KEL84: Humming, growling, screeching and screaming

[Sid and Coke]

Hello folks,

Just had a weird one with my KEL84 and not for the first time either.

My amp stays turned off most of the time when I'm not using it. I only turn it on a few minutes before use, but then will keep it on all of that day ( or evening) until i go to bed at night, or leave for work usually at about 8:30 pm ( permanent night shift worker).

I turned it on this morning and an unholy racket issued forth from my speakers. It was a very loud grumbling and humming sound. Turning the source select to 'mute' ( and all the other selections ) had no effect, also turning the volume down to zero ( or any other setting ) also had no effect.

I switched the amp off at the mains switch and the noise eventually stopped.

I gave all of the valves a 'wobble' in their seats, to hopefully give the contacts a bit of a clean and tried again. The noise returned but this time was more severe, on switching the amp off again ( panic mode on) the speakers were screeeching and screaming very loudly ( source @ Mute, Vol @ zero).

I removed the two Brimar ECF80 and re-fitted the original EI ECF80. switch the amp on and everything was quiet as normal. I tried the two Brimars again (after gently dropping the onto the floor carpet to give them a bit of a jolt) and again the amp worked fine with no horrible noises.

This isn't the first time the amp has made uncontrollable noises such as this, which is a worry, especially if it is left unattended as i fear it might trash my speakers.

Any idea's ?