Twin Reverb's Odd Reverb Problem

[RockNRollDr]

My 65 Reissue Twin Reverb was popping and cracking and I narrowed it down to a bad tube in V4. So I swapped it out and the amp now sounds great but now I don't have reverb and I'm pretty sure it was there prior to changing the tube. I reversed the RCA cables going into the amp and I have some reverb, like you normally would if the cables were swapped, but with them in correctly I have nothing. Maybe this isn't that odd but any help would be much appreciated, thanks.

[Leo_Gnardo]

It could be that popping and cracking was your V3 intermittently shorting on its way to going totally bad. Try a new 12AT7 there. If still no reverb, a failing V3 may have caused the primary winding of the reverb transformer to go open circuit like a fuse. Easy enough to put an ohmmeter on the transformer primary winding to check, if it reads infinite just replace that little transformer and you'll be back in business.

On rare occasion the reverb drive transformer develops an internal arc, that also could explain rackety noises.

What little reverb you hear probably results from acoustic energy from the speakers physically shaking the reverb springs.

[RockNRollDr]

I thought it could be the new tube in V4 so I tried 2 different known good ones and had the same problem. Also, with RCA cables in correctly I can bang on the tank and no noise at all, with them reversed I can hear it clanging when I bang on it. Thank you for the suggestions Leo.

[pdf64]

It could be all that popping and cracking was your V4 intermittently shorting, and that caused the primary winding of the reverb transformer to go open circuit like a fuse

I think you may have meant V3?

[Leo_Gnardo]

It could be all that popping and cracking was your V4 intermittently shorting, and that caused the primary winding of the reverb transformer to go open circuit like a fuse

I think you may have meant V3?

Whoa, correctamundo. My fault for giving advice before finishing first coffee of the day. Yes V3, 12AT7 reverb drive. Whoops! Look for edit coming up in just a minute . . . . put smiley face wearing a dunce cap here.

RockNRollDr please re read my earlier entry now edited. Thanx pdf64!

"Have you this misery a very long time?" yes, without coffee things don't go so well.

[RockNRollDr]

Thanks guys, I put a new 12AT7 in V3 and still the same issue. With cables in correct there is no reverb but with the cables swapped I get some reverb, I can't wrap my head around why this would happen. I will try to get it apart and test the reverb driver this afternoon to see if it is shot but I don't get why I would get some reverb with cables swapped.

[Stevem]

With a good ax7 in V4 and with the foot switch unplugged just in case there is a issue there you should hear the tank crash loud with the reverb up if you bounce the amp, if not the output side of the tank may be open which can be pinned down with a resistance check

[TimmyP1955]

Have you checked the tank? Disconnect it and put your Ohm meter across the RCA jacks. One side should read just a few ohms, the other a bit over 200. If there's no continuity, look for broken wires from the RCAs to the little transducers - it's a very common failure. (If it's a newer tank with molex connectors on the transducers, the connection can be bad even if the wire is still captive in the molex body. I've also seen dirty connections that were cured by unplugging the molex and putting it back. I've also seen the connectors stuck so badly that a pin pulled out of the transducer ;-(