5e3 Feedback when tone pot is turned up

[Javabirds]

This is my 3rd amp build, my 2nd 5e3. (the other was a new fender Champ to 5F1). I am moving this thread from:

5e3 Troubleshooting

If you follow that link, you will find pictures, voltage readings, and the overall troubleshooting time-line.

My problem is that in either channel the amp squeals when the tone pot is cranked. The input section all seems to jive via resistance checks. There seems to be some interaction between the volume and the tone pot as well. I am using a poly-glut of layouts and diagrams. But started with the one that Mojo includes in their "small parts kit".

Here is a photo of the tone pot:


I need some advice on how to rewire it. I think... Anything to kill the squeal!

[loudthud]

It's been a couple of weeks, did this ever get fixed?

I can't really see the wire that goes from the pots back to the 12AX7 (the 2nd preamp tube pin 2). Is that a shielded wire that goes through two holes in the eyelet board next to the orange cap at the right of the photo?

There are quite a few wires stuffed between the board and the chassis. What are all those? You probably have some kind of parasitic feedback from all those long wires. Shorten up any excess wires and keep the input jack wires, the pot wires and the output tube wires away from each other as much as possible.

[Javabirds]

Thanks so much for looking and asking. I put the project on hold while I waited for an NOS 5y3. I was a little worried about the way higher voltages that the Sovtek rectifier was producing. Now that I have swapped the rectifier I am back troubleshooting this problem.

Right now the amp will feedback when any of the pots are turned up more than 3/4, but only during the first 5 minutes of warm-up. After that, it plays great and sounds good. I think you are right about the wires stuffed behind the board though. They are all ground wires..... The end in a star ground. Honestly, the grounding part of this design has me a little confused. Especially after reading all of the forum posts about grounding! No one seems to agree and so I feel like it is clear as mud. I ran the ground wires on the fender layout to a star. Also I am confused about grounding the inputs and the pots. I don't have the brass plate. Obviously what I did isn't right, so I am ready to try something else. My next plan was to try the grounding scheme found in the Tube Depot 5e3 instructions that uses a bus wire. I do appreciate your help and any advice you can give.

and yes, that is a shielded wire going through the tag board and it is grounded on the tube side.

Thanks!

[Boxnix]

Mine feeds back when the tone knob is cranked and it's really loud because you are jacking a certain frequency range way up and it makes that frequency feed back. I saw from your other thread you have 12AX7's in V1 & V2, that will give you higher gain than original design, making it more prone to feedback. I'm no expert though, I dunno what all can cause feedback. I thought grounding was more about overall hum and noise not feedback, but again, I'm a noob.

Are you using singles or humbuckers? How much clean headroom do you get? Mine starts to OD at about 6 depending on pups and which input I'm in. If you are getting OD at 3 or 4 thats a good sign your preamp signal is kinda huge.