Question about current production reverb tanks

[Esquirefreak]

Hey, everyone!

I recently did some maintenance on a '66 Super Reverb AB763 and haven't gotten around to plug it in until today. My left arm went numb 3 weeks ago from a suspected nerval injury, so playing guitar is kind of a struggle 

Anyhow;
I have a pretty bad hum from the reverb. The hum intensity increases as I dial the R pot up. My guess was a noisy recovery stage at first. However, disconnecting the pan kills the hum completely.

One of the springs in the original tank had come loose and I bought a new tank. It just now struck me, that the new Accutronics tanks RCA jacks are isolated from the pan itself. So the pan can't see no ground, right?

Well, my question is simply - Should the tank be grounded? And if so, should it be grounded at both ends or just one of them?

Greetings from Sweden.
/Max

[PRR]

Dumb answer: get a few clip-leads, ground here or there. Either it will stop humming, or it will blow-up. And the reverb path is unlikely to blow-up.

Bonus dumb answer: brush the tank with your hand. (Brush in case it is shocking; unlikely but take care.) While also touching or NOT touching a grounded 1/4" plug. Probably the lowest hum is the best grounding on the tank.

[Esquirefreak]

Yeah, I just tested with a speaker cable, from the pan to amp chassis with no difference. I'll take the amp out of the cab and experiment further tomorrow. But I feel like since it's a strict hum, my guess is there is a loop or possibly a less than adequate ground somewhere.

And as for safety, I always use the one hand rule 

Thanks for replying!

/Max

[HotBluePlates]

... It just now struck me, that the new Accutronics tanks RCA jacks are isolated from the pan itself. So the pan can't see no ground, right? ...

Did you buy the correct tank?

The typical tank is 4AB3C1B, where the "C" means that the Input RCA jack is isolated from the tank's case, while the Output RCA jack has the Ground connected to the tank's case (and therefore the cable's shield, and the amplifier's chassis).

[Esquirefreak]

So, I rolled some tubes in the recovery stage socket. I have mostly RCAs, Telefunkens and Philips, Philips being my preferred tube most of the times. I had the reverb pan disconnected to hear the raw noise floor and found a nice quiet tube to use.

However, I had some static noises when turning up the vibrato ch. volume. So i rolled some tubes in v2 and found that ALL of them were picking up microphonics. I thought that was odd since I put all microphonic tubes in a separate box.

Hmm... I chopsticked around on the board and found a microphonic ceramic cap. Swapped that one. Kept chopping around and found that most of the board was microphonic. Okay? A lot of microphonics around the coupling caps.

Aha! This resistor looked suspicious...

I'm gonna keep experimenting with the ground hum of the reverb circuit.

[shooter]

and found that most of the board was microphonic.

If that's a Fender original fiber board might check it for continuity, they have been known to cause MANY "odd" issues.

[Esquirefreak]

Yupp, I've read about the boards becoming conductive. Major bummer if that's the case... I've yet to find out though, if it was microphonics or the 100Ω resistor making/braking contact when I was poking the board.

I'll get back to you when I'm back at my shop.

/Max

[Sonny ReVerb]

I know you've moved beyond the original question, but you can ground or isolate the tank jacks by adding or removing a solder bridge...

https://el34world.com/Forum/index.php?topic=23438.msg252180#msg252180

[Esquirefreak]

Well, it turns out that the reverb hum is induced by magnetic fields rather than a bad ground. With the tank and amp on the bench I quickly noticed a drastic difference when moving the tank closer/further away from the amp. Gonna try to shield it with some aluminum foil.

And also (from pulling the preamp tubes) I narrowed the microphonics down to one of the 6L6GCs. Swapping them around showed that the mechanic noise followed the tube. I have a couple of pairs that I will try in place.

/Max

[Willabe]

Well, it turns out that the reverb hum is induced by magnetic fields rather than a bad ground.

Do you have the verb tank oriented right?

Keep the verb tanks output end towards the input/preamp end of the amp chassis. That keeps it further away from the magnetic fields from the PT/choke/OT.

It's noise to signal ratio.

The verb tanks output signal is very low there. Lower than a guitars PUP output signal. The verb recovery gain stage amplifies both signals, verb tank's output and any stray noise signal. But the tanks output signal is too small to swamp any stray noise signal, so too much buzz.