How do you know when tubes are done?

Hi,
tubes are towards or end of life when dynamics are gone. Preamp tubes may produce funny noises or extra hiss sound, power tubes will lack power to drive efficiently. If in doubt get or borrow a good tube tester and check before rather than sorry later.

roberjerman you are showing your age! Heathkit? Us Dynaco guys use to sneer at the Heathkit guys but you had to be braver to do a Heathkit because you had to build the boards, Dynacos you just had to do the point to point wiring. Bravo! I wish manufacturers would offer kit versions of their stuff again. Anyway, I always keep a spare set of tubes on hand. If you think something is off you can always swap to make sure. Actually, I always keep a spare set of everything around which I think is a neurosis. I would have a spare wife but I'd get shot. Think of what would happen if I got Atma-sphere MA-3s. I would be buried in tubes then get shot.
Steamboy with less gain in both channels I would suspect a power supply problem. Check your voltages. Great that you built your own stuff!

Change all tubes asap!!

Thanks everybody for the help.

Now I have to find a tube store!

And check the power supply!

I didn't make these myself. My landlord, David Yee, built these from scratch. He gave me several amps and pre amps to try and I picked the ones I liked best.

I can find no trace of him now and I wonder if he's back in Hong Kong.

He found Vancouver "too slow"! He called himself "DavidYeeAudio"

all posters gave good advice. IMO, the best was to keep a replacement set on hand at all times. If your tubes sound "tired" the new set should easily allow you to hear a difference.