noisy reverb in ab763 super reverb

[galtjunk]

I have a Drip Edge 1967 Super Reverb.
It has been recapped.
It sounds great until I turn on the reverb.
I have replaced the preamp tubes.
It is on my amp stand so the reverb cables won't reach.
I have jumpered the reverb in and out jacks on the chassis with an rca cable.
I am plugged into the reverb channel.
It is quiet with the reverb and trem controls on 0.
With all controls on 0 it gets really noisy when I turn the reverb control up.
Bacon frying.
It goes silent when I plug a jumpered rca into the reverb switch or turn the reverb down.

Any ideas?

[pdf64]

‘Bacon frying’ is typically due to the anode load resistor of the affected stage (ie V4 pin1). Note that it may measure within tolerance yet still generate the sizzle.
But if that was the case, it may be strange for the reverb shorting plug to kill it (ie connecting V4 pin2 to 0V chassis common). Dunno.
I suggest to try replacing the V4 pin1 100k anode load resistor and see if that sorts it.

[galtjunk]

I replaced the 470 and 1k5 on each 6l6 socket.
I replaced the 100k on v4 pin 1.
The noise has cleared up.
Now the reverb pot acts like an attenuator. It adds reverb but cuts the volume.
At 10 I get deep reverb but very little volume with the volume and tone controls on 5
As I turn down the reverb the volume goes back up to normal.

[pdf64]

I replaced the 470 and 1k5 on each 6l6 socket.
I replaced the 100k on v4 pin 1.
…

So that was all you did, eg nothing else changed?

How about if the reverb is set to minimum / 1 / full CCW; can the dry signal still be heard?

[galtjunk]

Reverb at zero give full volume with no reverb.
At 4 the reverb starts and the volume decreases.
There is a slight bit of hiss until 4 then it quits and a slight high pitched sound and a slight hum starts.
The volume drops steadily as reverb increases.
I did change v2 because it was a little microphonic but it didn't change the behavior of the reverb control.
V2 is still a little microphonic but it is better than the previous tube.

[mojotom]

I had an issue with that one SF amp a few months ago and got a high pitched noise when adding Reverb, spend a lot of time trying to find the issue and it was the footswitch that was not properly connected, trem on reverb and reverb on trem and by doing so it create an antenna for the signal path.
From what I read here your footswitch is not even plugged, is it ?

[galtjunk]

It is plugged in now.
I also reconnected the reverb pan.
I unplugged the pedal and everything is working properly now.
It is a non Fender replacement pedal.
Everything works with a shorted rca plug in the Tremolo jack and nothing in the reverb pedal jack.
There is motorboating in the tremolo when the speed is set to 10 but it quits if you turn it down to 9.
I'll see if I can fix the footswitch.
If not I can live with it this way.

Thank you all.

[pdf64]

Has V4’s cathode bypass cap been replaced?

[galtjunk]

All electrolytics have been replaced.

[mojotom]

It is plugged in now.
I also reconnected the reverb pan.
I unplugged the pedal and everything is working properly now.
It is a non Fender replacement pedal.
Everything works with a shorted rca plug in the Tremolo jack and nothing in the reverb pedal jack.
There is motorboating in the tremolo when the speed is set to 10 but it quits if you turn it down to 9.
I'll see if I can fix the footswitch.
If not I can live with it this way.

Thank you all.

Maybe try to switch the two RCA of the footswitch, you may have the trem switch connected to the Reverb switch.

[sluckey]

I unplugged the pedal and everything is working properly now.
It is a non Fender replacement pedal.

The AB763 amps require a shielded cable for the reverb F/S. Most non Fender pedals are not shielded.

[Roe]

try:
- split cathode on v4
- replacing the 3m3 with a metal film resistor
- shielded reverb cables
- insulated rca phono plugs

drastically cutting noise would require quite a bit of rebuild though

[martin manning]

I unplugged the pedal and everything is working properly now.
It is a non Fender replacement pedal.

The AB763 amps require a shielded cable for the reverb F/S. Most non Fender pedals are not shielded.

I recently bought an aftermarket two-button foot switch for a DR. One of the two conductors is shielded, but the switches were miss-identified by the label. Removing and replacing the sticker correctly solved that.

[galtjunk]

I'll see what I can do with the footswitch.
The reverb is quiet if I don't use the footswitch.

[sluckey]

I'll see what I can do with the footswitch.
The reverb is quiet if I don't use the footswitch.

If the reverb cable to the FS is not shielded, you need to replace the cable. This is what the Fender cable looks like...