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by Herman Burstein Static Sparks Q. During fast wind on my Ampex 2160, I have frequently noticed a spark jump from the axle to the tape spool or from the spool to the tape or from the surface of the deck to the spool. This appears to me to be an electrostatic spark, and it is accompanied by a characteristic "snap" sound. Is this a common phenomenon during dry winter months and will such a spark degrade recorded material on the tape? -K. W. Dickman, Urbana, Ill. A. The phenomenon you describe is, I believe, rather uncommon, and it may well be cured by grounding the machine. If this doesn't help, try writing Ampex. I doubt that the spark will affect recorded material, however, you are in a much better position than I to answer this question. Using Computer Tape Q. I recently picked up a number of reels of 1/2-in. computer tape from the local salvage yard. More out of curiosity than necessity, I attempted to slit the tape to 1/4-in. width for use with my home recorder. Unfortunately, I could not obtain a uniform cut, and the tape wanders over the heads and will not reproduce accurately. The signal occasionally fades out on one channel or the other. What kind of frequency response could I expect from this rape, assuming I can slit it accurately? Could there be a lubrication problem with consequent head wear? -George B. Moore, Ar., APO, Seattle, Wash. A. If wide tape is to be slit, this must be done very accurately to a nominal width of 0.246 inches plus or minus 0.0002 inch. Otherwise you will run into problems of sticking in the tape guides, skewing, etc., and this would account for your fading of signal. Without some specific information on this tape, I cannot give you definite information on response but you can probably expect somewhat elevated treble and perhaps very low output. It's rather doubtful that computer tape would be rougher on your tape heads than regular audio tape, however, this may be the very reason the tape wound up in the salvage yard. Demag of Cassette Heads Q. My problem concerns the demagnetizing of a cassette-type record/playback head in a General Electric Model M8350A. The external shell of the head is magnetized, and even replacement heads seem to be pre-magnetized. Demagnetizing with a Robins TD-3 head demagnetizer fails to remove the flux in the head. The external shell attracts a steel object. Does some type of head have a built-in magnet that is not intended to be demagnetized? Would a cassette type demagnetizer be more suitable than my Robins unit? -E. L. Freeland, Indianapolis, Ind. A. To my knowledge, heads are not intended to be magnetized, because magnetization is a source of noise and treble loss due to the erasing effect of the magnetized head. It may be that you can achieve adequate demagnetization of your cassette head by using a bulk eraser with a sufficiently powerful magnetic field when brought up within a few inches of the head. I can't comment on the adequacy of the cassette-type demagnetizers as they vary and I haven't a great deal of experience with them. I suggest that you also address your query to the manufacturer of the cassette machine.If you use a bulk eraser and your equipment has a VU meter, be careful not to bring the eraser within about six inches of the meter for the eraser's strong field might damage the meter. Peaking an Erase Head Q. Can the erase head be peaked for maximum efficiency? I noticed that my recorder has a small capacitor in series with the erase head and was curious about whether the unit had, in fact, been peaked. A friend of mine suggests that as the tape moves over the heads, capstan, and guides, static electricity is generated. I agree with him, but he further contends that this charge is d.c. and results in noisy tapes and magnetized heads. His conclusion is that the machine should be well grounded. What is your opinion? -Vincent Mogalero, Woodside, N.Y. A. The erase head can be peaked with a series capacitor. Often the oscillator provides more than enough current to drive the erase head, so that the objective is to limit this current by an appropriate resistor or capacitor. However, when dealing with very high oscillator frequencies, peaking may become desirable because head inductance may be a barrier to sufficient current flow through the head. What your friend may be referring to is that audio signals (a.c.) are asymmetrical. This asymmetry represents a d.c. component, which tends to magnetize the heads. Magnetized heads and other components contacted by the tape tend to produce noise on the tape and to erase the very high frequencies. I doubt that grounding the machine will take care of the problem. The solution is to subject the heads, guides, etc. to adequate demagnetization on a regular basis, though this doesn't have to be done as often as head cleaning. Consult the machine's manufacturer for information on how often this should be done and with what strength demagnetizer if this is not in your owner's manual. (Audio magazine, Herman Burstein) = = = = |
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