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Have a question regarding 12ax7's for you

I was playing my R6 through my Triwatt last night and got a phone call so I set the LP down and answered the phone.
While I was on the phone I heard what sounded like snow or ice falling down the roof, a sort of crystaline crunchy sound.

So I get back to the guitar and the volume is way down on the "linked" channel, try the other channels, "normal" is fine, have full volume, "bright" is dead

So, before panicking TOO bad (ZP, I know, rule 1 is DON"T PANIC , right up there with don't forget your towel), I switched in a different 12ax7 into V1 today.

All is now back to normal

Would I be correct in assuming that somehow I lost a triode in my NOS Tungsram from the Sarge Only have about 10-15 hours on it at most

A non-functioning triode would take down the one channel it feeds (here the "bright" channel) and from the looks of the schematic I would guess that this would result in a volume loss on the "linked" input, correct

Should I pull the chassis and check for anything else

Thanks

Check that pins 4&5 are still connected to 6.3VAC. OTW you have one half dead tube. NOS sounds good and some actually last a while! It's always a gamble.

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Stephen
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I was using a NOS JAN Philips 12AX7 of mine in the prototype Triwatt's V1 position. After a while one of the channels developed an awful crackly "static" although it still worked. Turned out to be one of the triodes inside V1. I had used that particular tube quite a lot already so I couldn't really complain.

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Well I put about 40 minutes on my Triwatt with a replacement tube in V1 and it all sounds to be back to normal, "normal", "bright" and "linked" inputs all back to normal volume

I figured it might have been a triode failing in the 12ax7, but I've never had it happen before and wanted to get verification

Good news is I don't have to pull the chassis, bad news is I should figure out what I can make that only needs 1/2 of a 12ax7

Thanks for the help

How about a Hiwatt without the OD?

I've had som9e flaky things happen with tubes but that's a new one. My current personal favorite is several new issue TS 12AX7's that hum in every PP amp I own, but they work fine in my VJ & AC4TV. Go figure.

Hey Mr. C.
For giggles you should also try cleaning the tube pins. I've had all sorts of weirdness (especially with older tubes) that will clear up by taking a little Deoxit on a Q-tip and cleaning the tube pins. Also work the tube in and out of the socket with a little of the Deoxit on the pins to clean the socket. Residual flux left over from the soldering process can re-flow when an amp heats up and migrate into the business area of the tube sockets. Just working the tube in and out even dry can sometimes "enhance" the contact area.
BTW... You should never spray contact cleaner directly into a tube socket unless you have the amp apart and can then clean up the deoxit residue. I would prefer to see my techs spray the sockets from the inside out and mask off the outside somehow to keep that stuff from going everywhere!!

Hopefully the tube is ok. It's painful enough loosing a new production tube $$

Joe G

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