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Old 7th Feb 2023, 10:51 pm   #13
samjmann
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Join Date: Feb 2014
Location: Nottingham, UK.
Posts: 645
Default Re: Sony-STR3800L. Output transistors.

Thank you both for the replies. I made up a four diode string, insulated it, and mounted it on the original tag. Using a lamp limiter gingerly switched on. Both stages now had exactly the same voltage across the bias diode. Removing the limiter the quiescent current did indeed set to 50mv across the emitter resistor test point.

I left the amp running quite loud for an hour and re-checked the quiescent value. It had dropped from 50mV after 5min cold, to 42mV warm after been driven. Both channels reacted the same. So pronounced fit!

Output stages really can be 'fun' SJM.
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