Of course it drops drastically.
You're using a small 40 watt lamp -not a good choice for safe testing for a 150 watt rated amp.
40 watt lamps are suitable for small table radios testing.
With an amp that size, a 75 to 100 watt safety lamp is a better choice.
That is what I always used in the shop when servicing hefty amps.
Thanks for the advice. I was initially using a 100w bulb, but it wouldnt come out of protection and the bulb was always dark. Then one day I started to smell smoke!
Although this unit finally passed the bulb test after i replaced Tr2 Tr4, B+ was still off by 6V. After removing it from life support finally came back to normal -34v.
To continue the puzzle I couldnt get any measurements across Tr2,Tr4 emitter resistors. Traced part of the problem back to bias transistor Qe8, I had E and C leads swapped. Explains why those readings were wonky. Still nothing on emitters although I was getting readings measuring those two points against ground. Replaced emitter resistors, still nothing. Emitter of Qe12 was reading low at -.25V (-0.6v), base measured low at .8v (1.1v)
Replaced drivers Qe11, Qe12 which put those voltages at the proper place and I was finally able to get bias to Tr2,Tr4.
Maybe I cooked those drivers while I had output collectors disconnected, may have left it on too long while taking measurements.
Right now I got 200mV across emitters on both channels with bias pots centered, waiting to get warmed up and dialed in.
Although this unit finally passed the bulb test after i replaced Tr2 Tr4, B+ was still off by 6V. After removing it from life support finally came back to normal -34v.
To continue the puzzle I couldnt get any measurements across Tr2,Tr4 emitter resistors. Traced part of the problem back to bias transistor Qe8, I had E and C leads swapped. Explains why those readings were wonky. Still nothing on emitters although I was getting readings measuring those two points against ground. Replaced emitter resistors, still nothing. Emitter of Qe12 was reading low at -.25V (-0.6v), base measured low at .8v (1.1v)
Replaced drivers Qe11, Qe12 which put those voltages at the proper place and I was finally able to get bias to Tr2,Tr4.
Maybe I cooked those drivers while I had output collectors disconnected, may have left it on too long while taking measurements.
Right now I got 200mV across emitters on both channels with bias pots centered, waiting to get warmed up and dialed in.