Looking for a Noise Theory...

[Helmholtz]

Chassis is steel; guessing anty sheild I install should also be steel & not aluminum? Or at least magnetic.

As I suspect capacitive/electric and not magnetic coupling, any conductive material should provide adequate shielding.

[Justin Thomas]

A few random observations...

Setting it up to squeal but then setting the guitar across the room (maybe 10' away) & no squeal. I feel like it's ground-related, though, as I can get it to screech by grabbing the tube & then if I grab the strings/controls/bridge it stops. I'm picking up a loud buzz too, mainly through the bridge pickup, that also ceases when I grab the strings. So I still feel like there's something there... And why the pickup transmits more noise when I get my hands near it or grab the bobbin is kinda annoying.

I'm gonna use shielded cable for the Cut control runs; as for the rest of the amp, it's tight & there aren't really any long signal runs due to the tube layout. There's not really enough room to get any shielded wire in there.

Thanks for all the ideas, & some of these I'll have to file for "future use" on build #5. Otherwise, it's clean up my mod-mess & finish the cosmetics for this guy. And explore my guitar wiring & probe my grounds.

Justin

[Helmholtz]

I feel like it's ground-related, though, as I can get it to screech by grabbing the tube & then if I grab the strings/controls/bridge it stops. I'm picking up a loud buzz too, mainly through the bridge pickup, that also ceases when I grab the strings.

Grabbing the tube increases coupling capacitance between the plate and the PU (the human body is a conductor!) while grabbing the strings grounds your body and thus reduces coupling.
BTW, grabbing the other power tube should not produce squeal as its plate voltage is out of phase.

[Justin Thomas]

Ah, that makes sense.

I stuck a bit of insulation in the input jack to defeat the shorting feature, that enabled noise. I also both used shielded wire for my Cut runs, then used regular with a shield of copper tape around it. No success. Put a grounded steel shield between pickup & power tubes, no luck.

I may pull out my Bassman & compare some things, using same speaker. Kinda wish I'd bought a scope way back when I hd money instead of buying more amps...

Justin.

[Pedro Vecino]

I don't know if I understood correctly but I would check the path and physical orientation of the OT input wires. Even disconnecting the feedback lifting a pin on the input resistor to the circuit. Sometimes rare things happen in that area.

[Justin Thomas]

Update.

So I dug my Jet with the crappy Celestion out of the closet & rigged it up with a series of jumper wires & such. Holy $#!+ this amp was brite! After looking at about 4 different tone stacks, and 18 working hours later, I finally got pissed off enough to just make the damn thing a straight-up Fender 50W Normal channel w. a Mid control & permanently set Cut across the PI.

I'll just say I have a useful tone stack with lots of spread & this little tird gets loud AF. Tweaked a few caps but otherwise, yeah. That was easy... Three years later. Oh well, at least I'll get a decent amount of money on this one. If I average it out over the 3 years, I think I'm up to maybe $1.50/hour.

But the damn thing WORKS.

Justin

[Chuck H]

...I'll get a decent amount of money on this one. If I average it out over the 3 years, I think I'm up to maybe $1.50/hour.

I think the most I ever made was about $5/hour. The least I ever made was probably an actual negative figure. It probably averages out to about $1.50/hour. Welcome to the industry! You've made it

[HaroldBrooks]

I've had a few amps for repair where when the shielded back panel is removed they exhibit guitar-specific electrical feedback. One Fender in particular played like a theremin with hand proximity to the output tubes, but only with the volume turned down. Full up or at zero, no noise. With a different guitar, no noise at all.

I also has a standalone tube reverb that did this and I kept coming back to that for ages before finding it was the recovery tube coupling cap at fault. Why that only fed back with certain guitars is a mystery.

Do you have foil screening in the enclosure or back panel?

I like that, and amp that plays like a Thermin ! I could use that at one of my gigs when we are playing the crazy part of Led Zeppelin's "Whole Lotta Love" !

Usually I just get some feedback and harmonics,and run up the repeats and level on my digital delay, and use my whammy bar to warp the sound further.

This would be a step up, no Joke !

[HaroldBrooks]

Update.

So I dug my Jet with the crappy Celestion out of the closet & rigged it up with a series of jumper wires & such. Holy $#!+ this amp was brite! After looking at about 4 different tone stacks, and 18 working hours later, I finally got pissed off enough to just make the damn thing a straight-up Fender 50W Normal channel w. a Mid control & permanently set Cut across the PI.

I'll just say I have a useful tone stack with lots of spread & this little tird gets loud AF. Tweaked a few caps but otherwise, yeah. That was easy... Three years later. Oh well, at least I'll get a decent amount of money on this one. If I average it out over the 3 years, I think I'm up to maybe $1.50/hour.

But the damn thing WORKS.

Justin

$1.50 and hour for doing what you love. Sounds like a fair exchange in my book !

I've run into the same amp tone tuning problems as you before, and I've only just kicked the habit of tuning my project amps with a single Jensen test speaker. I always have to go back and change something later on when I match the amp with a much bigger "real" cabinet that has darker speakers. The single 12" Jensen C12Q on my bench is convenient as it's in a small cabinet with a small footprint, and not too loud for testing, but it also is a bit too bright for a rock amp. So I stopped being a bit lazy, and now hookup the project amp to a Well worn Twin Celestion cabinet, before I consider the tone changes done.

Good Luck with that new Beast Justin !