How can you tell if a rectifier tube is dying?

[LivewireBlanco]

Never really seem to find the answer to this one. Anyone?

[SteveD]

A rectifier valve usually either works or it doesn't. If it has mechanical damage but still works electrically I suppose it could propagate extraneous noise on to the HT.

[LivewireBlanco]

Thanks Steve! What would we ever do without you?

[MKB]

I've seen only one bad rectifier tube in my life, it was a General Electric (actually Mullard made in UK) 5AR4. It must have had an internal short as it caused the power fuse to blow, which is a BAD BAD THING. I've tested quite a few other tubes and even the really old ones tested OK.

Moral of the story is: use NOS rectifiers when you can, they last an extremely long time. But if you at all suspect one is bad, change it immediately as it can cause lots of expensive damage.

Some of the newer manufacture rectifier tubes aren't as reliable as NOS, but you can very simply modify an amp so that shorted rectifier tubes can't harm it. You basically put a solid state diode in series with each section in the rectifier tube; this allows all the good sonic stuff you get with a tube rectifier, but even if the rectifier shorts out the diode keeps it from smoking the power transformer. Several boutique manufacturers are doing this now.