Tweed cutting out

[audiosalvage]

Hi, I've just built a 5f2 amp, sounds good but at when diming either the vol or tone, it gets quiet and fuzzy. It's not gradual, it's a sudden change. Ideas?

[Stevem]

Here’s one thing to try.

plug in your guitar.
Turn its volume down.
Hook up a volt meter set for ac across the speaker .
Turn up the volume and tone to max.
Then look at your meter .
Do you see way more than a 800 milivolts ?
If so try this.
On the output tube swap the red and blue wires.
Does your sound still go low and get fuzzy?
If you amp then screams terrible put the wires back the way you had them.

[audiosalvage]

Definitely not that, my dog let me know

[Stevem]

You may have a bad coupling cap.
Caps also have a max ac ( signal level ) rating besides their DC rating .

Most time it’s safe to assume that half there DC rating is what there max ac is.

Try jumping out V1b and go right from the out of the volume pot to the input cap on pin 5 of the output tube.

What changes then take place?
Lower audio output, but clean?

[audiosalvage]

Jumping from vol out to cap just before pin 5 yields quieter sound. Pots are scratchy though. These are all new components

[audiosalvage]

I did notice on older schematics there is a 100k resistor before the vol pot. I put one in and helped a lot, but now I get low oscillation on tone pot when turned down

[lonote]

Pots are scratchy though. These are all new components

DC on the pots?

Leaky coupling cap from V1a to the tone control?

[audiosalvage]

I moved the amp to my practice room and it almost sounds normal. I think I have some bad juju with my shop power situation. Further testing after the holiday. Have a happy one.

[audiosalvage]

All new caps

[lonote]

All new caps

Right.. but new does not necessarily mean good.

Likely OK, but a lesson learned long ago.

DC on the pots?

[audiosalvage]

I meant I changed out the caps and added the 100k to v1b pin 7 and all is quiet. I also changed the cathode bypass cap from 25uf to .69uf.

[johnnyreece]

Right.. but new does not necessarily mean good.

I have an auto mechanic buddy who said "NEW" stood for Never Even Worked. Good thing to keep in the back of your mind (even if it doesn't necessarily apply in this situation).

[lonote]

Working on cars was my first lesson in that principle...