How does a Tube Rectifier fail?

[harry]

Never had an amp with a tube rectifier before, so I don't know how they behave.

I'm making an amp with a 5AR4, the power transformer secondary measures 720V ac with a meter (is this commonly labelled 360-0-360?). after rectification it produces 390V. I checked voltages a while ago without tubes and it was giving out 520V.

If I monitor the plate of my EL34s as I play, the voltage slowly drops. I imagine the amp would fade out completely eventually.

So my question is: when tube rectifiers die, do they fade out slowly?

[Baxtercat]

I had one go in a Super Reverb [decades ago, before I knew any of this stuff] and it glowed red and took out some filter caps too. It must've had a short.

[Enzo]

Does that voltage continue to drop? Or does it only drop a certain amount as the amp warms up? And does the voltage climb back up when you stop making sound through it? That would be normal.

[harry]

It continued to drop.. maybe a volt every thirty seconds.

Today it gave up completely and began arcing. Oh well.