6V6 1987 build sounds like a dying fuzz...

[MHProd]

Thanks Phil! I'll swap the primaries and report
back.

I hope that's it! No idea either where it could be coming from...

[MHProd]

Nope...

Reversed the primaries and got the squeal of death.

Any suggestions where to look next?

[xtian]

Do you have an oscilloscope? That would make it easy to find where the signal is going bad.

[MHProd]

Unfortunately no, I don't.

Could it be a bad solder joint? I really don't think it's a wiring error nor a component value error. I have triple checked everything and measured all resistors.

I've never heard that type of screechy sound coming out of an amp before...

[statorvane]

Yes, it certainly could be a bad solder joint. I spent a good while chasing down some hash in a recent amplifier build only to find a couple of weeks later it was the guitar wiring - I had recently replaced the pickups - bad solder joint.

Before that I had issues as well, but it turned out to be the cable wiring, and before that a loose input jack. So your issue may be external.

[RockinRocket]

To determine if the problem is in the preamp remove V1 12ax7- adjust all knobs to 10, still there?
If yes remove V2, Still there? If it goes away then you know its happening around the second gain stage or cathode follower,
If its still present remove the PI V3 and do the same steps.

I would recommend using a attenuator because a bad solder joint at full vol will make you jump a bit

[MHProd]

I tried the same guitar/cables with a different amp through a different cab and it's fine, so not coming from these.

RiR, if I any of the preamp tubes is out, how would I hear the issue? wouldn't the amp just be silent?

[pompeiisneaks]

I tried the same guitar/cables with a different amp through a different cab and it's fine, so not coming from these.

RiR, if I any of the preamp tubes is out, how would I hear the issue? wouldn't the amp just be silent?

Not if the source of the noise is around that tube. I.e. the signal path is still in tact for all other tubes if you start with V1. If it stops with V1, then it means the noise is coming from something connected to V1. If not, and the noise is still there, it means it's originating in a later phase of the amp. If this noise only happens with guitar input, though, and you don't hear it otherwise, it may not help a ton.

~Phil

[MHProd]

Yes, I guess I should have precised that the noise is only there when playing. Otherwise the amp is very quiet. No hiss or hum.

[MHProd]

I'm starting to think something might come from the PI/NFB.

In another thread, I posted about my blackflag 100w that has a weird bias issue: the bias changes when I turn the presence knob.

I played that amp yesterday and with the presence maxed out, I get a little bit of that same screechy sound although a LOT less. Now I haven't fixed that issue with this amp yet but it was suggested I look for leaky caps and into the NFB circuit.

If you have other suggestions, please send them my way!

[pdf64]

...bias changes when I turn the presence knob...

If by ‘bias’ you mean power tube plate / cathode current, this implies oscillation, hence my previous query.

[MHProd]

...bias changes when I turn the presence knob...

If by ‘bias’ you mean power tube plate / cathode current, this implies oscillation, hence my previous query.

I checked with the controls on five and voltage measurements are the same.

[MHProd]

I redid most joints but nothing changed.

2 things I just noticed:
The amp is not as loud as it should be.

When the presence is between 8 and max, most of the screechy sound goes away.

Any chance this could be coming from the OT?

[RockinRocket]

You should post a gut shot photo

[MHProd]

Here are a couple of pics.