is it possible? 2nd and last about the ampeg 350H

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pucho812

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O.k. this is the last thread on this topic. But I am sctraching my head on this one. That ampeg I am working on, I got a schemo... I tested it. the pre amp works great. The power amp has issues. It's noisy as well as triggers the limiter to over limit. That causes the sound to drop out. I used a scope on the power amp online and it has noise as stated before. I ran a scope accross the power amp and it is bad at all points. Meaning I get my test sine wave with noise at all point testing There are 2 resistors in it that get super hot. I would imagine they would burn up if they were not 10W ceramics. Anyway this has lead me to a bad transistor or bad transistors. Anyway when testing out the transistors, I found 11 that are acting dodgy. I do not have a transistor testor so I been testing them via the diode checker method with my multimeter.
you test like this. By using a diode tester on a multimeter, when you run your tester leads accross the transistor you should get these results

The base-emitter (BE) junction should behave like a diode and conduct one way only.
The base-collector (BC) junction should behave like a diode and conduct one way only.
The collector-emitter (CE) should not conduct either way.
Either my testing is dodgy or there are actually 11 transistors that need to be replaced.... Or am I tripping and only have one bad trasistor which happens to be the first one and is messing it up for the rest of the circuit?
 
Are you testing the transistors out of circuit?

I'd imagine in a power amp if a situation causes one transistor to go it might take many more with it, and rather quickly.
 
Did u check the power xfmr output, or power regs. Maybe bad power caused all the transistors to blow.
-just a guess...
 
What are the part numbers and what kind of transistor(s) are they?

mosfets, BJTs, darlingtons, transistors with internal diodes?

What does the power amp power supply waveforms look like?
 

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