Reverb won't work on my Twin

[Budreax]

I have a silver face twin. It's got the Master Volume with the pull knob.
It recently started acting funny. It had the tubes that were in it when I bought it, so I replace the quartet of ruby 6l6gc's with GT 6l6 ge. I didn't rebias because it was 6l6 to 6l6, and everything seemed okay. A couple days later the reverb just quit. Nothing.

I took it home and plugged in the foot switch and I can here the buzz change when the reverb goes on and off, but that's it. I have taken the spring out and unplugged and replugged all the in's and out's, still nothing.

This amp has been my work horse for several years and (aside from it's weight) it's never let me down. The tone is still pretty good but I love the reverb and use it a lot, besides it seems pretty silly to have a twin with no reverb.

[mac1amps]

First off, just because you didn't change to a different model power tube doesn't mean you don't need to re-bias. When changing same type tubes of the same manufacturer, you're most "apt" to be pretty close, whereas changing from Rubys' to GT's (the GT's are NOT LIKELY to be Rubys'.....but they could be almost anything else........in case you weren't aware, GT doesn't manufacture their own tubes [at least not yet]).....it's highly likely that they will bias differently.......with respect to your reverb, the most common problem is the spring tray going bad. SOMEtimes a small lead comming from one of the transducers to the RCA jack will break at the jack end, and it can be easily resoldered. Other times, the wire MAY break at the transducer, in which case you'll have to replace the entire tray (in "the old days" you used to be able to get/install replacement transducers for the spring tray, but it wasn't "cost effective")......Yah, it's also possible that the drive tube/transformer may have failed, but that doesn't happen anywhere near as often. Then again, it may just be a bad connection in the cords to & from the tray...........If you really DO love your Twin.....maybe you should take it to an experienced tech........(just a thought)

[52 Bill]

On your amp, a bias adjustment will require the changing of a resistor, as the original circuit has a bias balance control.

As mac sez, in order for the amp to work at an optimum level the amp should be rebiased any time the output tubes are changed. If the new tubes are working and sound fine with no signs of red plating (overheating), then it should work fine for you.

In my experience, 95% of all reverb problems are tank related. If you've already checked the cables and connections, remove the tank from the bag in the bottom of the amp. Remove the cardboard bottom cover and carefully inspect the two long springs and the small wires that attach the transducers (coils) to the RCA jacks.

If the springs have broken loose, then you will have to replace the tank. If one or more of the small wires located at either end of the tank has broken, they can be repaired, and the tank will in most cases work just fine.

If you have an ohmmeter, you can test the tank wiring without removing the tank from the amp by reading the resistance across the RCA plugs that plug into the back of the amp. If you read the resistance on the wire that plugs into the right jack, you should see about 1-2 ohms. The wire that plugs into the left jack should read around 180 ohms.

Let us know what you find.

[Budreax]

Trying this out

Hello,

I will go and try to use my OHMS meter on the reverb. I will also try to take the spring-tray apart. If I find som loose wires I will try to re-connect them.

If that doesn't work I am close to Chicago, and playing there soon, know anyone good Mac?

Later
Budreax

[Budreax]

Tried the OHMS meter.

I tried the ohms meter, at several differnt settings. I consistently hit 1 or there about from where it started on the right plug.

The left plug was much more inconsistent. Sometime this week-end i will look inside the tank to check for broken connections.

I do really like this amp alot. I would take to a reliable tech right now if I knew there was one near-by.

later
budreax

[Amp Kat]

Be careful with those green and white wires on the little transformers on that rod as they are very britle and if they break off that pan is pretty much toast. Good to have a spare pan for quick connect testing and I realize not the case here but I do agree with Bill that most problems are either pan or connection related. Once in a blue moon a bad tranny and it is possible that 1/2 of the 12AT7 driver tube is bad so you may try swapping that too.

[Budreax]

Fixed for now

Thanks YO!

I took apart the tray and a green wire had come loose inside just on the other side of where the rca pluggs in. Shave a little plastic drop a little solder, and it seems reverb is working again. Those wires are tiny.

I put the old tubes that were in it back. I figured a least they "SHOULD" be biased correctly, but who knows? Used amps. I got a couple phone #'s for local techs. I will use the "new" GT's as back up. In the meantime, I have started using my Bassman again and that is going pretty well also.

Later
Thanks again for the help.