Super reverb. Problem with the reverb

[blueserik]

Hi. When I turn up the reverb on my super reverb it starts to scream when it goes over 3 on the nob.
Is this due to a bad tube?

Thanks, Erik

[Firestorm]

More likely bad shielding on a cable. Check the cables to and from the reverb tank to make sure the shield isn't broken. It happens most often up near the back of the chassis. The footswitch (if you have one) is especially troublesome. One cable is shielded, one isn't. The shielded one is for the reverb, so make sure that's plugged into the right jack. And make sure the shielding is good on that cable, too. The footswitch is connected directly to the grid of the reverb recovery tube, so if there's a shielding problem, all kinds of noise gets injected right there.

[David Root]

I'm having the same problem with the mix pot in a redesigned amp's reverb. It has dwell, mix and tone like a 6G15.

It oscillates when I turn up the mix pot, and this is without the tank connected. The mix and tone controls are connected as in a tweed vol/tone control, I was wondering if I had some positive feedback in there somehow.

[tubeswell]

I'm having the same problem with the mix pot in a redesigned amp's reverb. It has dwell, mix and tone like a 6G15.

It oscillates when I turn up the mix pot, and this is without the tank connected. The mix and tone controls are connected as in a tweed vol/tone control, I was wondering if I had some positive feedback in there somehow.

possibly something to do with the layout/lead dress?? Or you can try sticking grid stoppers on some of the pre-amp grids. Maybe experiment with 10k-47k
2CW

[David Root]

All the preamp grids have gridstoppers except V4A which is the reverb tank recovery triode. Didn't want to put one on there but maybe I'll try a 10K. V4B is the second recovery after the mix/tone stack and has a 470K gridstopper.

The lead from the mix pot to the 470K is longish so I should probably replace it with the 24 ga co-ax I am using elswhere on longer preamp runs.

[blueserik]

Hi. Both cables are shielded and it doesn't look like a bad cable.
It has been on the same place for a very long time. One day it just didnt work as It should. One more thing that happens is when I turn up the reverb I loose all the bass.

Anyone?

[rfgordon]

The front-panel Fenders (Brownface, Blackface, Silverface) have very long grid wires that connect the tone caps on the board to the pots on the face. It's common for reverb signal to bleed into them, producing the odd and unpredictable parasitic oscillation.

If you move the tone caps/resistor from the board to the back of the pots and shorten the leads to the reverb pot, you'll take out almost 3 feet of unshielded grid wire from the amp.

It almost always cures odd problems in Fenders.

[Firestorm]

I'm having the same problem with the mix pot in a redesigned amp's reverb. It has dwell, mix and tone like a 6G15.

It oscillates when I turn up the mix pot, and this is without the tank connected. The mix and tone controls are connected as in a tweed vol/tone control, I was wondering if I had some positive feedback in there somehow.

Does it work with the tank connected? Do you have a grid to ground resistor on V4A? There is a design flaw in the 6G15 -- the lack of this resistor. When the tank is disconnected, the triode will go into runaway.

[Richie]

change the bypass caps for that section.. should fix it. common problem in fender amps..much different than a squealing tube..you can try a tube swap for the reverb,just to see if it is the tube first.. but i would be thinking its more the bypass caps. They will make the amp whistle or high end feedback noise when turned up. Bust you ears depending on how bad the cap is. Also may tend to make the amp sound thin and sterile.