5e3 squeal tone and volume pots

[acjohnson]

This is my first build. For some reason, when the volume and tone pots are cranked up past half way it squeals really loudly. It has EH 6V6 GT power tubes, EH 12ax7 and EH 12ay7 preamp tubes and a GE NOS 5y3GT rectifier. Also, it is distorted even at low volume levels. Help please! Thanks in advance.

[Colin]

You could try swapping the blue and brown wires from your OT to the power tubes over. That might be the cause of the squeeling. HTH
Col

[sportster4eva]

Originally Posted by acjohnson

This is my first build. For some reason, when the volume and tone pots are cranked up past half way it squeals really loudly. It has EH 6V6 GT power tubes, EH 12ax7 and EH 12ay7 preamp tubes and a GE NOS 5y3GT rectifier. Also, it is distorted even at low volume levels. Help please! Thanks in advance.

Sounds like you have a parasitic oscillation problem. The distortion at low levels is the clue to that. It's probably a layout issue. Ground loops or wiring. I don't think reversing the output transformer wires will help, because a 5e3 uses no negative feedback loop. Maybe you could post a pic of the guts, this might give us a better idea of what it could be. Go back and triple check all your connections and layout. Have you tried a different tube in the 12ay7 position?
Keep hunting,
Paul

[Bruce / Mission Amps]

Can you use a couple jumper clip leads to short one or both of the 12AY7 grids to ground?
If no change, try grounding lug number 2 of the 12AX7 with a clip lead.
No change, try using a .1uF +200v cap on one end of the clip, ground the other and then touch the other end of the .1uF cap to lug 7, grid #2 of ythe 12AX7.
This will help isolate the problem to either the input jacks being miswired or the leads from the volume pots to the 12AX7, the signal driving the phase inverter, etc.
Also don't be alarmed if you just happen to have a microphonic preamp tube as this happens too.
The fact that it does it with the volume pots up all the way makes me suspect it is a preamp problem but I've seen some builders forget lead dress and leave many other wires undressed like, output transformer wires much too long leaking/sending audio signal right back into the grids of the power tubes or grids on a previous preamp stage.

[sportster4eva]

Just found this thread over on the FDP forum.. A similar problem, and the OP found the trouble.

http://www.fenderforum.com/forum.htm...-01-2014:18:53

[bichinks]

I’m having a similar issue in a 5e3 I’m building. A strong squeal is produced, even with both volume pots to zero, and increases when dialing the tone pot to the treble side.
Shunting the connections from both .1uF cap that go to the volume pots, decreases the noise a little, but it’s still there.
Shunting lug 2 from second 12ax7 to ground produces perfect silence.
I’ve tried bypassing the volume/tone controls (connecting directly the connections from the .1uF capacitors to lug 2 of the second 12ax7) and the squeal is there (and at full volume)
Any ideas will be appreciated….

Thanks

[TD_Madden]

+1 on what Colin suggested.

[Jag]

No NFB in a 5E3! Swapping the secondaries won't do anything.

You still need a reference to ground for the grid on V2. If you want to bypass the tone and volume controls, you'll need a 1M to ground from grid 2 on V2.

What happens if you ground both grids of V1 like Bruce suggested?

Since it goes quiet when you ground the grid of V2, I'd be looking at what's happening before that. If grounding the grids of V1 stops the noise, check that the input jack grounds are good. If the noise is still there with the V1 grids grounded, try a new 12AY7.

[hasserl]

Originally Posted by TD_Madden

+1 on what Colin suggested.

Since this amp does not use nfb I don't see why swapping the OT wires will help.

edit: Oops, I see Jag already covered that!

[Jag]

I think we both drew the guns at the same time, I just have a quicker trigger finger.