Does this sound like an amp/valve problem to you?

[_tom_]

ok, cheers. I ordered some new EI Elites but apparenty their factory is down for retooling so I couldnt get any in time for the weekend I was back :( I just dont want to spend £40 or so on a whole set of preamp valves only to find out theyre not the cause. I have a 5751 (70% the gain of a 12AX7) at home that I can give a go, should I just try it in each position and see what happens? Only thing is, because its a different valve and output, I dont really have a point of reference as I dont know what to expect, if you know what I mean. Its annoiyng living away from home, I cant get this all sorted easily :(

[hamfist]

I have a 5751 (70% the gain of a 12AX7) at home that I can give a go, should I just try it in each position and see what happens?

That would be perfect. There's no need to replace all the pre-amp valves. Just replace one at a time with the 5751.

 A 5751 is very similar to a 12AX7 really. All you might notice is a slight reduction in gain with the 5751 instead of a 12ax7.

However, if your problem is a faulty 12ax7 then when you do replace the faulty valve with your 5751, your amp's nasty symptom will disappear !

[Lazy_McDoesnothing]

I'd save up for a full set of tubes.  If they fix the problem, great!  If they don't, you have a backup set for when you need them next.

[_tom_]

Looks like the 5751 for V1 fixed it. I plugged in expecting dull mushiness but it was a lot tighter and clearer :) Played for about half an hour and it seems to have kept up the good sound for that, so I think its fine now. Hopefully it stays this way. The 5751 sounds really good btw, a lot brighter than the TAD stock V1 though.

[hamfist]

Looks like the 5751 for V1 fixed it. I plugged in expecting dull mushiness but it was a lot tighter and clearer :) Played for about half an hour and it seems to have kept up the good sound for that, so I think its fine now. Hopefully it stays this way. The 5751 sounds really good btw, a lot brighter than the TAD stock V1 though.

Glad to hear you improved things Tom.

Sounds like you might have had a bit of a duff V1 valve.  It would be interesting to swap a known good 12ax7 with your 5751 in V1.

BTW, a 5751 in the PI can be a really amp-tightening move with some 3-4 gain stage amps.

[d1dsj]

Glad it's sorted with the pre amp valve. FWIW... Another cause for this problem can be dirty/ oxidised jacks on the effects loop. I've had the volume fluctuations on a couple of amps over the years and at first I couldn't understand why it could be the case as I never used to use the loop. But a couple of times it turned out to be exactly that.... so keep the loop contacts nice and clean too whether you use them or not.

[jpfamps]

Parasitic oscillation can cause amps to seemingly randomly distort/ change volume, and can be a real problem in high gain amps. Reducing the gain can often solve the problem, and this might be why a 5751 seems to have "cured" the amp.

[_tom_]

For $%&#s sake, its back again :lol: The 5751 still sounds way better than the TAD 12AX7 in there, and the effect is less noticeable, but its still there every so often. Didnt start until about half an hour into playing today.

edit - d1dsj, I have the fx loop set to bypass so it couldnt be anything to do with that could it?