Quote:
Originally Posted by earlyfilm
Exactly!
What I think is happening here is electrically the same thing that motor-boating is to a vacuum tube audio power amplifier, and the same checks will usually work. In both cases, for pre-1960's equipment, it is most likely in the output stage, but can be anywhere in a related circuit.
The problem here is this Delco Auto TV is probably a proof of conception prototype, most likely done to threaten GM's auto radio suppliers against overcharging for sets and/or to determine if the public would buy one if GM offered a car TV for sale. This prototype only had to work well enough for display and there is no known documentation on the set, including what voltages the missing power supply provided.
Since this spurious signal is probably happening in the vertical output area, the scope will be of little use here. If Bob cannot localize the problem, he may have to find a TV restorer locally who has a scope and is familiar with the older vertical circuits, but that is the last resort.
Bob, I forgot to mention earlier, if there is an electrolytic across the cathode resister of the vertical output tube or in the plate circuit and/or screen grid of the vertical output, make sure they are good. This test can be made by simply jumping them with a second electrolytic, since over capacity here should not do any harm.
James
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The General always built their own radio's since 1946.
All GM cars, with factory installed radio's, were Delco built.