Spare tubes? How many?

Any tube can fail, especially if you don't have a spare.

If you have individual biasing pots for each tube replacing the blown one and rebiasing it works fine, so long as you're not too anal. You don't need to replace the other three. Now if the tubes have been used a lot you can replace the entire quad and have 3 'spares' for future failures. :-)

Seriously, the small tubes die unexpectedly, even though they typically have a long life. At least keep a few new production tubes available to keep you in music until you can get some replacements.

Of course it's easy to get carried away in this process.

I have one amp which uses a quad of KT88's. So I bought a spare quad. They were a different brand. Tried the spares and liked them MUCH better. Then I bought a new spare set (different brand). Tried them and liked them MUCH better... I think I'm up to 5 quads now hanging around. And of course I've got a set that I truly love in the amp, and lots of sets that will work, but no same-brand replacement as my favorites.

It's a slippery slope if you start getting into tube rolling while buying your spares! And that's without considering all the perils of NOS tubes. Saw a nice set of Genelex Gold Lions going for more than I paid for my amp!

Fair warning!

Thanks all...looks like I need to start budgeting for some backups. (Dfhaleycko - Thanks for the warning. Ain't going down that path! I'm running upgrades over the stock tubes now. Should be able to order same same for all 3 types).

I guess I am an tube hog... :-)
I have four extra pairs; but they are vintage 1940's tubes so worth keeping...