That set of tubes will bias in another amp just fine and they also check out OK in my tube tester. (B&K 747B)
I have a set of Valve Art KT-88's that will bias up in the flukey amp.
I thought at first that my GZ-34 rectifier was getting weak because there is only 325 VDC at rectifier pin 8 to ground with the amp up and running. Should be about 435 volts?. I ordered up a GZ-68 copper cap but the B+ remains at 325 V with either.
Another weird thing going on here is with the power supply choke on the under side of the chassis. When I install the bottom part of the chassis the choke is rattling the hell out of it. It seems to be acting like an electromagnet. Remove the bottom portion of the chassis and the buzzes and rattles disappear. Could it be that in the B+ circuit that something is drawing a lot of current thus making the choke behave that way?
B+ winding of transformer measures 762 VAC (!!) without tubes installed. Pin 8 of rectifier to ground is 505 VDC w/o tubes installed.
With all tubes installed, B+ xformer out measures 750 VAC and pin 8 is at 325 VDC to ground. My line voltage here is 117 volts.
I measured the drop across the 2.2k resistor between the last two sections of the can cap at 28.8 V. I believe that would mean that the driver board is drawing .013 amps.
I also checked out the bias supply circuit. Pulled all the tubes and fired it up. Bias tap gives 57.7 VAC and rectifies out to 77 VDC. Checked at pin 6 of each output tube socket while turning the bias pots and measured -28 to -54 VDC. Checked out all the 10 ohm cathode resistors too.
Something is amiss here and I'm having trouble putting my finger on it. Could it be that the PA-060 is getting tired? Output transformer problems? Don't know what to check next. Any and all help and instruction will be followed completely, carefully and will be greatly appreciated.