Volume going up/down.... bad tube?

[Scott Peterson]

I am a little befuddled.

My VHT Pittbull 50/ST head (tube rectified, EL34's output) sounds great... but it has started to do something wierd.

The volume will just "go away" down to almost a whisper and then surge back up and it does this till I shut it off in fear it is about to blow.

Bad tube? Bad rectifier? Initial things to check?

[RL in Fla]

Recto first Scott , since there's only one of em , if not that a tube at a time from V1 on up .

[Scott Peterson]

Originally posted by RL in Fla
Recto first Scott , since there's only one of em , if not that a tube at a time from V1 on up

I figured as much. Gotta wait till tomorrow to fire it up and have at it.

Thanks!!!

[RL in Fla]

Somebody will chime in and tell me I'm full of crap (BIG news flash there :D ) , but that's what I'd guess .

[Southbay Ampworks]

Originally posted by RL in Fla
Somebody will chime in and tell me I'm full of crap (BIG news flash there :D ) , but that's what I'd guess .
You're full of crap RL! (Feel better?) :D

Actually, tubes are a good place to start. It gets more expensive if it's not that. I have a Studio 15 doing the same thing. Works great for 5 or 10 or even 30 minutes, then it starts doing an elevator volume thing, but then it goes down to a whisper, then nothing.

I shut if off, it cools off, then it's fine the next time I fire it up...for 5 maybe (wait this is a repeat, huh?) 10 minutes then the same thing happens again.

Swapped all the tubes. That wasn't it. I'm at the more expensive fix. Good luck, Scott! (RL, you're not really full of crap...)

[RL in Fla]

Big news flash !!! Film at 11:11 !!!!!!! :D :D :AOK


Yours may be a solder joint -
heating up/losing contact/cool off/ ok again Jim .
Not you , the amp . :D :D

[VaughnC]

Yup, most likely a tube or solder joint. Also, if you have a bias probe that also displays the plate voltage on the output tubes, if that voltage lessens with the corresponding volume drop, the rectifier tube would be a good suspect.

[Scott Peterson]

Well, you were right. Thus far, no more volume swells by itself; rectifier tube.

Thanks!

[RL in Fla]

Right 1 Wrong 5,732,435

:D