question for those with tube amplifiers.

[Sonic101]

I have a Marshall JCM2000 DSL50 with all MESA tubes, 2 EL34's for power and 4 12ax7's for preamp. I run that through an old Peavey 412m cab. I play through the clean channel(not the crunch channel) and use stomp boxes for all other tones. Recently I've noticed when I'm not doing anything there's occasionally a light metronomic ticking sound that stops when I touch my strings. I've tried it with 3 different guitars and this still occurs.

In the last 2 days when I strum a chord hard, I get a farty crackling sound when playing straight clean. I thought I might have a bad speaker, but all 4 speakers seem to sound normal when I play at bedroom volume levels. It's much more noticeable when using either of my Les Paul's on the treble setting but gets much quieter if I switch to the rhythm setting on the guitar. I couldn't here this problem though using my telecaster.

Next thought was maybe it's bad tubes, so I cranked the amp volume and began tapping on each tube. One of the pre amp tubes (in the V2 slot) makes the same thumping sound you get when you tap on a microphone. you can hear it through the speakers. The others not so much.

Any advice? I've only had the tubes replaced once about 6 years ago just to be safe after buying the amp used. It got used maybe a month after that retubing before being put in a case and sat in a closet for 4 years until I brought it out and then for the last 1.5 years it gets played at bedroom volume levels 4 or 5 times a week for a few hours.

[rireland]

Try swapping the suspected bad tube with one you don't use (you said you don't use the crunch channel) to confirm it's dead

[Andy92]

Preamp tube going bad.

[Sonic101]

Should I just replace the one tube or all 4 pre amp tubes or go for broke and retube the whole amp?