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Okay, so I got the bias issue worked out with this thing. It appears to have been the crappy JJ power tubes I was using, I put the old GEs in and all has been well ever since.
Except of course the nasty hum when the reverb is turned on. It does hum a little all the time but it's not really bad until the reverb is kicked on. What's weird is I first noticed it doing this after I rebuilt the bias supply and recapped it. I figured maybe one of the filter caps I used was bad so I went back through and replaced most of them with Sprague Atoms with no improvement. I started digging around and I think I have it narrowed down.
This is the schematic for the Gibson GA-35RVT which is closer to my amp than the actual GA25RVT schematic on the internet.
http://www.guitar-parts.com/images/ga35rvt.jpg
So I think it's either R49 (220K) or C29 (.001uF) that's giving me crap. I removed the wire from the reverb tank (it's hardwired) from the junction of those components and the hum remained. I put that back and removed the wire from the grid of V3A. The hum is gone. Unfortunately, this kills the reverb signal too. Is this a reasonable assumption based on the testing I've done?
What I don't understand it how either a capacitor or a resistor positioned in the circuit like these can introduce so much hum, and still seem to function otherwise normally as well. The reverb still sounds great besides the hum. It also seems like a really weird coincidence that the hum started right after I did some major work on the amp, even though I was nowhere close to those components. This amp's poorly laid out and kind of a bear to work on, and those components are in a particularly bad spot so I'd like to make sure that there's nothing else I should be checking before I try and dig in.
You guys have come through for me in the past and I really appreciate that, hopefully this can be the last time and I can sell this thing and move on to some other projects I've been meaning to get to.
Thanks in advance.
-Darren
Except of course the nasty hum when the reverb is turned on. It does hum a little all the time but it's not really bad until the reverb is kicked on. What's weird is I first noticed it doing this after I rebuilt the bias supply and recapped it. I figured maybe one of the filter caps I used was bad so I went back through and replaced most of them with Sprague Atoms with no improvement. I started digging around and I think I have it narrowed down.
This is the schematic for the Gibson GA-35RVT which is closer to my amp than the actual GA25RVT schematic on the internet.
http://www.guitar-parts.com/images/ga35rvt.jpg
So I think it's either R49 (220K) or C29 (.001uF) that's giving me crap. I removed the wire from the reverb tank (it's hardwired) from the junction of those components and the hum remained. I put that back and removed the wire from the grid of V3A. The hum is gone. Unfortunately, this kills the reverb signal too. Is this a reasonable assumption based on the testing I've done?
What I don't understand it how either a capacitor or a resistor positioned in the circuit like these can introduce so much hum, and still seem to function otherwise normally as well. The reverb still sounds great besides the hum. It also seems like a really weird coincidence that the hum started right after I did some major work on the amp, even though I was nowhere close to those components. This amp's poorly laid out and kind of a bear to work on, and those components are in a particularly bad spot so I'd like to make sure that there's nothing else I should be checking before I try and dig in.
You guys have come through for me in the past and I really appreciate that, hopefully this can be the last time and I can sell this thing and move on to some other projects I've been meaning to get to.
Thanks in advance.-Darren
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