s=820 pF. ceramic. 500 V Cj7=390 pF ±S%. Mylar, 600 V C1», Csa, C27=33 pF, ceramic, 500 V. N150 C2i=10 pF ±5%, ceramic.
600 V, NPO C=4=0.027 pF, Mylar, 100 V C»5=430 pF ±5%. mica, 500 V C2s=150 pF, ceramic, 500 V C»=1.2 pF, ceramic, 500 V CRi, CRi, CRs, CRe=Silicon diode, RCA Stock No. 119596 or equiv.
CR2=Diode, pulse clipper, RCA Stock No. 113998 CR3=Diode, type 1N60 Li=Variable inductor, chroma-takeoff coil, RCA Stock No. 120797 or equiv.
L^=Variable inductor, oscillator strength adjustment, RCA Stock No.
120798 or equiv.
L.j=Phase-shift coil, 3.9 uH, part of quadrature assembly (RCA Stock No.
120830 or equiv.) with Ri-j Li=RF coil. 3.9 uH, RCA Stock No. 116510 or equiv.
Lb, Lo=RF choke, 620 uH, RCA Stock No. 109257 or equiv.
Ri=3.9 megohms, 0.5 watt Rl'=0.15 megohm, 0.5 watt Ra, R4. R7=47000 ohms, 0.5 watt Rs=82000 ohms, 0.5 watt Ro. Rio=10 megohms, 0.5 watt Rs=Potentiometer, color killer adjustment, 1 meg ohm, 0.5 watt, RCA
Stock No. 120805 or equiv.
R»=82 ohms, 0.5 watt Rn=2.7 megohms, 0.5 watt
Ril'=2.2 megohms, 0.5 watt Ri.;=3900 ohms, 0.5 watt
Rn, Rio=390 ohms, 0.5 watt Rio=82000 ohms, 0.5 watt
Riv=47000 ohms, 1 watt Ri».=560 ohms, 0.5 watt
Ri»=1500 ohms, 0.5 watt
Riii=Potentiometer, tint control, 10000 ohms,
0.5 watt, RCA Stock No. 120774 or equiv.
Ra=6800 ohms, 1 watt Rr.=120 ohms ±5%, 1 watt, part of quadrature assembly with La Rik. R:»=470 ohms, 0.5 watt R»i=1500 ohms, 0.5 watt Ris- Potentiometer, color control, 500 ohms, 0.5 watt, RCA Stock No. 120776 or equiv.
R?7=0.1 megohm, 0.5 watt S.A R»=6800 ohms ±5%, fixed film, 0.5 watt Ra«=4700 ohms ±5%.
1 watt R»=0.22 megohm, 0.5 watt
Rai=8200 ohms, 0.5 watt Rm=68000 ohms, 0.5 watt
Rk=8200 ohms ±5%, fixed film. 0.5 watt
Rai, Rm, Rs7=1 megohm, 0.5 watt
R35, R4o=0.18 megohm, 0.5 watt
Rys=0.33 megohm, 0.5 watt
R41, R4», R(4=39000 ohms
±5%, 1 watt R4a=0.56 megohm, 0.5 watt
R15, Rio, Ri7=2.2 megohms,
0.5 watt R<s=0.39 megohm, 0.5 watt Ri», Rai, Roi=1000 ohms,
0.5 watt Ti=Burst transformer, RCA Stock No. 120816 or equiv.
Ti=3.58-MHz oscillator transformer, RCA Stock No. 120815 or equiv.
Yi=3.58-MHz oscillator
crystal
Circuit Description
These circuits extract the color information from the 3.58-MHz chrominance sidebands included in the composite color video signal. The color information is included in the chrominance sidebands in the form of two difference-frequency components that have a phase difference of 90 degrees and that are derived in the color television transmitter by subtraction of the luminance (Y) signal from the red (R) and blue (B) co\or signals. [The green color difference (G -Y) components are not transmitted, but instead, are derived in the color receiver by addition of complements (negative values) of the R - Y and B - signals.] To accomplish the demodulation function, the chroma circuits are required to develop two continuous-wave 3.58-MHz signals that have a phase difference of 90 degrees, each of which much be added vectorially to the chrominance side bands. In other words, the 3.58MHz color subcarrier suppressed during transmission must be reinserted by the chroma circuits before the R- Y and B - Y color-difference information contained in the chrominance sidebands can be detected.
