Thanks for the
'interesting' (and confusing) voltage measurements.
Oh, trust me, if there is incompetence to be had, I will fully accept responsibility. I agree the reading is odd, which is why I tested it three times in a row...I had the amp plugged into the DBT, with a 100watt bulb. The bulb stayed dimly lit, and never wavered from that brightness the entire time. The only exception to note is that I am using a cheapy $30 multimeter from Home Depot (home improvement chain). I actually have two of them. Also, the electricity here runs a little high, at around 122V.
I did measurements again, This time with the other multimeter and the results are the same. Tried the DBT on a different power outlet - again, the same. Checked the DBT, and it is working fine. I checked the voltages on the power outlets that are built into the amplifier and they read at about 102 volts or so, I am assuming, due to the DBT.
The maximum AC voltage from the secondary winding on the transformer is <100V (RE - RE). That suggests the 128V AC must be coming from an external source (nothing but the bulb limiter should be connected to the amplifier).
Or it's a 'ghost' reading.
Didn't know a ghost reading was a thing, but that wouldn't surprise me.
Can you measure the AC voltage at the smoothing/reservoir capacitors?
Using the reference point, on the smaller of the smoothing caps that is closest to the main amp board one leg measure the 128Vac and the other leg measures the 75Vac. On the larger cap closest to the main amp board one leg measures the 75Vac and the other leg, which has all the ground wires connected to it, measures nothing.The others measure nothing on AC.
I'm assuming (dangerous) that the 'Auto Class A' switch was OFF: i.e. the amplifier was in Class AB mode.
Yes, the Auto class A switch was off.
Whilst on the bulb limiter/tester, measure the plus & minus ?X/?P DC voltages with the 'Auto Class A' switch ON. The measured DC voltages should be within 1 volt of the voltages measured on the 33000µF capacitors.
I just finished testing them. All the ?X/?P voltages drop about 1 volt when Auto A is turned on, and they are all still within 1 volt of the 33000 caps.
Also, don't forget to measure the plus & minus 22 volt rails - they're critical to the correct operation of the amplifier.
Sorry about that, I took the measurements with the others before and wrote them down, but I forgot to post them. 22+ is 21.5Vdc, 47.1Vac. 22- is 14.5Vdc, with no AC present.