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  1. F

    1970 Delco Radio Repair - audio distorted

    Thanks for the tip...makes sense. The collector has been reading about 7v with a 11.78 supply. So a little on the high side for your guideline. Although it's been that way since the beginning and I don't think it has changed with the recent drop in gain . I believe the "no-emitter-resistor"...
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    1970 Delco Radio Repair - audio distorted

    Ouch... Old resistor colors (and old eyes) led me to think a 5.6 ohm resistor was 560 ohms. So the 5.6 ohm resistor explains my low reading to ground in the feedback circuit. Having an accurate schematic would really help, but I do not have one. Worse yet, somehow the gain of the circuit seems...
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    1970 Delco Radio Repair - audio distorted

    Quick update: I haven't spent much time but I think the problem may be that the negative feedback circuit is not providing enough feedback. This would explain why I seem to have plenty of volume and lot's of distortion at high volume. Again, I don't have the exact schematic, but I have one...
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    1970 Delco Radio Repair - audio distorted

    I have tried a couple of different speakers with no improvement. The schematic I have for another very similar radio specifies a 10 ohm speaker. If I can find a 10 ohm resistor I might try that as well. I have injected a modulated carrier with a1khz sine wave via the antenna and a 1khz audio...
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    1970 Delco Radio Repair - audio distorted

    The model number is not on the radio, probably a sticker has long been gone. I have a Sams schematic that's very close for a 1972 F-85 Olds. model 23afp1. I'll have to give the car battery a try at some point. Thanks
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    1970 Delco Radio Repair - audio distorted

    Thanks..like another poster said these were never claimed to be HIFI.
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    1970 Delco Radio Repair - audio distorted

    The bench power supply I am using is very stable, but at some point I'll probably have to try a car battery. Thanks
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    1970 Delco Radio Repair - audio distorted

    Yes, it does clip at high volumes at about 6-7 volts, the output stage has a 11.7v supply. The filter cap measures 2300uf disconnected. The value markings are not visible. I have paralleled a 4000uf cap and the ripple reduced maybe 40%, but it didn't seem to help the distortion. The volume...
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    1970 Delco Radio Repair - audio distorted

    I'm trying to repair a 1970 GM am/fm car radio that plays pretty well on both bands, but the audio distorts at high volume levels. I have two questions: 1. Could this distortion be normal? It sounds pretty good at moderate volume but when volume is at the top say 15% of it's range it distorts...
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