Reverb isolator replacement for Gibson Saturn amp

[700P]

Hi all,
Name is Rob, and I'm redoing a Gibson Saturn GA45RVT amp. It came to me in exceptional cosmetic condition, but with bad AC hum. I started by replacing all the electrolytic capacitors. After looking at the schematic & the 2 prong plug on the AC line cord, I quickly realized this was an electrocution hazard. Replaced the line cord, removed the "death" cap and rewired the polarized accessory socket so the hot was wired to the correct (smaller) prong.

When I removed the reverb from its vinyl sock, I found what I think was some sort of vibration isolator had turned to brown dust. What should I use to replace what was originally in the vinyl sock? Bubble pack? Foam peanuts? Soft packing foam?


Thanks for looking,
Rob

[Tom Phillips]

...I found what I think was some sort of vibration isolator had turned to brown dust. What should I use to replace what was originally in the vinyl sock? Bubble pack? Foam peanuts? Soft packing foam? ...

Welcome to the Forum Rob.

It is common to find soft rubber grommets in the four large holes of the reverb unit's metal case. I'm thinking that's what you found. They can be replaced with common rubber grommets as used to protect wiring passing through holes in sheet metal chassis. You don't want to put anything loose inside the isolation bag that holds the reverb spring unit. If the material were to move around and come into contact with the springs it would interfere with the reverb function and would produce extraneous noises. There is usually a cardboard cover over the bottom of the pan mounted with spacers to keep it from contacting the springs. Please take photos of your unit and post them if you can.

[TomCarlos]

Like TP said, regular ole rubber grommets will do. It's getting hard to new find amps that use the isolation bag. So as mentioned, you can add some protection to the tank by using a cardboard protector. See pic.

The other Tom !

[olddawg]

I have had better results using a rectangle of 1/2" or 1" thick foam rubber and longer screws. It's less microphonic.

[Leo_Gnardo]

You don't want to put anything loose inside the isolation bag that holds the reverb spring unit.

What Tom said. And adding standoff grommets to the base of a reverb tank in a bag, I'm afraid that will do nothing. Cardboard cover over the open side, yes, that's a good idea.

Now, how to mummify your reverb tank:

In extreme cases of feedback thru the tank evidenced by moaning or howling noises as the reverb is turned up, I've covered the tank's metal box with sticky-back foam. Get a roll of insulating foam intended to be used between a camper-cap and the rails of a pickup truck. I find the stuff at Home Despot, you may be able to find it at other spots. It's about 1 1/2 inch wide and 1/8 inch thick. Just put a layer of foam strips on every metal surface, for extra credit on the cardboard too. Now the foam covered tank will just about fit into its sock and you should find the howling racket much diminished or gone entirely.

[700P]

Welcome to the Forum Rob.

Please take photos of your unit and post them if you can.

Here's a few photos of the reverb and vinyl sock. No rubber grommets, just a thin piece of cardboard to cover the bottom of the reverb.

Rob

[700P]

Here's a peek inside the reverb. It's made by GIBBS Mfg & Research.

Rob

[olddawg]

If the tank has 4 mounting holes (and the picture looks like it does), just find 4 wood screws of the appropriate length. Put the bag over the tank. Put the screw thought the bag and the mounting holes and out the other side. Then put a 1" thick or whatever piece of foam cut to the right shap under it and screw the crews into the bottom of the cabinet. The tank will still be in its protective sock but isolated from microphonics by the foam. I've done this many times and some amps come from the factory this way. You could also use contact cement to stick the foam to the cabinet bottom, and the sock. I prefer to use black foam and black screws.

[Tom Phillips]

Rob,
Your reverb tank and bag look stock. However, I'm surprised that it has the four small foam pieces inside between the inner spring pan and the outer case. The original Gibbs design intended that the inner pan be suspended by the short springs. An improvement for the cardboard cover would be to space it aeay from the tank with 1/4" thick shims. That prevents the bottom cover from touching the springs if the springs sag or the cardboard warps. That's the way Fender does it.

Based on your photos I don't see what would have deteriorated and made the residue you originally reported. You didn't say that there was any malfunction and your parts are in good condition so you could just put the reverb tank back the way you found it for now. It will be easy to add mods later if necessary.

Tom

[Jazz P Bass]

Didn't some of those older reverb bags have a foam layer on the inside?

[g1]

Rob,
Your reverb tank and bag look stock. However, I'm surprised that it has the four small foam pieces inside between the inner spring pan and the outer case. The original Gibbs design intended that the inner pan be suspended by the short springs.

Agree with Tom that these foam pieces are odd. I don't think they should be there. Perhaps someone found the same foam you found and added these pieces thinking that was what may have been there?
Or maybe the original manufacturer shipped the tanks to Gibson with this foam for transport and someone on the line forgot to remove the pieces? Some new tanks do ship like this to avoid damage and the foam is supposed to be removed before installation.

[Tom Phillips]

Didn't some of those older reverb bags have a foam layer on the inside?

Not sure about that but some old bags were made with thicker material and Fender even doubled up to two layers. Overall the old bags were more substantial than the modern replacements.