The chroma circuits operate from the color receiver low-voltage (280-volt) power supply. Five 5GH8A triode-pentodes fulfill the electron-tube requirements for the ten chroma stages. The heaters of these tubes are connected in series with those of other tubes in the receiver; operating power for the series-heater string is obtained directly from the 117-volt ac power line.
The input to the chroma circuits is the composite video signal after it has been amplified by the first video amplifier and the sync-age- and-chroma driver (shown on circuits 29-32 and 29-33, respectively), in addition to the chrominance side bands, this composite signal includes the luminance signal (equivalent to the monochrome picture signal in black-and-white transmissions), the conventional horizontal and vertical sync pulses, and the color burst synchronizing signal. The color "burst" is a 3.58 MHz reference signal of approximately 8 cycles that occurs during the horizontal retrace blanking interval immediately following the horizontal sync pulse (refer to Fig. 96, page 73).
The chroma input is applied simultaneously to the chroma band pass and burst amplifiers. When no burst signal is included in the chroma input (i.e., for black-and-white transmissions), the color-killer stage develops, by means of the current through diode CR1, a negative dc voltage across capacitor C- that biases the chroma bandpass amplifier beyond cutoff ; as a result the chroma input is not applied to the color demodulators.
The operation of the burst amplifier is controlled by a gating signal (burst-gate and killer pulse) from an auxiliary winding on the horizontal-output transformer (T1 in circuit 29-33). This gating pulse is generated at the same time and has the same time duration as the horizontal blanking pulse used to blank out the horizontal retrace on the color picture tube. This interval corresponds to the period of the horizontal sync pulse and the 3.58MHz burst synchronizing signal that immediately follows the sync pulse. The burst amplifier, therefore, only amplifies this portion of the chroma input. The primary of transformer T1 in the plate circuit of the burst amplifier, however, is tuned to 3.58 MHz so that only the 3.58-MHz burst signal is coupled from the plate of the burst amplifier.
The separated burst is coupled by transformer T1 to the control grid circuit of a 3.58-MHz injection locked oscillator circuit. The oscillator, therefore, is forced to operate in step (with respect to both frequency and phase) with the incoming burst signal. The 3.58-MHz crystal Y1 is used to assure excellent frequency stability in the oscillator circuit. The oscillator develops the continuous-wave 3.58-MHz reference signal applied to the control grids of the Z and X demodulators. The quadrature network (L3 and Rh) causes a 90-degree phase shift in the 3.58-MHz signal applied to the control grid of the X demodulator. The 3.58-MHz chrominance sidebands must also be applied to the X and Z demodulators before these stages can derive the color difference signals. These sideband signals are obtained from the chroma bandpass amplifier.
The dc bias voltage developed in the grid circuit of the oscillator stage is used to control color-killer action and to derive an age voltage for the chroma bandpass amplifier.
The cathode-to-grid section of the oscillator triode, diode CRa, and associated components from a two diode voltage-doubler circuit. Any dc voltage developed in the oscillator grid circuit is approximately doubled at the voltage-doubler output (anode circuit of diode CR.i). When no color signal is received (i.e., no burst signal applied to the oscillator), the dc voltage at the grid of the oscillator is approximately -5 volts. The -10 volts developed across da and R,.-. in the anode circuit of voltage-doubler diode CRS is reduced to approximately -1.4 volts at the control grid of the color-killer stage. For this low level of bias, the color killer stage conducts and develops a cutoff bias for the chroma bandpass amplifier.
When color signals are being received, the burst signals applied to the oscillator causes the oscillator grid bias voltage to increase to approximately -8 volts, depending on the amplitude of the burst signal.
