02-28-2018, 12:44 PM
Ok, so I happen to have a 1973 V-2 in the shop. A typical basement find someone brought me with all the issues you'd expect, but now it's up and running 100% (V-2's actually run with higher B+ voltages than V-4's, about 50v higher). The idle Bias is -68, and when I push my signal right to the clipping line, the crossover looks great, the Bias drifts to -67 due to sag in the supply from the draw down. In order for me to get the bias to -85, I must crank the signal well beyond clipping. That will bring the bias to -85(+/-) due to the screen dropping 100 volts and the plate dropping about 65 volts. This draw down on the plates and screens offsets the bias voltage in those conditions. That's why that Bias measurement seems very odd, that extreme clipping is not a condition used to troubleshoot these amps. The observation about having separate bias voltages at that extreme clipping point may play a roll, but it's not critical enough to solve the issue since we already know one side is Red-Plating and the other is not.
Any luck with the Bias supply Cap and Diode?
Tip to anyone reading this: Anyone working on a V-4/V-series amp should always check their Hum Balance pots, they are super common to blow, sometime you don't even realize cuz of where they short in the winding. Especially if it's original.
Any luck with the Bias supply Cap and Diode?
Tip to anyone reading this: Anyone working on a V-4/V-series amp should always check their Hum Balance pots, they are super common to blow, sometime you don't even realize cuz of where they short in the winding. Especially if it's original.