"Fixed" bias versus "auto-biasing"

Thanks to both Kehut and Banksfriend for your responses. I appreciate the input. Can either or both of you tell me briefly about tube replacement when the amp is auto-biasing. That is, I assume that a single tube could be replaced if necessary rather than having to replace a pair or a set of four? With an auto-bias amp, is it even necessary to purchase "matched" tubes should one tube only go bad? What kind of tube-life should someone expect, generally, or is tube degradation something I'd recognize without much trouble?

Arkprof, what amps are you considering that brings up this question? Many tubes are both long lived and inexpensive enough that this issue should not be a determining factor -unless your talking about matched B300s etc.-?

That is one of the other advantages of auto bias..you can replace one tube when it goes and not a whole matched set of 4. It becomes less critical to have your tubes matched..but I would still recommend matching so that the bias circuit doesnt have to compensate too much.

Most amps are now fixed bias with auto biasing less popular today. Mike Saunders at Quicksilver is a proponent of auto and uses this type in many of his amps without problems.Ive used several of his nice amps.

I echo Banksfriend's question of what amp(s) are you looking into?

With auto bias, the tubes will be continually biased as you go..sonic degradation will occur towards the end of the tube life and then the tube will be so weak, that the auto bias circuit will not be able to bias it anymore and it will sound that way! or just give up the ghost.

You will have to adjust the bias on a fixed amp on occasion, usually a check every 3-6 months is good and adjust as necessary.Some tube types like the 300B require check fairly often...others like the EL84/6BQ5 much less often

Again, this kind of info has meaning for me. Over the past 7 years I've gone from two different Classé amps to two different Pass amps to, this past year, a Pathos Classic One/Shanling SACD (tubed output) combination. I want to slip into tubed amps/preamps, so I'm starting with an Almarro A205A, but I'm currently using a small Sophia Baby amp until the Almarro gets here. Cain&Cain speakers (95 dB). I realize that quality will be defined to some great degree by dollars invested, but the Sophia makes it clear to me that I'm going to enjoy tubed gear and I have greater expectations from the Almarro. Neither amp is expensive, of course, but I'm thinking I'll find what works for me without having to fork out too many dollars (PrimaLuna seems to get lots of good press, though Almarro does, also). I don't really want to spend more than $2k nor have something that could warm my entire house.

All of my questions simply reflect some underlying doubts or concerns about tubed amps ... I guess I've always sensed that they might just be one ongoing headache ... tubes burning out, noisy interference, way too hot, too fragile, etc. I think I was greatly misinformed.