The dc voltage at the anode of the voltage-doubler diode then rises to approximately -16 volts, and the bias on the color-killer stage is in creased to about -4 volts. For this bias level, no current flows through the color-killer stage, and the cut off bias for the chroma bandpass amplifier provided b the color-killer stage is removed. The grid bias for the bandpass amplifier is then derived from the dc voltage at the grid of the 3.58-MHz oscillator. Because this voltage varies with the amplitude of the burst signal, it provides automatic-gain control for the band pass amplifier.
With the removal of the cutoff bias provided by the color killer, the bandpass amplifier is allowed to amplify and pass the 3.58-MHz chrominance sidebands contained in the chroma input (video signal). The single-tuned transformer T» in the plate circuit of the bandpass amplifier forms a selective load to the 3.58-MHz chrominance sidebands.
The output of the bandpass amplifier, therefore, is a 3.58-MHz signal that contains the R- Y and B - Y color-difference information. The instantaneous phase difference of the 3.58-MHz color-difference components with respect to the burst synchronizing signal defines the color information being transmitted, as indicated by the chart on page 73 in the section Electron Tube Applications.
The 3.58-MHz color-difference signals from the bandpass amplifier are coupled by transformer T2 to the screen grids of the X and Z color demodulators where they are mixed with the continuous-wave 3.58 MHz signal from the oscillator. The color demodulators are essentially synchronous detectors. These types of detectors are phase sensitive, and their output is determined not only by the amplitudes of the two input signals, but also by the phase relationship of these inputs. If the amplitudes of the chrominance and continuous wave inputs to the demodulators are considered to be constant, the input of the demodulators is affected by the phase relationship of the two input signals as follows:
When the chrominance and the continuous signals are in phase, the output of the demodulators is maxi mum in the negative direction. When the two signals are 180 degrees out of phase, the output is maximum in the positive direction. A phase difference of 90 or 270 degrees results in a zero output from the demodulators.
The X and Z color demodulators are biased so that the plate current of each demodulator tube is small during the zero-signal condition. The continuous-wave signal applied to the control grid gates the tube into conduction for the full positive half cycle. During most of the negative half cycle, the tube is cut off. With no chrominance signal applied to the screen grid, the plate current of the demodulator tube consists essentially of 3.58-MHz pulses. A low-pass filter in the plate circuit of the demodulator removes the 3.58-MHz component so that the dc plate voltage decreases below the level obtained when there is no input to either the control or screen grid. The dc level obtained when only the continuous wave reference signal is applied rep resents the zero output of the color demodulators; only changes in the average plate voltage above and be low this level will be passed by the output coupling capacitor to the succeeding stages.
When the chrominance signal applied to the screen grid is in phase with the continuous-wave reference signal applied to the control grid, the demodulator tube conducts more heavily during the periods that the reference signal permits conduction.
The plate voltage of the demodulator then decreases below the zero level, and the output coupling capacitor couples the negative change to the next stage. Conversely, if the two signals are 180 degrees out of phase, the average plate current decreases.
The attendant rise in average plate voltage causes a positive change to be coupled to the next stage. For 90- or 270-degree phase differences, the two signals tend to add together at certain times and to cancel each other times so that the average plate current is essentially unchanged.
In the development of the color difference signals at the transmitter, the phase of the R - Y signal is shifted 90 degrees with respect to the burst reference signal and the B - Y signal is in phase with the reference signal. The B - Y component of the chrominance sidebands, therefore, is in phase with the reference signal applied to the Z demodulator, and the R - Y component is in phase with the phase-shifted reference signal applied to the X demodulator. The output of the Z demodulator then is the detected G - Y signal, and the output of the X demodulator is the detected R - Y signal. These signals are coupled to the B - Y and R - Y difference signal amplifiers, respectively.
If strict consideration is given to signal phase relationships, the outputs of the X and Z demodulators are - (R - Y) and - (B - Y) signals. The positive versions of these color-difference signals results from the inversions provided by the R - Y and B - Y color-difference amplifiers. The G - Y color-difference signal is synthesized by addition of portions of the R - Y and B - Y signals from the plates of the R - Y and B - Y difference amplifiers in the resistor matrix network at the input to the G - Y color difference amplifier. The vector sum of these quantities results in a - (G - Y) signal. This signal is amplified and inverted by the G - Y amplifier to obtain the G - Y signal.
