I had my Classic 50 at rehearsal last night. With the gain up on the lead channel, I was occassionally getting this high-pitched whine coming from my amp. I only noticed this when I wasn't playing and it only happened a couple of times. The tubes were replaced 1 1/2 years ago and I gig 3-4 times a month.
Does this sound like a mirco-phonic tube? I've heard of this problem but have never experienced it. If so, is this a sign a tube is going bad? Does this happen with pre-amp tubes, power amp tubes or both? Do I need to change the tubes now or is this something that is a characteristic of the tube?
I usually have my amp set up relatively clean and use pedals to get my dirt, but last night I didn't bother taking my pedalboard to rehearsal and had the gain up on the lead channel to get the dirty tone.
Any advice is greatly appreciated!