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Old January 18th 16, 04:09 AM posted to sci.electronics.repair
[email protected] jurb6006@gmail.com is offline
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First recorded activity by DIYBanter: Jun 2012
Posts: 1,635
Default Peavey Classic 60 questions

"With transistor amps, the same idle current always flows in both output devices cos they are connected in series. "

I have wanted to pound a couple of things into people's heads about this for some time.

What you say is true for idle current, the bias, but if there is an offset the current through the outputs is not equal. With no load it should be no matter what.

Anyway, the sledge hammer is to beat it in that :

1. Adjust the bias first, with no load.

2. Adjust the balance/offset next, also with no load.

Do this after having warmed it up a bit, if you can't, recheck it hot.

If the manufacturer starts this **** about taking out jumpers to measure bias current, **** all that. Just do the math and calculate it from the emitter resistors. Take my word for it.

In fact I can adjust it with no spec. II can just feed it with low level program material and watch the waveform at the collector(s) of the voltage amp(s). The ||_||_ in that waveform, produced when the feedback is taking care of the crossover distortion is the prime test point. Adjust bias to flatten that out, done.

However, going farther, that is biasing it harder, does have some merit. First of all it is not that much, and it also gives the amp more low power damping factor. Believe me I know the difference. I am not talking going into class A here, I think that is stupid. If you are going to go class A go all the way and go SE. Then for the most part you only got even order distortion.