The color difference amplifiers all operate in the grounded-cathode mode with the grid bias taken from the blanker circuit, and only capacitance coupling is used from the out puts of these amplifiers to the picture tube. The dc reference level for the three color grids of the picture tube are established by a clamp diode circuit in the output of each difference amplifier. The outputs of the R - Y, G - Y, and B - Y color difference amplifier are coupled to the red, green, and blue grids, respectively, of the color picture tube.
29-35 PICTURE TUBE AND ASSOCIATED CIRCUITS
For Color Television Receiver Circuit Description
These circuits include the picture tube and associated input-coupling and biasing networks, the convergence board, and the horizontal and vertical deflection coils for a color television receiver. The dc operating potentials for the picture tube are derived from the receiver low-voltage (280-volt) power supply, the B Boost (700-volt) voltage developed by the horizontal-output circuit, and the high-voltage (21,500-volt) rectifier circuit. The 6.3 volt heater power for the picture tube is obtained from a transformer (Ti in circuit 29-29) connected across the 117-volt ac power line.
The 15LP22 color picture tube has a number of unique features.
The phosphor-dot screen uses a rare earth, red-emitting phosphor and improved blue and green phosphors.
------------
Parts List:
C1=0.1 uF. Mylar, 400 V
C1=47 pF, ceramic, 600 V, N7B0
Cj, C», Cs=1000 pF, ceramic, 600 V
Ce, C7=0.16 uF, Mylar, 76 V (part of convergence board assembly)
C«=0.082 uF, Mylar, 100 V (part of convergence board assembly)
Ce=0.27 aF, Mylar, 76 V (part of convergence board assembly)
C1o=180 pF, 260 V, part of deflection-yoke assembly
Cu=3900 pF, part of deflection-yoke assembly
C1a=82 pF, 3000 V, part of deflection-yoke assembly
CRi, CRs. CRa, CIU=Selenium rectifier assembly, RCA Stock No. 120068 or equiv.
Convergence board=RCA Stock No. 120062 or equiv.
Deflection yoke=RCA Stock No. 120890 or equiv.
Li=820 uH, part of net work assembly (RCA Stock No. 120796 or equiv.) with Ri (La-L». La-U) (Vi-U. la-Lio) (Lis-Lu, Lis Lu) =Convergence-coil assembly, RCA Stock No. 121343 or equiv., part of convergence-board assembly Ls=Variable inductor, right red-green vertical lines adjustment, RCA Stock No. 1200S9 or equiv., part of convergence-board assembly
Lii=Variable inductor, right red/green vertical lines adjustment, RCA Stock No. 121443 or equiv., part of convergence-board assembly
Lia=Variable inductor, right blue horizontal lines adjustment, RCA Stock No. 120060 or equiv., part of convergence-board assembly
Lir=120 uH. RCA Stock No. 118246 or equiv., part of convergence-board assembly Lu, Lao=Vertical-deflection coils, part of deflection yoke assembly Lie, Ln==Horizontal-deflection coils, part of deflection-yoke assembly Pi=Connector for convergence board, 8-pin male type, RCA Stock No. 112728 or equiv. (mates with Ji on circuit 26-34) P2=Connector for yoke assembly, 8-pin male type, RCA Stock No. 114767 or equiv. (mates with Ja on circuit 26-34) R1=4700 ohms, 0.6 watt, part of network assembly with L1
R2=0.18 megohm, 0.5 watt Ra=0.15 megohm, 0.5 watt Ri=Potentiometer, video peak adjustment, 0.1 meg ohm, 0.5 watt, part of assembly with Rr and Rs (RCA Stock No. 120811 or equiv.) Rs=5600 ohms, 0.5 watt Ro=12000 ohms, 0.6 watt R7=Potentiometer, red drive adjustment, 6000 ohms, 0.5 watt, part of assembly with Rs and Rs (RCA Stock No. 120811 or equiv.) R*=Potentiometer, green drive adjustment, 6000 ohms, 0.5 watt, part of assembly with Rs and R7 (RCA Stock No. 120811 or equiv.) R»=33000 ohms ±5%, 0.5 watt
