Bassman 200 Power Transformer?

[NZimmerman]

I've been working a Bassman 200 problem for a friend. Originally, Output would distort after warm-up. While working the problem the -12VReg blew out. Found the ground Diode D10 blown. Replaced it with a 1N4004 as I do not think a 500mw diode in the ground path for a 1A reg was proper in the first place. Anyway, Q10 and 11 were hot as reported here on an earlier thread. Replaced both and started back at TP1 to see what was up.

The power on TP1 and TP2 of the Amp running @ +/-60V instead of 50V. Seeing a 88VRMS AC input via my fluke meter off the transformer unloaded. seeing 41 VAC on the +/-16V windings. I think I've developed a shorted winding on the primary side of the transformer resulting in High inputs. Opinions quite needed. Thanks in Advance.

[greekie]

Does the power transformer get hot when plugged in with out a load? If not, I don't believe it's shorted.

Remember, the amp is probably not fully loaded. And maybe the voltages were read when everything worked, with 110V line voltage. If your line voltage is above that, that too could explain the higher voltage. As well as manufacturing tolerances.

YM2C

Jake

[Enzo]

It is highly unlikely your power transformer has failed at all. It is EXTREMELY unlikely it has fail so as to work normally but put out 10 extra volts.

Your 1N4004 won;t hurt anything, but that smaller diode was fine. The regulated current does not flow through that leg. The load is connected to circuit common, not the ground leg of the Vreg. That leg is merely a reference. Your diode burnt up when the Vreg burnt up. You sure that is a 12v Vreg? Schematic calls for 15v supplies.

88vAC, or 44VAC to rectify, yields about 60v, so that seems normal. And 20.5 rectified makes about 29VDC, not unreasonable for a Vreg. The test points are indeed marked 50v each, but look right next to the TP boxes, the voltage shown there us 57v each. Obviously they can;t both be right, and 57 isn;t far from your 62.

I think your power levels are fine.

[NZimmerman]

Correct on the -15V reg (not 12). Problem was that the first time I changed the Negative regulator the Diode failed. This gave me -30 and +15 or 45 Volts across the Op Amps on the Preamp board. Made a heck of a mess. I thought I had it all back up and working but failed after a three hour burn-in. Original problem, distortion in the output. I'll take it all back apart and see whats up. Posts questions as I can nail down bad test points. I really appreciate the insight! I'll try to get a fresh post up tomorrow. Thanks again for the comeback...