Hot Rod deluxe intermittent volume loss problem

[Prairie Dawg]

I've got a HR Deluxe in house that's got a strange problem. The owner had an electrician friend do a bunch of Fromel Electronics mods (guy sells kits on fleabay) mostly ill advised stuff of no great value. So he says "Yeah, I was playing it a couple of weeks ago and the volume dropped way down." So I check the bias, usual stuff and find nothing much wrong. Next, I tip the amp on its face and the volume comes back on with some background hash.

So I say "This is good because now we've got a failure mode to think about."

I pull the boards and start cleaning up the mess the electrician made, and I ditch the carbon comp resistors the guy installed. So I put it all back together and get ready for a test. Right away I've got the colume, but after about three minutes it goes away again.

The Volume's weak in both channels so that leads me to think that it's downstream trending toward the phase inverter. I did, of course, resolder all the socket solder joints on the tube board.

Any ideas?

Thanks, y'all.

[Jazz P Bass]

Use the FX jacks.
Narrow it down to Preamp or Power amp.

[Prairie Dawg]

Use the FX jacks.
Narrow it down to Preamp or Power amp.

Not to be a complete blockhead, but that's done by running a cable from the efx send to the efx return, correct? If the problem persists it's in the power amp?

[Jazz P Bass]

Jumpering the jacks will prove or disprove a jack issue.
Inserting a signal into the Return jack will go right to the power amp. Bypassing the preamp.
Using the Send jack to another amplifier (or simply monitoring it) will bypass the power amp.

offtopic.
"Blockhead?"
Isn't that a Charlie Brown term?

[Prairie Dawg]

Thanks for the tutorial. Up until a couple weeks ago I'd never used an efx loop so that's pretty much why I'm such a noob about them.

I cheerfully confess to being a blockhead at times and this is one of them-although I am more of a Linus type person.

[Ronsonic]

Don't know why you ditched the carbon comps, that part of the mod made sense. THe HRDs are chronic for blowing the Plate Rs on the PI stage.

Being that it is an HRD and you didn't mention the subject, I'm going to ask about the quality of the solders and integrity of the ground buss on the preamp section. HRDs come with almost as much bad solder as Crates. People often mod amps instead of repair them. The ground for the preamp section, including the solid state stuff that does the channel switching runs through the wings on the control pots. A bad solder on those will cause all sorts of weird symptoms.

Worse, the Fromel kit includes a replacement MV pot, but does not make provision for replacing the jumper on the ground buss that the original mounting wing provided. Use a wire jumper to complete the ground.