Smoking Ampeg R12R still powering on

[skycaptain]

Hey all,

I've had an ampeg R-12R (reverberocket) for a while, and it just recently went sour on me. Its been an amp in my studio for the last couple years, and spontaneously decided not to turn on one day. The fuse was fine, so I though one of the power tubes was bad. It had EL-34s in it, and one of them looked a little fried. I didn't have any spare el-34s, but I had a pair of 6L6s. I have a second reverberocket with 6L6s in it, so i figured my other r-12r could also take 6l6s. I swapped the 6L6s with the El-34s, and the amp powered on, but with a big flash and a little smoke. the spark occured on the ther side of the circuit board, I couldn't see what was sparking. I immediately turned the amp off to inspect it, and the fuse was fine. I turned it on again, and the same thing happened, it powered on with a bright flash, smoke, and I turned it off in a split second. I put the bad EL34s in again, and it powered on again, but with the same smoke and same flash. The El34s previously would not power the amp on, so i'm a bit confused.

I know the 6l6 tubes were fine because i tried them in my other amp with no problems. The only other strange symptom that the bad amp showed before it stopped turning on was a strange laser beam like sound it would make every 20 minutes or so. It literally sounded like a laser sound from a 60s star trek show. I'm defintely going to take it to a tech, just would love to know if this has happened to anyone and if they did anything to prevent it in the future, or did anything to fix it. thanks!

[Justin Thomas]

Schematic, please? Is this a vintage Reverberocket? Or a "reissue?" R12R, R12R-B, R12R-T, GS12-R, R212R? I'm aware of no vintage Reverberocket of any year that took EL34s, and if it DID, I <HOPE> the PT was changed or a filament tranny added...

The only time I ever had an amp make a laser beam sound was when a power tube lost its vacuum once. I don't recall the specifics, but there are differences in how the sockets are wired between 6L6 & EL34. They also require different bias setups, but I would think that wouldn't cause INSTANT problems...

Justin

[skycaptain]

schematic: http://www.thetubestore.com/lib/thet...-Schematic.pdf

Its a R-12R (reissue). When I bought it used years ago, it was set up with 12ax7's and EL-34's inside, and worked well for years. After you say most of them come with 6l6s I'm assuing someone set up the amp for EL-34s after the fact before it got to me. It recently had a short (about a year and a half ago), but i got that repaired, and the tubes were also replaced then with fresh 12ax7's and EL-34's. I don't recall if the tech replaced all the tubes, or just the bad ones.