fixing a reverb tank

[RSRD]

can someone guide me through fixing the reverb tank in my marshall jcm 900? I have no response from the reverb knobs on either channel. Is there any common ailments in reverb tanks or something i should look for?

thanks for any help

[VaughnC]

Obviously, if there are reverb drive and recovery tubes, check those or replace them first. If the drive & recovery amps are solid state, you could have a bad opamp, etc..

The next step would be to make sure the cables to/from the tank are good and properly seated in their respective sockets.

If the reverb tubes & cables are good, due to their construction, reverb tanks are subject to vibration damage. A common tank failure is caused by breakage of the small wires (inside the tank) that connect from the in & out jacks to their respective transducers. From vibration, the wires usually break right where they connect to the jack....so all you really need to do is strip the insulation on the broken wire back about 1/8" and resolder it to the appropriate jack connection. However, sometimes the wire(s) will break at the input to the transducer itself....which usually makes it's not worth repairing.

Note: if you have and know how to operate an ohm meter, you can tell pretty quickly if you have continuity through the in & out transducers without actually removing the tank from the amp. Just unplug the tank wires from the amp end (but remember which one went to which socket) and measure the resistance from the center pin to the shell of each plug. One plug should read fairly low at around 8 ohms or so and the other should read in the neighborhood of 100-1000 ohms or so. If either plug reads open circuit, chances are one or more of the tanks internal wires has broken, a transducer has opened, or the cable itself is bad or not making good contact with the tank socket.

[Fuchsaudio]

You can take an audio cable from either the input or output of the reverb pan to any quitar amp, and check that the transducers are good. Rocking the tank (or jiggling the springs) should make that noise we all know. A replacement pan should be 20 to 30 bucks retail, and is the most common reverb failure.

[John Phillips]

The most common failure of the lot is simply a broken wire inside the tank - usually where it joins the tag on the phono connector. It's very easy to fix if this has happened - just strip off about 1/16" of insulation from the wire (be very careful not to pull hard on it or you may rip it out of the transducer winding) and resolder it to the tag.

They tend to break here because the wire gets flexed every single time the central suspension is shaken (which is all the time), and the soldered joint is less flexible and more brittle than anywhere else. It is possible, but much less likely, that it has broken at the winding, which is a much trickier fix.

I've long since lost count of the number of reverb tanks I've fixed like this - it's by far the most common fault, much more so than drive/recovery tube failure (which you haven't got since the 900 series uses solid-state ICs for this) or failure of the main connector cables - which does happen too, especially on Fenders, at the amp end where they get knocked.

[RSRD]

thanks for all the help. I pulled out the tank and the wires seemed to be connected. we ran it thru another head and got nothing. when we ran his tank thru my head it worked. my tank does make the shake and shimmy that all reverb tanks make. so i am not any further along in finding a problem. i suppose i will have to cough up some $$$ and replace it. Any recommendations on a new tank? maybe that needs to be a new post!

thanks again for all the insight. wish i was smart enough to take a more in depth look.

thomas

www.runsilentrundeep.com

[John Phillips]

If another reverb tank worked in your amp you do at least know that it's definitely the tank.

If the wires look connected you're as well just replacing it probably - either the drive coil is blown (not the return if it makes a noise when shaken) or there's a break in the fine wire or solder connection at the coil. I just repaired one exactly like that today, but it was a real pain - it would have been cheaper in hourly rate to just replace the tank probably, but I didn't have a spare one to hand and I did have the time, so I fixed it. Not recommended if you're not experienced at these things.

I'm not certain of the right spec for a JCM900 - it's a solid-state-driven reverb, so it may well be different from the usual tube-type ones. Simplest is probably just to call a Marshall service agent and see if they will get you one.

[dazj]

I have a 65 twin and my tank got broken by customs GRRR!!! I managed to get a 66 replacement. One of the two springs had broken away from the transducer (the bullet shaped bit (4 off in total)) - both ends. I have all the bits, but I can't see that it can be repaired ... can the end cap be desoldered, removed and the tiny copper cabled spring holders replaced? There are 2 tiny rubber sleeves on the wires just beofre the hooks that hold the spring. The coils are fine.

The replacement I got to work .. it had a broken wire and a missing RCA socket. So I swapped the stamped chasis over. I looked around for a replacement though and found quite a few in the US - new ones. One guy was particually helpful and offered 2 or 3 spring replacements - for longer reverbs, though I'd suggest not with your Marshall.

I had a problem with a friends origonal 74 red Artiste combo. That was just wiring too. let me know if you'd like a few suppliers of tanks / pans.

Happy new year one and all!

[davidp158]

John,

I've been reading about broken reverb tanks, and your suggestion to look at the tiny wires. They appear fine, so I suspect mine has a defective transducer/coil. The output side seems to work, as I hear some reverb when I tap on the pan. Can you advise me on how to attempt fixing the input side coil? I can always buy a replacement pan, but figured I have nothing to loose by trying to fix the one I have.

BTW, I temporarily put another reverb pan in the amp, to confirm that the stock pan was dead. Is there any risk of damaging anything by using an "out of spec" pan. I didn't write down the model number of the pan that's in there now, but its a short Accutronics pan. The original (defective) pan designation is "9EB2C1B", which per the Accutronics codes translates as:

9: type 9 model
E: input impedance = 800 ohm
B: output impedance = 2575 ohm
2: medium decay time (1.75 to 3 seconds)
C: input insulated/output insulated connectors
1: no locking devices
B: horizontal, open side down

regards,
Dave

Originally Posted by John Phillips

If another reverb tank worked in your amp you do at least know that it's definitely the tank.

If the wires look connected you're as well just replacing it probably - either the drive coil is blown (not the return if it makes a noise when shaken) or there's a break in the fine wire or solder connection at the coil. I just repaired one exactly like that today, but it was a real pain - it would have been cheaper in hourly rate to just replace the tank probably, but I didn't have a spare one to hand and I did have the time, so I fixed it. Not recommended if you're not experienced at these things.

I'm not certain of the right spec for a JCM900 - it's a solid-state-driven reverb, so it may well be different from the usual tube-type ones. Simplest is probably just to call a Marshall service agent and see if they will get you one.

[wjd]

Hi guys. i know its an old thread but thanks for the info.
im putting a new tank in my vs102r, but ive gone and forgotten which connections are which...
im pretty sure the red RCA is for the output of the tank, but could someone please confirm this for me?
cheers

[WaltC]

it's not a big deal, try them both ways, the wrong way won't work and the right way will (if there are no other problems of course <G>).

[RSRD]

Wow, you revived my thread I started 8 years ago!!! Long live the Gear Page!

[jjudevine]

I am just getting back to the the repair world, and am repairing a Silvertone 1484 twin.
I have a reverb tank that the transducers are broken and a rusted single spring.
Does anyone know what a good replacement tank would be? All I have for numbers is a (CS55), a Sears part number.