Rio, R11, Ria=Three-section potentiometer ; screen-grid adjustments for blue, green, and red electron guns, respectively ; each section : 1.5 megohms, 0.6 watt ; RCA Stock No. 120812 or equiv. Ris=47000 ohms, 0.5 watt
Rn=1000 ohms, 0.5 watt
Ri5=Potentiometer, top red/green horizontal lines adjustment, 120 ohms, 0.5 watt, RCA Stock No. 106320 or equiv. (part of convergence-board assembly)
Rie=Potentiometer, bottom red/green horizontal lines adjustment, 350 ohms, 0.5 watt, RCA Stock No. 116635 or equiv. (part of convergence-board assembly)
Rw=Potentiometer, bottom red/green vertical lines adjustment, 60 ohms, 0.6 watt, RCA Stock No. 105059 or equiv. (part of convergence-board assembly) Ri8=Potentiometer, bottom blue horizontal lines adjustment, 60 ohms, 0.6 watt, RCA Stock No. 105059 or equiv. (part of convergence-board assembly) Ri>, R22=100 ohms, 1 watt, part of convergence-board assembly Rao=Potentiometer, left red/green horizontal lines adjustment, 100 ohms, 0.5 watt, RCA Stock No. 120949 or equiv. (part of convergence-board assembly Ra=Potentiometer, left red/green vertical lines adjustment, 100 ohms, 0.5 watt, RCA Stock No. 120949 or equiv. (part of convergence-board assembly Rna=270 ohms, 0.5 watt (part of convergence board assembly) R»=180 ohms, 1 watt (part of convergence-board assembly) Rz>=270 ohms, 1 watt (part of convergence-board assembly) Rao=Potentiometer, left blue adjustment, 60 ohms, 3 watts, RCA Stock No. 114627 or equiv. (part of convergence-board assembly) R27=Potentiometer, top red/green vertical lines adjustment, 350 ohms, 0.5 watt. RCA Stock No. 116635 or equiv. (part of convergence-board assembly) R28=Potentiometer, top blue horizontal lines adjustment, 350 ohms, 0.5 watt, RCA Stock No. 116635 or equiv. (part of convergence-board assembly) R2fi=82 ohms, 0.5 watt (part of convergence board assembly) R»=4700 ohms, 2 watts (part of deflection-yoke assembly) R.11, Rs2=220 ohms, 0.5 watt
S=Service switch, RCA Stock No. 120838 or equiv.
SGi through SGr=Capacitor, spark-gap, 0.5 pF, 1000 V.
RCA Stock No. 120819 or equiv.
THi=Thermistor ; cold resistance, 1.3 ohms ; RCA Stock No. 120891
See Note on page 726.
---------------
The new phosphors are more efficient and are capable of producing 38 percent brighter highlights than previous color picture tubes. The directly viewed shadow-mask picture tube incorporates a screen with nearly straight sides and sharply rounded corners.
The 15LP22 is designed for operation with the blue gun down. The anode bulb contact for high voltage connection is still located in the top section of the tube. Operation in the blue-down orientation, with respect to the viewing screen, provides optimum compromise of pincushion distortion at the top and bottom of the screen. The tube is equipped with an integral filter glass protective window, sealed to the base plate of the tube with a clear resin. An external magnetic shield is not required on the 15LP22. Another main feature of the color picture tube is an einzel-lens focus system. This sys tem is relatively insensitive to variations of the high voltage so that the tube maintains good focus even with variations in picture brightness.
The focus system for the color picture tube is very similar to that used in instruments equipped with a black-and-white picture tube. Normally, the 15LP22 will have optimum focus when connected to ground potential. However, provisions to change the focus potential are facilitated by a pin connector from pin 9 of the picture tube. The focus selected jumper can be connected to 620 volts, 320 volts, or ground merely by relocating the slip-on connector to the proper stake extending from the circuit board.
