hi,

one of my 2A3C valves is displaying strange behaviour:

last night I was sat quiet with the amp switched on. All of a sudden, a 2A3 valve went really bright, there was a slight 'pop' from the left speaker and a sound vibration from the amp like a quiet hum.

I switched it off and left it until today, this afternoon it was fine again!

Anyone actually know what this means/indicates please?

cheers!