Princeton output jacks wiring

[Chuck H]

Turning down the voltages with a variac is also reducing your filament voltages. This could be causing your problem. Set up the amp as you tested it and check the filament voltage.

About the grounding scheme... I usually have my best results using a two star ground system. Grounding everything at the PT bolt on amps bigger than single ended types can cause hum IME. Pehaps it's due the the current being higher, not sure, but in AB1 amps I find that one ground point near the input jack used for all preamp grounds and a second near the mains for all power amp and power supply grounds works for me. In fact on some amps (amps with reverb especially) I use a third ground point at mid chassis for the reverb, PI and presence control grounds. I usually just ground all filters at the PA ground point but if the amp has any hum or oscillations I'll try changing the preamp filter grounds to one of the other ground points. Just something to try if the amp hums when you get it working.

[frankeg]

"Turning down the voltages with a variac is also reducing your filament voltages" Good catch Chuck! Weather or not that is the problem, I missed it. Had to work today so I'll check later. I was reading the "Valve Wizard's" take on grounding and he recommends a chassis ground at the input too. I'll split it like you said. I also think my very cold bias is a contributing factor. I'll change the dropping resistor on that tonight as well. I'll keep you posted. Thanks

[frankeg]

To all who are following my build I'm pretty much finished. A big thank you to those actively contributing and a great big thank you to hasserl who's recommended changes (given to peaveybandit) were used. My problem was fixed with the "correct" rectifier (5U4GB vs. GZ34) and a 100k bias dropping resistor on my Hoffman bias board - I was a little surprised that I needed 100k since I am using an Allen PT with a 50Volt bias tap... I guess there really isn't much current involved. I biased it up last night. It’s a little on the cold side at 19ma and 425 vdc... I am using JJ's but have a pair of EH 6V6's that folks say handle the higher voltages well, that I plan to try. It sounds great! I made recommended changes to the vibrato circuit and it works extremely well... Overall I am very pleased! I don't have a cab yet which I think I'm going to built myself (pine & fabric) but when that's done, I'll post some pics and sound bites...BTW, the Allen trannys are awesome!
I haven’t really opened it up yet but I get the impression that there’s a lot of “beef” in there… I’ll keep ya posted…frank