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Ok, one of the tubes (EL34) on my Primaluna Prologue 1 appears to have burnt itself out. However, the amp still seems to play fine. My question - is it ok to continue using the amp while I seek a replacement tube? Sorry, brand new to tubes so haven't got a clue.

First, why do you think it burnt out?

It may be, of course, if you're using little enough power that nothing else is suffering, but it's not a particularly good idea to run any amp with any dead finals, as most likely if it's actually dead you'd be overloading something, or putting a big DC imbalance into an output transformer, etc.

But don't touch it, etc, to see if it's warm (it could be *H*O*T*, etc), or dig into the guts of the box, warm or cold, since you aren't familiar with tubes. This could be bad for tubes, hardware, or you. So don't.

Somebody who knows your particular hardware will likely come along with more info.

Edited for bad spelin

EL34's are cheap...get a new one and do not operate the amp till you do.

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Why do I think it's burnt out - the tube no longer lights up. The other three are all lit at the tip of the fuse inside, but not this one. All four were lighting up as of two days ago - just noticed it today. I assume that the PL's auto-biasing may have something to do with the fact it's still functioning without a problem.

That does seem definitive, since you have seen a change. The "fuse" you refer to is the cathode heater, by the way.

I go with the "buy new tube, do not use" crowd, then.

If you haven't already placed another tube - one from the other side of the amp - in place of the "defective" tube, you should make certain the problem is with the tube and not the circuit in front of the tube. Swap tubes with the amp powered down.

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If you haven't already placed another tube - one from the other side of the amp - in place of the "defective" tube, you should make certain the problem is with the tube and not the circuit in front of the tube. Swap tubes with the amp powered down.

AND COMPLETELY COOLED DOWN. Burns are no good. Cracked tube envelopes are no good, either.

Best to handle the tubes with a clean, soft cloth, even when cool, too.