Amp repair where do I start

[Helmholtz]

A 1000Hz signal contains no bass, so the bass control has no effect.
You should see an effect with a 100Hz signal.

[LoveChet]

Ok on Bass I see. Accordingbto my 32 channel EQ, Bass is 20 to 200, low mids are 250 to 500, mid mids are 630 to 1k, high mids are 1.2k to 2k, and treble is above 2k

[LoveChet]

To get Chet Atkins tone with the EQ in the fx loop I lower the low mids, gradually peak the mid mids, and the lower the high mids.

[LoveChet]

On the upsteam side if the 250pf I get 150 mv or no gain. If I turn volume pot to max it drops it to half that. The bass and treble pots have no effect

[Helmholtz]

Cap looks bad. If you don't have a cap meter, best try a new one.

[LoveChet]

250 pf at what voltage rating ?

[LoveChet]

Is 250pf ceramic cap at 1000 v ok ? In the add it looks exactly what's installed now. Very small!

[Helmholtz]

At least 400V.

[LoveChet]

I increased the signal to 10,000 and exactly same result. Still no gain after that 250pf cap !

[LoveChet]

Do you think the bunch of different caps involved in the 6 position fat switch mod that follows the 250pf could have anything to do with the issue ?

[Helmholtz]

I increased the signal to 10,000 and exactly same result. Still no gain after that 250pf cap !

Did you change the cap?
BTW, are you using the probe's ground clip?

[LoveChet]

I just purchased a couple of 250pf caps from Mouser electronics. I remember that name from way back as being reputable. BTW, since the 250 pf cap is most likely defective that means that I never experienced what the 6 position fat switch was supposed to provide. I did notice that none of the 6 position made much of a difference.

[Helmholtz]

Ground clip connected?

[LoveChet]

Yup yup and yup !

[Helmholtz]

I increased the signal to 10,000 and exactly same result.

You can't mean 10000V.
Do you mean 10V at the plate?