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A few weeks ago I hauled my Chinese Music Angel 845 off the shelf to A/B against a just completed amp.One 845 failed to light - swapped the 845s between channels and found that it was the 845 which was the problem - so I ordered a matched pair of 845B to get going again.
On the weekend I pulled off the bottom and identified the bias pots and set them back toward their higher bias (less tube current) end before fitting the new 845s.
On the channel which had the bad 845 I immediately noticed smoke from the choke in the HV supply. Taking a closer look I also noticed that the Output Tranny on that side had obviously run hot at some stage and some of the black "gunk" from inside the tranny had started to run down the wires exiting the tranny.
I'm about to embark on major repairs
BUT
Is there any easy way for me to test the output tranny for shorted turns etc. I have a good unit to compare against.
I have an LCR bridge, CRO (with X100 probes), sig. gen etc. and a bullet proof (well short circuit proof anyway) SS Amp I could use to drive the output trannies in reverse.
Aside:
Testing the power supply inductors on the LCR bridge showed that the unit which had emitted smoke actually gave an inductance reading 30% above the unit which had not been stressed, if it had shorted turns it should measure less, shouldn't it???
Maybe still OK and this is just the normal tolerance in the cheap units fitted in the Chinese factory.Edit: I can also borrow a high voltage power supply from work.
All advise gratefully received.
Cheers,
Ian
Edits: 05/07/08Follow Ups:
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