The Amp Garage

To me, touch sensitivity is dynamics. A lot of SRV's stuff is very dynamic. For instance, I think "Lenny" has a lot of good examples of touch sensitivity.

Well, I actually just made some good progress! I replaced all those old green Micamold Tropicaps with new Mallory 150's, and the problem is essentially gone. I get just the slightest hint of an oscillation trying to start when both volumes are cranked and the bass control is all the way up, and I hi...

Thanks Ian, no those 150 volt caps are filters for the bias supply and the filament lift circuit. Turns out one of them was in backwards (I should know better) and it did blow the end out of it. It has been replaced - actually everything worked OK without that cap in the circuit at all.

I used a 6.8k tail resistor because I was following the "Modernized 5F6A" layout I found in one of my searches. It was posted on TAG by Martin Manning I believe. Tom, I have been suspicious of the coupling caps because they are old Micamold Tropicaps I salvaged from an organ. I tested them all for l...

Hi Littlewyan, I pulled the output tubes and followed signal through the amp with the scope and never did see any motorboating up through the PI. I guess that doesn't tell me much, since it is likely a feedback/oscillation involving the output stage. The motorboating is tough to see on the scope - I...

Well, here's a little update for anybody that cares...... I tried most of the things you guys suggested, except for Reel's suggestion of grid stoppers on the PI - I was saving that for last. I think I have the oscillation minimized to the point that I can live with it now. The thing that seemed to m...

Well, I got back into this thing and I'm still stumped. I re-flowed the solder joints for the filter caps. No difference. Then I tacked on an extra filter cap per Leo's suggestion. No difference on B+1 or B+2, but it did reduce the severity of the problem with the extra cap paralleled with B+3. So I...

Wow! Gorgeous! I feel like such an amateur when I see the beautiful woodworking some of you guys do!

I have a tube that looks like that, but the writing is almost entirely worn off. I popped it in an amp once and it seemed to be dead, but I couldn't bring myself to toss it.

Thanks Mark. This is the chassis and transformers I got from you a couple years ago. Took me this long to get around to building it. I'll dive back into this thing when I get back from vacation.

I do have a scope and that's the next thing I will look at. However, it will be a few days before I get back to this, since we are going on a quick family vacation for a few days. There will be no tinkering till we get back. Thanks for all the help guys! I'll either figure this out or end up living ...

Thanks TT, those are good comments. I actually followed (somewhat) Martin Manning's "Modernized 5F6A Bassman Build Guide" (THANKS Martin!). Which is actually pretty close to the original Bassman layout, I think. The grounding scheme seems different than the star grounding I've used in other builds, ...

I figure that posting a gut shot here on TAG is like "Go cut yourself a switch" and I think I am man enough to take all the constructive criticism you guys can dish out. Maybe even a little bit of ridicule. This is how we learn. I was getting pretty good at making Champs look tidy, but this one kept...

Ugh - couldn't get the photo to attach.

Against my better judgment, I will post a couple pics. I am particularly bummed about the OT secondary routing under the board. This was something that made sense as I was mounting the transformers, but once I got the rest of the stuff wired up underneath, I realized I should have done that differen...