Safety Precautions [RCA Receiving Tube Manual (1975)]

Shock Hazard and High Voltage Warning -- Receiving Tubes

Most electron tubes present a shock hazard in use because of the voltages at which they operate. This hazard applies to all applications and is not restricted to high-voltage circuits. There fore, precautions should be taken when servicing equipment in which electron tubes are used.

Some electron tubes, such as high voltage rectifiers and those used in the high-voltage regulators of television receivers, operate with very high electrode voltages. Extreme care should be taken during testing or adjustment of circuits in which such tubes are employed.

Precautions must be exercised during the replacement or servicing of these tubes in equipment to assure that the high voltage output terminal is properly grounded when the tube is being removed from or inserted into its socket or when the top cap connector is being disconnected or connected. The tube and its associated apparatus, especially all parts which may be at high-potential with respect to ground, should be housed in a protective enclosure. The protective housing should be designed with interlocks so that personnel can not possibly come in contact with any high-potential point in the electrical system.

It should be noted that high voltages may appear at normally low potential points in the circuit as a result of capacitor breakdown or in correct circuit connections. Therefore, before any part of the circuit is touched, the power supply switch should be turned off and both terminals of any capacitor should be grounded.

X-Radiation Warning Receiving Tubes

Electron tubes that are operated at potentials exceeding several thousand volts may emit X-radiation. The X-radiation is generated when electrons (or ions) which are accelerated to high velocities impact with high energy on various parts of the tube's structure. Tube types which specify an X-radiation characteristic in their published data are designed and controlled for this characteristic

X-Radiation is measured in accordance with JEDEC Publication No. 67A, "Recommended Practice for Measurement of X-Radiation from Receiving Tubes", and controlled in accordance with JEDEC Publication No. 73A, "Recommended Practice for Quality Control of X-Radiation from High Voltage Rectifier and Shunt Regulator Receiving Tubes". These publications are available from the Electronic Industries Association, 2001 Eye St., N.W., Washington, D.C. 20006.

Operation of these devices above the maximum values indicated in their Maximum Ratings may result in either temporary or permanent changes in the X-radiation characteristic of the tube. Equipment design must be such that these maximum values are not exceeded.

The high voltages associated with these devices result in production of X-radiation which may constitute a health hazard on prolonged exposure at close range unless the tube is adequately shielded. Equipment design must provide for this shielding.

Precautions must be exercised during the servicing of equipment employing these devices to assure that the high voltage is adjusted to the recommended value and that any shielding components are replaced to their in tended positions before the equipment is operated.

Shock Hazard Warning Picture Tubes

The high voltage at which picture tubes are operated may be very dangerous. Design of the TV receiver should include safeguards to prevent the user from coming in contact with the high voltage. Extreme care should be taken in the servicing or adjustment of any high-voltage circuit.

Caution must be exercised during the replacement or servicing of the picture tube since a residual electrical charge may be contained on the high voltage capacitor formed by the external and internal conductive coatings of the picture tube funnel. To remove any undesirable residual high voltage charges from the picture tube, "bleed off" the charge by shorting the anode contact button, located in the funnel of the picture tube, to the external conductive coating before handling the tube. Discharging the high voltage to isolated metal parts such as cabinets and control brackets may produce a shock hazard.

Tube Handling Precaution Picture Tubes

Picture tubes should be kept in the shipping box or similar protective container until just prior to installation.

Wear heavy protective clothing, including gloves and safety goggles with side shields, in areas containing unpacked and unprotected tubes to prevent possible injury from flying glass in the event a tube breaks. Handle the picture tube with extreme care. Do not strike, scratch, or subject the tube to more than moderate pressure. On types having an integral safety panel, particular care should be taken to pre vent damage to the seal area and the edge of the integral safety panel.

Implosion Protection Picture Tubes

Picture tubes which employ integral implosion protection must be replaced with a tube of the same type number or an RCA recommended replacement to assure continued safety.

X-Radiation Warning Picture Tubes

High-voltage electron tubes that operate at potentials exceeding several thousand volts may emit X-radiation.

Operation of a television picture tube at abnormal conditions may produce X-radiation in excess of design limits.

X-Radiation is measured in accordance with JEDEC Publication No. 64C, "Recommended Practice for Measurement of X-Radiation from Direct-View Television Picture Tubes." This publication is available from the Electronics Industries Association, 2001 Eye St., N.W., Washington, D.C. 20006.

For radiation safety when servicing a television receiver, it is essential to ad just the high voltage, using an accurate and reliable high-voltage meter, to the value specified by the set manufacturer following his recommended procedure.

It is also essential that all external shields are properly replaced. In servicing a television receiver that requires a replacement picture tube, a tube with the same type number or an RCA recommended replacement tube type should be used to assure the same or improved integral X-radiation shielding.