73 Super Reverb

[Doc Stitches]

73 Super Reverb....finally got it working....thanks Bill52 and others .........( someone

had the neutral and hot wires reversed at the AC receptacle ) I am

innocent....of course !

Normal channel is great, but channel 2 has low volume, ( like it is on 1 or less ) even

on 10. All tubes test good. Channel 2 Treble and Bass knobs are not working either.

Reverb is working.

Doc

[Jazz P Bass]

May I suggest that you measure Ch 2 preamp tubes at pin 1 & 3 / Pin 6 & 8.
Post the results.
Go from there.

[Doc Stitches]

V4 236 2 63 2

v5 372 0 366 0

v6 240 92 214 92

[Jazz P Bass]

Vibrato Channel tube # V2 is the input tube for that channel.
It seems to be missing.
V5 is not doing anything.
V4 & V6 look good.

[Doc Stitches]

V2 221 2 199 2

Thanks for the aa763 schematic.

Doc

[Jazz P Bass]

V2 static voltages look good.
You still must figure out why V5 is not conducting.

[pdf64]

'You still must figure out why V5 is not conducting.'
V5 is the trem oscillator, if the footswitch isn't in and on then it won't be doing much; don't really need to worry about it at the moment?

'V4 236 2 63 2'

Pin 6 looks too low but the cathode voltage is holding up - could you confirm those?

'v6 240 92 214 92 '

Probably not relevent to the present issue, but it might be worth checking the plate resistors.

'V2 221 2 199 2'

OK but again the plate resistor values look like they may have drifted.
Once the root cause has been identified, consider a campaign change out of all plate resistors.
Pete.

[Doc Stitches]

confirm......V4 pin 6 65v

I'll check the PL resistors now

[Doc Stitches]

I shorted the vibrato pedal RCA jack and now I have pin 3 at 3v and pin 8 at 6v and Pin 1 at 480 and pin 6 at 405

[Jazz P Bass]

Channel 2 Treble and Bass knobs are not working either.
Doc

Run a continuity test on the treble & bass controls.
Short of that, you can bypass the tone circuit with a temporary jumper wire.
If the amp livens up, you have localized the problem to the tone circuit.

[Doc Stitches]

Bass and treble controls .... good continuity.

How do I bypass the tone circuit........where does each end of the jumper wire connect ?

[pdf64]

I would tack a capacitor (around 0.01uf) between the hot end of the volume control and the plate of the 1st stage, eg the plate side of the 250pF treble cap, and lift one of the 6k8 mid resistor legs (that goes to the chassis), whichever leg is easier. Pete.