Help with marshall jtm-30 & 60

[Force235]

Hi, I am new to this website... I have two Marshall JTM combos a 2 x10" 30 watt and a 1 x 12" 60 watt, they are both exhibiting problems when I play the amp in the over-drive mode (channel). Basically the gain simply goes away and it become clean, then a few seconds later it jumps back to high gain. Has anyone experienced a similar problem and are you aware of a fix?

Both amps are 1995 and 1996 vintage.

[metalangst]

That may be an issue with the switching circuit. Bad relay contacts, or a dirty contact on the switch that controls the relay. I'm not familiar with those circuits, but if you can switch with a pedal or not, try both.

[Amp Kat]

When it does this look at the back at the tubes and see if the tubes heaters (orange light) are going out and then coming back up. This is a common problem with these amps and has two fixes. Either the rectifier needs to be changed or the tube sockets need to be soldered from a cold solder joint. Bad power tubes can cause this also. That amp uses 5881's and most 6L6's won't fit in it or at least the cage won't go back on right.

[Force235]

Reply

I read the other similar threads, I checked the tubes when in use, I did not notice any problems with the glow on the tubes. The heaters )for now) appear to be ok. I tried working the pots, I need to buy some contact cleaner and spray some in. I also worked the loop 1/4" jacks . I then let the amp sit until the following evening, of course that shouldn't matter, anyway the amp played perfectly. I will also try using the foot pedal to switch channels, I'm not sure if my problems are gone but they were last night, I'll keep you posted. Thanks for the help...