Loud screech when volume is turned all the way down.

[H Chandler]

Loud screech when volume is turned all the way down. And only when there's nothing plugged the into input. With a guitar plugged in, all is well. Turn it down and amp goes silent like it ought to. Pull out the jack, and howls? Turn vol up to about 2 and all is well.

I already changed the switch. No luck.

Is this from bad switched jack or jacks?

What else to try?

Thanks

[H Chandler]

Here's a schematic

Schematic says Bedrock, but has a bunch of mods (mostly post PI)

[mykey]

Loud screech when volume is turned all the way down. And only when there's nothing plugged the into input. With a guitar plugged in, all is well. Turn it down and amp goes silent like it ought to. Pull out the jack, and howls? Turn vol up to about 2 and all is well.

I already changed the switch. No luck.

Is this from bad switched jack or jacks?

What else to try?

Thanks

this is an oscillation caused by the modifications and you will need to remove them or redesign them. there is no installable cure, it's just a really crappy design.

[52 Bill]

...only when there's nothing plugged the into input. With a guitar plugged in, all is well.

This would lead me to believe that the NC input jack contacts are not working. Try cleaning and tightening the input jacks. Sometimes it will take a slight abrasive to clean those switching contacts. I will sometimes use a small strip of 600 or 1200 grit sandpaper with a little Deoxit spray.

I already changed the switch.

What switch did you change?

[H Chandler]

Oops I meant vol pot.

But it's a switch too. It activates a relay that jumps out the 250p cap in the tone stack.

mykey,

Your insight is blinding. Actually, the amp was even more screwed up when wired as in the original, almost impossible to read , schematic. Perhaps you can point out the error of my ways and suggest a workable fix. I promise to try it and report back as to it effectiveness.

I'll get back with y'all when I've given the jacks a thorough going over.

Thanks all.

[mykey]

But it's a switch too. It activates a relay that jumps out the 250p cap in the tone stack.

mykey,

Your insight is blinding. Actually, the amp was even more screwed up when wired as in the original, almost impossible to read , schematic. Perhaps you can point out the error of my ways and suggest a workable fix. I promise to try it and report back as to it effectiveness.

I'll get back with y'all when I've given the jacks a thorough going over.

Thanks all.

I don't think that this is a jack problem, and we don't know what the schematic of the modification is. Actually when the volume is turned down, you almost have an sine wave oscillator circuit. so take out all the modifications and return it to the original design and we can go from there, or draw a new schematic of the modification, otherwise we have no clue of what needs to be fixed. actually I'll look at it some more and come up with an opinion...

[mykey]

Loud screech when volume is turned all the way down. And only when there's nothing plugged the into input. With a guitar plugged in, all is well. Turn it down and amp goes silent like it ought to. Pull out the jack, and howls? Turn vol up to about 2 and all is well.

I already changed the switch. No luck.

Is this from bad switched jack or jacks?

What else to try?

Thanks

see if this is readable, should help solve the problem.

[H Chandler]

What I posted IS the modded circuit

Well not entirely.

There have been other mods after the cathode follower but I really doubt that this would cause this type of problem. Everything to the left of the CF is as shown on the drawing.

[mykey]

Well not entirely.

There have been other mods after the cathode follower but I really doubt that this would cause this type of problem. Everything to the left of the CF is as shown on the drawing.

only happens when the guitar is unplugged?
That's the first stage V1, and nothing more.