Tube Amp Archive

I installed a bottom plate last night and it really does make a difference. The noise floor on the amp is really quite good now. There's some hiss at high volume, but nothing more than what you'd expect from a relatively high gain circuit. The amp is very stable and hum free. So I think I'll forego ...

Have you tried using aluminum flashing as shield over the top. It will hum and pick up radio stations if the enclosure isn't completeley isolated. Try grounding the output jacks to the ground in front of the Big Caps. Try grounding a cap to the input jack (not sure what value)? Mine hummed at first...

This evening I figured I should try running shielded cable from the volume pot to the second gain stage grid, to see if that might help. But before I made any changes I decided to do one more chopstick test... Almost every place I touched the amp, it would go "thump" through the speakers, but when I...

Jimy I went over your build, very nice work. :) I didn't notice anything wrong. You must be using the Heyboer 5200 OT with a blue center tap wired to the lower stby switch. At first that threw me but I have not build an express with this tranny but had a wiring diagrahm for it. Just how close is th...

Appreciate all the suggestions. I smacked my head when I saw "microphonic tube." Of course! That must be it! Sadly, though, that was not the case. I've tried swapping out every tube, including the power tubes, and while some of the changes seem to reduce the hum (at least temporarily) nothing elimin...

My just-finished Express has a problem with hum that I can't seem to figure out. The amp works well and sounds great with the volume set at 9 o'clock, but anything beyond 12 o'clock induces hum. Symptoms: When I turn the volume up to 12 o'clock or beyond, the hum starts slowly and builds, so it seem...

My just-finished Express has a problem with hum that I can't seem to figure out. The amp works well and sounds great with the volume set at 9 o'clock, but anything beyond 12 o'clock induces hum. Symptoms: When I turn the volume up to 12 o'clock or beyond, the hum starts slowly and builds, so it seem...

Thanks for the input. I'll cut both leads to V4 length, test, and adjust as necessary.

I recently got the Toneslut OT with blue/green/purple leads and I'm wondering if there's any more intel on this. Is green to V4, purple to V5 working for most people?

Ahhh you must mean Mr. Marshall. If I remember correctly Leo didn't play guitar either. :lol: Jim Marshall was a retired drummer, like you. I think Leo played a little clarinet in High School, but that was about it. He couldn't even tune a guitar and Forrest White (Fender plant manager) tells a sto...

OK... um, power modulation then...

Great looking amp. Can't wait to hear it.

Beautiful work. Nice concept and great execution. Looking forward to the clips and, especially, the schem and layout. I'm very curious about the power control. Can you share your impressions? How does the amp sound and feel when scaled back as compared to full voltage? Also, are you scaling just the...

The "re-forming" of electrolytic capacitors is something that's really only necessary when you're working with old electronics that haven't been used in years. When electrolytic caps sit idle for long periods of time, the dialectric (a microscopic layer of metal oxide) actually breaks down and disol...

Germ Your looking at a pic of a 21 year old original. ok. i still don't like it. bad engineering. germ It may indeed be bad engineering, but it seems to work. I'm reminded of an old engineer friend who used to say "In theory, theory is the same as practice; but not in practice." Sometimes we outthi...

I'm new to the forum but not completely new to amp building (completed 8 or 9 amps). I have a couple newbie type questions and, though I did try searching the archives, I can't find a clear answer. So I'm hoping someone will indulge me: 1.) Why do some folks use "goop" (looks like silicone) on some ...