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first post!
I'm a tube guy not too good with solid state and this fender power amp (which is part of the solid state super showman series from the late-60's) is driving me nuts...
this unit is 2X70 watts and only one side has a problem
ok its been working forever fine till the other day, it popped the circuit reset and shut off...opened it up and immediately found one of the 2N3772 power transistors shorted from C to E and replaced both with NOS RCA's
also one of the TO-39 2N5322 trannys on the main board for the bad channel was shorted, so replaced that as well as the other two of those, as well as the 10 ohm resistors in that area, reason being everything in that area was getting really hot
at this point the amp would stay on with a hum and in addition to the part of the board that getting hot also the two new power trannys and the heatsink would get hot really quick so its drawing major current somwhere
I found a "stabistor" diode connecting the two 3772's that looked supect so I removed it and it doesn't get hot at all...replaced it with an NOS and it still does get hot so its not that
I can't figure this out, its got two identical power amps sides so you'd think it'd be a breeze...I've made countless ohm meter comparisons from side to side and found nothing else "wrong"
I checked the filter caps (4) X 3000 uF and they also seem to measure ok and consistently
the one difference when I measure one side of the filters there is continuity from can to the B+ (out of circuit) and on the other side there isn't...I thought because the two sides are opposite polarity this would be right but I don't have enough experience with can caps to know one way or the other, bit it seems unlikely that both filters would go at the same time out of the blue?
sorry for the long winded post but I've seen some incredible solid state knowledge here and would much appreciate any input
thanks in advance!
Ammscray
I'm a tube guy not too good with solid state and this fender power amp (which is part of the solid state super showman series from the late-60's) is driving me nuts...
this unit is 2X70 watts and only one side has a problem
ok its been working forever fine till the other day, it popped the circuit reset and shut off...opened it up and immediately found one of the 2N3772 power transistors shorted from C to E and replaced both with NOS RCA's
also one of the TO-39 2N5322 trannys on the main board for the bad channel was shorted, so replaced that as well as the other two of those, as well as the 10 ohm resistors in that area, reason being everything in that area was getting really hot
at this point the amp would stay on with a hum and in addition to the part of the board that getting hot also the two new power trannys and the heatsink would get hot really quick so its drawing major current somwhere
I found a "stabistor" diode connecting the two 3772's that looked supect so I removed it and it doesn't get hot at all...replaced it with an NOS and it still does get hot so its not that
I can't figure this out, its got two identical power amps sides so you'd think it'd be a breeze...I've made countless ohm meter comparisons from side to side and found nothing else "wrong"
I checked the filter caps (4) X 3000 uF and they also seem to measure ok and consistently
the one difference when I measure one side of the filters there is continuity from can to the B+ (out of circuit) and on the other side there isn't...I thought because the two sides are opposite polarity this would be right but I don't have enough experience with can caps to know one way or the other, bit it seems unlikely that both filters would go at the same time out of the blue?
sorry for the long winded post but I've seen some incredible solid state knowledge here and would much appreciate any input
thanks in advance!
Ammscray