I have had my amp JCM 2000 TSL 122 combo for a few years. I used it occasionally when I first acquired it (around 2008) and then fairly regularly in a band for about a year in 2009/20010. It was then put in my wardrobe and came out to use ocaasionally for a couple of gigs and then went back in the wardrobe until earlier this year.

In 2016 I have gotten together with some friends to form a new covers band and we have rehearsed at pretty big rehearsal room volume with live drums etc. at an average of 2 rehearsals a month since March.

Today, I started to set my amp up as usual - plugged in and turned on with standby. Took off stanby with all 3 channel gains and volumes at ZERO. 1st channel (Clean) some gain + some volume (uaual position around 2 and a bit....rarely get it to 3, haha!) and it made all the usual signs of working well and giving me a great clean sound.

Turned to the other guitarist for a quick conversation about pics he bought on e-bay and I found my volume dropped!!??!!

I checked leads, connections, another guitar, but my Marshall is not doing what it has been doing. Our other guitarist put his guitar through it and it needed almost full gain and full volume on each channel to get any volume on the output.

I turned ot off and used an amp that the rehearsal studio had available. Effects and leads all good, so the issue is definitely the amp.

Am I experiencing a dead valve, or set of valves, or could it be something more sinister? This is my first valve amp and appreciate that these things are much more sucsceptible to issues and need much more maintenance than their solid state counterparts.

Any advice on this would be much appreciated. I have searched the issue and found that there are some sites with negative thoughts towards the JCM 200 series and the TSL 122 in particular with biasing issues etc., but what I am reading is going over my head a little, but looks quite damning???

Thanks for any help,

Graham