Tube amp causing scratching static sound

[Blues Rocker]

I bought a used Victoria 45410 (Bassman) amp recently and was practicing for about 2 hours when it began to get a scratchy, static sound no matter the knob settings or whether the guitar was plugged into the amp or not.

My first guess is that one or more capactors are going. Or perhaps a tube, but I'm not thinking tube(s) as much as caps. My concern is that if it is a cap I believe Victoria uses special "aged" caps and I don't know if they would be inclined to sell me any since it is used. I didn't fine them to be particularly friendly if they find out you bought used.

Any ideas you guitar techs?

I can solder and measure resistance and volts, but how do you measure a component that causes static?

Know of any really good amp techs I could send it to and get a tune up?

I can do some of my own work but I'm not a tech.

[Dave C]

Check the easy stuff first. The most likely cause of noise in a tube amp is the tubes themselves. When the amp is making noise pull the PI tube...this isolates the preamp from the output. If noise stopped when you pulled the PI the problem is in the preamp...if not then it is in the power section. Replace tubes one at a time once which section problem is in has been determined. It could be just a case of dirty or corroded pins and sockets and often can be corrected by removal and reinsertion of the tubes. It could also be a cold solder joint that opens when it has been heated and makes intermitant contact. Those amps also use carbon comp resisters which can be noisy as well...usually the plate load resisters, but none are immune. It can be tricky to determine which are at fault too...at this point it might be time to see a tech. Keep in mind there is upwards of 450v+ inside the amp chassis which could "light up your life"...and not in a good way!Be careful, and take it to a tech if you're not experienced or comfortable working on or around high voltage circuits. Nice amp BTW...worked on a few...Mark builds nice stuff. Good luck.

[Blues Rocker]

Dave,
Thanks for your advice. It makes sense to me and I will start with what you said. I want to make absolutely sure what you mean by a PI tube. Am I correct that you mean the PREAMP tube?

The amp was not noisy while practicing until about 2 hours into practice, then it got that scratchy/static sound. I will careful. I used to built Heathkits and was a ham radio operator so I think I can do the basic stuff on the inside. The cirquit is about as basic as a decent guitar amp can be.

Thanks,

Scott

[Dave C]

PI stands for phase inverter...it's the preamp tube closest to the power tubes. It's job is to invert the signal and send it along with the original to the power tubes providing the push/pull element to an A/B type power amp.

Guitar amp audio circuits are pretty simple being ancient ,dinosaur technology, but it still works and sounds best at least for guitar use. There is usually enough juice present in them that they shouldn't be taken lightly though.

[siore]

Nice tip with the phase inverter Dave C. I'll take note too.

[Blues Rocker]

Dave C: "It could be just a case of dirty or corroded pins and sockets and often can be corrected by removal and reinsertion of the tubes."

Problem solved!!!
I owe you a great sense of gratitude, Dave, for your input. I pulled each (cold) tube out of it's socket, and carefully reinserted them one at a time. Then I turned the amp ON, waited a few minutes, standby to ON, waited a few more minutes. "What's this?...
no scratchy, crackly static noises...GONE!
O.K., this couldn't be such an easy fix...I'll let it sit powered up on Vol. 4/12 (each channel) for a while. 2-1/2 hours later...still quiet (for a tweed...my blackface is dead quiet).

Played some tunes and got my amp back. Dang, I LOVE THIS BASSMAN!!!!
This is tonal heaven to me. I don't need to look any further...EVER! Done! Completo!

My ES-339 arrives Monday and I cannot wait to test it through the Vicky! (I also have a Victoria Super 35210).

Anyway, thanks for the help Dave...you saved me a major moola!

[Dave C]

You're welcome! I'll take an easy fix over a difficult repair anytime too! Glad to hear it worked out as well and easily as it did. You might want to try some Caig Labs Pro Gold on the tube pins to maintain good contacts...good stuff and high temp so you can use it on the power tubes too.

[axepilot]

I will file this in my archive of tried and true wisdom...........

[Blues Rocker]

Thanks Dave, I'll check it out.

[guitar_randy]

Sounds more like a cap than a tube

[Blues Rocker]

Originally Posted by guitar_randy

Sounds more like a cap than a tube

Randy,
See above...it was just corroded tube pins. Problem was solved immediately by pulling and replacing same tubes.