Giutar amp in old radio cabinet?

[nensign]

Hello,

My wife wanted a guitar amp built into an old radio cabinet so I tried. There was a pretty annoying buzzing noise. I ran the input, volume and power on/off out of the chassis to the front of the wooden cabinet. For the volume and input I used small coax with the shield grounded to the chassis. Of course the power was twisted. When it didn't work I modified it several times including making a shield from half inch coax for the outside wiring. Disconnecting the magic eye tube made no difference.
My question is: Is this possible to do?
I made this same amp a few months ago with everything mounted in the chassis and it worked awesome!

[Helmholtz]

Can we see a picture of your wiring?

[nensign]

It said I've exceeded my upload quota.
It's wired just like the schematic except the extensions to the front of the radio cabinet.

[Helmholtz]

It said I've exceeded my upload quota.
It's wired just like the schematic except the extensions to the front of the radio cabinet.

Wondering if some ground wire is missing.
Are you sure the input jack is grounded as it's not mounted to the chassis?

E.g. if the only connection between input jack and chassis is via a coax cable with shield only connected at one end, there is no connection between jack and amp ground.
Also the pot shell should be grounded.

[nensign]

I ran a ground wire for the input jack and the pot. Separate for each so I wouldn't create a ground loop.
I've attached a pic of the wiring inside the chassis but had to delete the cabinet pic to make room.
Now the amp is making a screeching/wailing noise and sounds like it's possessed by demons. Probably from too much rooting around inside.
Might be a good time to start over.
Mostly I'm wondering if there is a good way to run the input and volume wires 6 inches or so from the chassis without creating noise.

[Mick Bailey]

The amp worked fine when everything was mounted in the chassis. I would find out what's wrong rather than starting it again, otherwise you won't learn anything from fixing the fault. Plus, you risk doing all that work to find yourself back in the same situation.

1. The hum is possibly a ground loop hum from the grounding scheme. Attaching a ground to the chassis is fine, but the location of chassis grounds is critical - are you grounding to the same points as you did originally?
2. If it isn't a ground loop hum, it may be induced hum in the pot or socket. The pot shell is grounded when it's located on the chassis, but if you move it out on a screened lead you may need to ground the shell of the pot. Similarly, the socket may need to go inside a screening can. Consider mounting both of these in a cheap sheet metal enclosure behind your panel. I've even used cardboard covered with screening foil for this, so long as there's continuity. Some commercial equipment uses a similar material.
3. Try chopsticking the wiring to find out if you have a bad joint that's causing the screeching. You could have a bad joint that just needs re-working.

[bsco]

interesting as I have a bunch of old tube radios and I am thinking of taking one of them and converting it into a guitar amp and try it for recording purposes......just to see how it sounds.......I think it would be a very interesting project to do.....maybe I could still keep the tuner section intact so it could still be used as it was previously intended...

[Helmholtz]

Mostly I'm wondering if there is a good way to run the input and volume wires 6 inches or so from the chassis without creating noise.

Running a shielded 6 inch wire to the input jack shouldn't be a problem at all. That's just a short extension of the guitar cable.

A problem might be the proximity of input and vol pot wiring.

Do you have the 100k to ground like the original amp?

It would really help to see a drawing of your wiring showing every single wire and shield. Your pic is not really helpful.