A three-position service switch S1 is incorporated into the picture tube circuitry to facilitate receiver setup and adjustment. The NORMAL position of the switch, of course, permits normal receiver operation. With the switch in the SETUP or RASTER position, the video input is disconnected from the picture tube, and the ground return for the age Circuit is opened. Raster height and width and color and background levels can then be more easily adjusted.
The output of the color difference amplifiers are applied to the respective grids of the tricolor picture tube. The luminance signal from the second video amplifier is applied to the three cathodes of the color picture tube. These signals combine to intensity modulate the three electron beams to produce the color image on the picture-tube screen.
The horizontal and vertical deflection coils in a yoke on the neck of the picture tube deflect the electron beams, in response to signals received from the horizontal and vertical output stages, to produce the horizontal and vertical scanning required to trace the image on the picture-tube screen. (These coils are connected in shunt with the respective horizontal and vertical output transformer.) The horizontal output circuit provides a sawtooth current wave form at a frequency of 15,750 Hz to the horizontal-deflection coils, and the vertical output circuit provides a 60-Hz sawtooth current wave to the vertical-deflection coils. The picture tube electron beams are simultaneously deflected horizontally across the screen at a rate of 15,750 Hz and vertically at a rate of 60 Hz.
At the completion of each horizontal trace (end of rising portion of sawtooth current wave), the beam is deflected back to the left side of the screen (retrace) to start another trace period. A positive blanking pulse (included in the video signal) applied to the cathodes of the picture tubes cuts off the picture tube during this period so that the retrace lines do not appear on the tube screen. The picture tube is similarly blanked at the end of each vertical trace period.
Correct color reproduction requires that the three beams of the color picture tubes meet, or converge, at the shadow mask and ex cite color dots of the same trios. The three electron guns of the color picture tube are mechanically tilted toward the center axis of the tube so that virtual convergence is obtained with no external converging force applied. Slight bending of one or more of the beams may be required for exact convergence. The convergence circuit performs this function.
The components on the convergence board shown in the circuit dia gram are mounted on a disk-shaped circuit board with a center hole that permits it to be fitted directly on the neck of the color picture tube.
These components are interconnected in a dynamic type of convergence system. In this system, sine wave currents are used to provide horizontal convergence, and parabolic current waves are used to provide vertical convergence.
The sine waves of current used to provide horizontal convergence are derived from a voltage pulse developed across an auxiliary winding of the high-voltage transformer (T1 in circuit 29-33) and applied through pin 8 of the convergence board input connector Pi. The current through each of the three sets of horizontal convergence coils (L2 and L1, L» and Lw, and L13 and L15) is individually adjustable in both amplitude and phase. The phase of the convergence current is adjusted b the Horizontal Shape control Lc, which resonates with the two 0.15 microfarad capacitors Co and C7 at the line frequency (15,750 Hz). The sine-wave convergence current is produced by ringing this resonant circuit with the pulse obtained from the high-voltage transformer. Potentiometers RJ5, Rio, Rw, Rm, and Rm adjust the amplitude of the sine wave convergence current.
Vertical-frequency (60-Hz) saw tooth voltages obtained from secondary windings of the vertical output transformer (T2 in circuit 29-33), applied through pins 4 and 5 and pins 6 and 7 of connector Pi, are used to derive the vertical convergence-current waveform. Because of the integrating action of the convergence coils, this sawtooth voltage results in a parabolic current wave through the convergence coils. Potentiometer Rn adjusts the amplitude of the vertical voltage parabola applied to the three sets of vertical convergence coils (L3 and LE, L? and Ln, and Li» and Lu).
A vertical-frequency sawtooth voltage from a secondary winding of the vertical-output transformer, is applied across potentiometer RJ7. The sawtooth voltage is obtained from center tapped transformers; the voltage at the center of potentiometer Rn therefore, is approximately zero with respect to circuit ground.
Adjustment of this potentiometer mixes either positive or negative sawtooth voltages with the parabolic convergence voltage and, in this way, controls the shape of the convergence signal applied to the convergence coils.