Hi just joined this forum as I'm having trouble with my amp and thought someone might be able to give me some insight into how to fix it. I recently bought a Marshall valvestate as not working (only £20 so worth a shot). The overdrive channel was very quiet but would sometimes cut back in at regular volume, splutter a bit and then cut out again. The pots were noisy too so I  sprayed some cleaner in them and replaced the ecc83. This fixed the problem and it started working fine, except for when the volume would occasionally drop as it did before the valve was replaced. Hitting it always worked to make it cut back in though. A couple of days ago during a rehearsal there was a popping sound from the speaker and the amp cut out entirely. It powers on okay but the only sound I can get from it is a low hum/buzz from the speaker which remains constant regardless of what any of the controls are set to (volume and gain controls neither reduce nor intensify the hum, it is just one constant volume). Plugging a guitar into it makes no sound at all and also does not affect the hum. Touching the tip of the jack lead whilst the other end is plugged into the amp also makes no sound and I've tried a couple of cables. I've checked the bottom of the pcb for any dry or cracked solder points and can't seem to see anything wrong. Any ideas as to what could be wrong with it?