Recently, there was a rather nasty snap and flash I could see and hear around V7 when the TDR sent high voltage to the rectifier. The amp sounded fine after the snap. For some strange reason, when I replaced the KT 120's with my older Gold Lion reissue KT88's there was no start-up arcing but this could simply be a coincidence. I carefully checked everything visually under the hood and could see no obvious issues. I did, however reflow all the tube socket connections. I checked the tube socket resistors in circuit and found the bias resistors for V2 and V3 were reading a little over 14 ohms, those for V6 and V7 were very close to 10 ohms. The 1 K ohm resistors were all fine right at 1 K. I replaced the bias resistor on V2 with a resistor reading 10 ohms out of circuit and it read 14 ohms in circuit.
Now to my questions. In testing the voltages, with diodes connecting rectifier pins 6 and 7 and 4 and 5, I got the correct 430 VAC before the diodes, but only about 225 VAC after the diodes. I didn't expect this kind of voltage drop. 1) what caused the big voltage drop, just the AC to DC conversion or something else? 2) since I'm using a SS rectifier now, are the "yellow sheet" diodes even necessary or useful?
I removed the "yellow sheet" diodes and moved the AC high voltage transformer leads back to pins 4 and 6. Now with the KT 120's back in the amp, I haven't experienced the start-up arcing and flash over 5 or 6 start-ups. Maybe another coincidence, but perhaps all my tinkering did deal with the underlying problems. I haven't checked any other voltages but perhaps I should. Any insights to this situation would be appreciated!