Fixing the Reverb Tank

The reverb tank is definitely a weak spot, but its most common problem is fixable if you have the time and patience.

Check the continuity at the tank itself by measuring the resistance at each RCA jack (plug in a jumper cable for ease of access). The input side (towards the center, where the red wire goes) should measure around 60 ohms. The output side (black wire, on the right, looking at the back of the amp) should measure around 200 ohms.

It’s not uncommon for the wires that go from the input and output jacks to the reverb transducers to break right where they go into the white plastic push-on connectors. The green and black wires are pressed into the back of the push-on connector, and the connector has an insulation-piercing blade that slices through the insulation and makes contact with the wire. Unfortunately, the blade sometimes nicks the wire and it breaks right there.

Track down the broken wire by looking for continuity with a ohmmeter on each wire, from the pins to the jack. When you find the bad one, pull the wire out of the push-on connector with long-nose pliers, trim the broken portion, and push it back in again with a thin screwdriver so the blade re-pierces the insulation.

If that doesn’t do it, the problem may be with the tank itself. The very fine wires from the transducer coil to the push-on pins may have broken. You should have continuity through the pins–If you don’t have continuity on both sides of the tank, one of the fine wires is broken. These are very hard to resolder–I have to work under a magnifying lamp to do it.

At this point, you may want to just replace the tank. They’re less than $25 from suppliers such as Antique Electronics and Mojo Musical Supply. The stock replacement tank is the Accutronics 8EB2C1B. If you like long, surfy reverb and darker reverb tone, the Belton and MOD tanks available from Antique Electronics(www.tubesandmore.com) are functionally similar to the Ruby tank, which was just a relabeled Belton tank. I think the long-decay version, the 8EB3C1B, lasts too long, but that may be a matter of taste. The replacement tanks are all more sensitive than the stock Accutronics tank, so you may want to replace the reverb control with an audio taper (available from my Mod Kits page) to control it better. One combination you definitely don’t want is the long-delay tank with the stock reverb pot. It’s barely usable on 1 or 2.

The longer tank, used in the Hot Rod Deluxe and Blues Deluxe, is electrically compatible with the Blues Junior, but it doesn’t fit inside the BJr cabinet. Some people have hacksawed the ends off the tank to make it fit, but the Ruby tank will probably give you all the reverb you’d ever want.

reverbplugarrow

This is the back of the plug that connects the RCA jack to the reverb assembly. Sorry for the blurry picture, but you’ll see a pair of knives that cut the insulation when the black and green wires are pressed into the connector.

They often nick the wire, however, which breaks. Everything looks good, but there’s no connection or it only works occasionally. The fix is to pull the wire out (find out which one with an ohmmeter), trim the broken part, and reinsert it. Push it in with a jeweler’s screwdriver or other small blade. You can also eliminate the white plug entirely and solder the green and black wires directly to the pins on the reverb unit.

Reverb IC failure
Rarely, the reverb integrated circuit can fail. It’s a very inexpensive dual op amp (operational amplifier). In the green board it’s a TL072, in the cream board it’s a 4560. They’re completely interchangeable. In the little 8-pin package there are two amplifiers, one for sending the guitar signal to the tank, the other for recovering the reverb signal from the tank.

It’s very easy to test the recovery side. Turn the amp on. Set the reverb and master volume to 4 or so. (If you have a stock green board, the master volume won’t matter.) Pull the black wire from the tank and touch the center pin of the RCA connector (there is no danger of shock). You should hear a buzz that gets louder and softer with the reverb control. If you don’t hear the buzz, the connector, wire or chip is bad.

It’s a little more difficult to test the send side, but if you connect a small speaker to the red RCA connector, you should hear your guitar through it. Turn down the master volume so you can hear it. The speaker impedance is wrong for the op amp, so don’t keep it connected for long–just enough to verify that you have a signal going to the tank.

When the reverb IC fails internally, it sometimes pulls down the supply voltages. Check the voltage on pins 4 and 5, which should be -15VDC and +15VDC respectively. If one reads low, perhaps 9 or 10 volts, the chip is likely defective.

