Guys, here it is, 2018, and my MKIIIs still don't work.
I did accomplish moving, marriage, procreation (twice) and working. Anyone with kids knows how hobby time is pretty scarce. Even worse when you have multiple hobbies.
I'm going to really try to get these going.
To recap, I have two factory wired MKIIIs, a few serial numbers apart. They were bone stock when I received them.
I used them for a few months, sounds nice. Then they did a bit of sparking in the GZ34 and in the KT88s. The tubes were probably original, so like early 1960's original (RCA KT88s, Sylvania GZ34s). The tubes lost their getter, and were obviously shot.
I bought new JJ KT88s and GZ34s. Installed them, biased them, and they played, but then started sparking. I then bought and installed SDS cap boards. The amps have their original bias circuit, which seems to work (see below) but I do have kits to replace them handy.
Maybe we can walk this down from the PT?
Wall voltage: 121.5 VAC across wires
Red Wires:829 VAC across the wires, 415 VAC from each wire to chassis
Yellow Wires: 5.45 VAC across the wires to rectifier
Red/Black: 58 VAC wire to Chassis
Green/Yellow: 0 grounded IS THIS A PROBLEM? Should it be 3.15 VAC?
Green: 6.95 VAC across the wires
Output lug of Selenium Rectifier is -75 VDC to chassis.
Bias voltage at pin 5 of output tubes holds steady at -55 VDC, Bias pot has good range.
If I put in a Rectifier (I have two JJ GZ34s, and a Weber Copper Cap Rectifier)
All give this reading: 392 VDC on the RED wire to the SDS board.
Voltage at circuit board Pin 4: 392 VDC
Voltage at circuit board Pin 5: 367 VDC
Voltage at circuit board Pin 6: 332 VDC
I tried one of the original Sylvania 5AR4/GZ34 and get the same numbers.
A second JJ GZ34 gives the same numbers also.
I have a Weber coper cap rectifier, but I can't get in in the socket. It's got all it's pins, and I think the empty pin holes in the socket have never been used, so it's reluctant to go in.
The amp will sit like this (Rectifier in, no tubes, no hook-ups, pre-amp tube in) with stable voltages.
So far so good? I did the same with the second amp, no different, except the PT red wires are 435 VAC wire to chassis. The rectifier in this one makes 412 VDC.
For second amp:
Voltage at circuit board Pin 4: 412 VDC
Voltage at circuit board Pin 5: 385 VDC
Voltage at circuit board Pin 6: 348 VDC
What should the GZ34 be putting out with these input voltages (415 - 435 VAC to chassis)?
Thanks for the help, I'm glad to be back, and glad you guys are around!
PS, Gonna try to put some power tubes in.