Matchless Spitfire transformer hum? What the?

[gtrnstuff]

After warming up, the power tranny hums, the chassis vibrates, and there's hum at the speaker. Nothing plugged into input. It's not so bad it can't be used, but should it be repaired?
FWIW a Lightning about the same age (new in '97) doesn't hum, just a bit of hiss.

[suhr_rodney]

Odd... mine does not hum. Perhaps it warrants a phone call to Phil @ Matchless.

[gtrnstuff]

On a whim, I swapped out the rectifier tube and the hum dropped a LOT.
So in spite of what I've read on the internet :-), a rectifier tube can exhibit qualities between "working" and "not working".

This was confirmed by an email I got from Phil at Matchless. He said even new out of the box 5AR4 can cause that.

[mr coffee]

when the bias is off and also as loose PT mounting nuts..