If you decide to replace the chip, the traces going to it are thin and closely spaced. Cut the leads off the chip, close to the board, on the component side. Then desolder the stubs, using a vacuum spring plunger type solder sucker to remove the solder and the stubs. Install a low profile machined socket instead of soldering in another chip. If the second one fails, the board probably wouldn’t survive another desoldering. Machined sockets are made far better than the simple spring type, and low profile sockets prevent oscillation.

137 Comments

  1. 1fastbullet says:

    I have a cream board, mim BJr that had a reverb problem I recently fixed.
    As Bill has pointed out, the problem was the little 24ga wire(s) in the tank not carrying a signal to the reverb springs.
    The thing is, it appears that Acoustisonic has made an effort to remedy the issue (and failed) as the connectors in the tank of my reverb are not the same as those in the photos Bill has posted. The connectors in my reverb tank are the equivelent of the ones Dell computers use to connect its fan(s) to the motherboard.
    It happened that I had one of these connectors laying around and was able to de/re-solder the connector and wires to the RCA connector on the tank.

    But there is something else I wanted to mention and inquire about:
    After I repaired the wire connections & installed the tank back into the computer, I happened to notice that the tank, itself, was magnetically attracting my screw driver. Yes, the speaker magnet was also trying to take the driver out of my hand, but I was amazed that the reverb tank had such a powerful magnetic force. It was also obvious that this magnetism was reduced the farther my screw driver was moved toward the right-hand end of the reverb tank. Obviously, this magnetism was resulting from the tank’s close proximity to the speaker magnet. (I should note that the speaker is not the original- It is a Warehouse [WGS]) with the magnet situated only an inch and a quarter above the corner of the tank.

    I have three questions, then:
    1) Is it feasible that the magnetic effect is damping the reverb (which I am acceptibly happy with)?
    2) Would a reverb bag reduce or eliminate the effect?
    3) What real purpose does a reverb bag serve?

    Thanks in advance.
    Mark

    • bill says:

      The tank shell becomes magnetic because of the field from the speaker magnet. The shell prevents most of the large magnetic field from the speaker from affecting the springs in the tank. A reverb bag has no effect on the magnetic field. Its job is to reduce mechanical feedback and vibration from the cab to the tank. Some people hear a big difference between bag/no bag. I mostly don’t hear it.

  2. Tridyed says:

    Bill, I want to get a different reverb sound that has a warmer darker tone. I do not want to use a pedal reverb but the stock fender one seems to be very pingy and I would like to get a warmer tank for my Blues Jr, any suggestion ?

    Thanks (watching for the delivery truck this week for my mod kits to show up)

    8)

  3. Tomshayes says:

    Hi Bill

    I have had no reverb since almost day 1 of owning my Cream board.. I carried out the continuity checks to the tank itself by measuring the resistance at each RCA jack. The input side measured around 60 ohms. The output side measure was off the scale.

    So I fitted a new Belton tank, but alas still no reverb.. I did the tank checks and the readings were fine. i.e. 60 and 200..

    I tested recovery side and not a sound no buzz etc..

    I checked continuity and the RCA jack cables are OK up to the board.. Do you think the BA4560 could be at fault?

    Regards

    Tom (UK)

    • bill says:

      Check the bottom lead of D7. I’ll bet you have no +15V. You can replace it with a 15V zener diode if so. You could also have no -15V, but then your Fat switch wouldn’t work.

      The op amp can fail too. When it does, it often pulls down one of the +/- 15V lines to around 9V.

  4. Tomshayes says:

    Hi Bill.

    I changed the I.C. and still no reverb??

    I fitted a TL072 as per your instructions>>>>

    I am now at a loss..

    Tom (UK)

  5. Tomshayes says:

    Hi Bill

    Due to time difference I changed the op before I read your latest comment.

    Do you suggest I still try the D7 test?

    Tom (UK)

  6. Tomshayes says:

    Still fails the buzz test..

    Now do I check the voltages between chassis and either side of the diode?

    If so with the meter set at 20v DC I get 0v topside and -0.72 bottom side!

    Thanks

    Tom (UK)

  7. Tomshayes says:

    Hi Bill

    Still no joy I’m afraid.. I have swapped the diode for a fresh one but it’s made absolutely no difference..:o(

    I may have to put the amp in the bathroom to get some reverb!..

    Regards

    Tom(UK)

  8. Tomshayes says:

    Hi Bill

    I was going to make up a test rig as per your video but our electronics store does not carry 400v 0.01uf cap.. only lower or higher voltages.

