I give up! Ive had my JCM2000 dsl401 for a little over a year now or so. About 2 months or so after I got it, I changed out the preamp tubes (they were original). Finally this past August/september, I changed out the power tubes with a matched set of JJel84. I also biased the amp myself to factory spec (followed a write up from around here). When I changed the tubes out, I used a quick dry contact cleaner to clean the tube sockets. I’ve noticed recently that there is a faint crackle most noticeable on the clean channel, and also a hum that’s is inconsistent (sometimes it’s present from right when I turn the standby switch off and start playing, sometimes it takes a few mins to start... here lately it’s started right away and goes away after a few mins.) Ive tried plugging straight unto the return jack of the effects loop to bypass the preamp.... noise is still present. Ive tried taking all of the tubes out, recleaning with contact cleaner and trying again. Ive tried tapping on preamp tubes, etc to no avail. Anyone have any ideas about what to do next short of buying another quartet of el84? It’s very curious that this started shortly after I changed those power tubes out. Any help would be appreciated.
Forgot to add that while troubleshooting, this reported crackle and hum is present even if absolutely nothing is plugged into the front, or the effects loop. My next step is to put the old power tubes back in and see if it’s still doing it.
Here’s a quick video. The hum gets louder on the clean channel the higher the master volume is. I also noticed that when I turn up clean gain all the way it’s hard to hear it. Can’t really hear much on the overdrive, it’s noisy as is.
1. Crackle is most frequently a bad preamp tube. Buy 1 new tube and swap out the tubes one at a time with the new tube. Then re-test each time you swap one out. If there is a bad tube you can find it. You do not need to buy a whole set of tubes to find a bad tube. 2. Plug a guitar cable from effects send to return (if there is an effects loop). Now re-test. Contact cleaner: Lubricated non conductive cleaner is recommended. This will coat metal and slow oxidization. Also may break up existing lighter oxidization. Deoxit G 100, D 100, or LPS-1 is recommended for jacks, sockets and pots. 3. If you have re-tubed tested as above and cleaned the jacks/pots/sockets, bypassed the effects loop and still there is no joy... Then you have reached the limit of what a consumer is able to do. Then it gets more technical. 4. Pull the V1 preamp tube, turn the amp on. Turn up the master all the way (if there is one). * V1 preamp tube being the tube closest to the input jack. Is the noise still there? Put the tube back in.... 5. Plug guitar into amp, wiggle plug where it enters the amp. Up/down/left/right gently flex the plug in different directions. Does the crackle increase? Does the sound cut out? Broken solder connections at the input jack.
I bought 4 new preamp tubes back in December. And one new tung sol for v1. I swapped the one older preamp around and it’s still doing it. Am I correct to understand that if I plug into the return of the effects loop this means it’s not a preamp tube? What about the humming?
It’s never happened before is what’s weird, and goes away and comes back intermittently. Aside from that the amp sounds and plays fine from what I see.
Ohhh I can hardly wait............................................................................................................... antici.................................pation.
Sorry.... I do appreciate your help. It’s still doing it. Subtle crackling .... didn’t hum that time though. V1 is a new tung sol I bought end of August.
Nope. Was quiet for about a minute, then it started. Still no hum. Possible I need to reclean these sockets again?
Put in 2 output tubes into the middle 2 sockets 0XX0. X00X is OK X0X0 is OK 0X0X is OK. Swap output tubes around and see if 1 particular tube is crackling. Swap sockets around and see if crackle is associated with one particular socket.