    Any suggestions as to which way i can go with it?

    they have.50v, 250v, 275v 1250v or 2000v

    Thanks

    Tom (UK)

    • bill says:

      Higher voltage is always OK. Don’t go below the highest voltage you may encounter in the amp (350V). You can also use a smaller cap. Anything from .001 up to .01 will work. So .001, .002, .047….

  9. Tomshayes says:

    Hi Bill..

    Well I made the test rig and as far as I can tell I have a signal all the way through the reverb circuit from C17 through the reverb tank and all the way up to R16..

    I must be doing something wrong!..

    Still got no reverb!

    Tom

  10. Wes says:

    Bill,
    Thank you very much for your suggestions. Old tank in box; MOD tank in amp –> OMG. I have reverb now without the artifacts of a screaming child in a grocery store whose parents won’t come back for him. What a difference & much more of the breadth of the reverb control usable. Can’t wait to get the basic mods in there; I suspect it will only get even better from there.
    Took a couple of pics too as I swapped them & looked close – the Accutronics (as issued now with that amp) is seriously different geometry and a shame on Fender to put it in there. What a stark (but not in tone) difference for $18 or so for the MOD.

    Thanks again. Wow.

  11. deemika says:

    Bill,
    THANKS for the great info about fixing the reverb tank. My BJrIII reverb went out, and I saw your suggestions above. Sure enough, the two little black wires were broken at the connector. I followed your instructions, and I now have the reverb working again. I expected a better design from Fender; the reverb tank wiring is a HORRIBLY poor design.
    Muchas Gracias,
    Mike

    • bill says:

      Fender didn’t design the reverb tank; Accutronics did. Now they’re owned by Belton, which does a better job with connectors. But they’re still burning off a huge inventory of Accutronics parts. If you want a better 8EB2C1B tank, get the MOD or Belton versions. They’re more sensitive, so you’ll want to install an audio-taper reverb pot at the same time.

  12. bbqbrisket says:

    Bill,
    I was reading the info on reverbs and a little confused.
    I am interested in the more surfy sound (I guess as I am interested in surf music) but as I read it, the long delay from your perspective is no so desirable.
    Would the Ruby, (if I can locate one) be better than either the MOD or Belton or does the MOD just have a different part nbr.
    Help me clear it up.
    thanks
    Norm

    • bill says:

      Ruby just re-branded the Belton tank. I don’t think they do it anymore. You’re welcome to try the long-delay version, but I strongly recommend the audio-taper pot to help control it.

  13. bbqbrisket says:

    Ok….thanks Bill

  14. bbqbrisket says:

    Bill,
    I have a NOS 8EB2C10 (uninstalled for right now).
    note this has no letters at the end.
    Is this a fit for the BJ?

    • bill says:

      The last letter just indicates whether the mounting springs are set up for vertical, horizontal, or upside-down mounting. It never seems to matter in actual performance.

  15. Coen Bijpost says:

    Hi Bill,

    I’m having a very weird problem with my Blues Jr. As it’s a brand new amp that I modded after owning it for 2 weeks, I don’t know if I had something to do with it or not. Ok, here goes.

    Every once in a while (happened 4 times now) when I plug in my guitar with relatively high output humbuckers (I mostly play strats and teles), the reverb doesn’t work. Not every time, mind you. It’s never happened with the single coils yet. Don’t know if that matters (impedance differences or what not). When I switch the wires going to the tank (so they’re wired backwards) the reverb works! And if that’s not weird enough, when I switch them back, the reverb keeps working like it should. Also just taking them out and back in, or twisting the wires doesn’t work. So I don’t really suspect broken cables/inputs.

    I’ve no idea where to start looking, as it’s such a random issue, maybe you have some idea as to what it might be?

    Thanks in advance,

    Coen

  16. the_wagness says:

    Also having a weird problem with my reverb, often it doesnt work, BUT the remedy is to ‘bump’ or rock my amp just a bit, then I can here a familiar ‘crashinsg’ noise of the reverb, but cutting in and out, and sometimes it finally cuts back in and the reverb stays on for a bit.

    I know knocking my amp around probably isnt the best for its health, but is that indicative of a specific problem with the reverb?

    thank you for your time,
    -Erik

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