Marshall TSL100 Volume cutting out

[eonblue]

I have a Marshall TSL100 amp head and a Marshall 1960B straight 4x12 cabinet. I have had troubles in the past with the volume losing power. Could this be because of the amp head getting too warm? I have not had a problem with it since I placed a fan to blow no the amp head from behind. I am not pushing it anywhere near full power. If anyone knows what the problem might be or if it is because of temperature, I would really like to know. Thanks.

[Thorny]

don't overlook cleaning the FX loop - that'll cause it to cut out (although the fan won't help fix it).

Make sure it is biased correctly and that it does not drift too much. If your tubes grey plates turn red hot - you have problems (biased too hot, bad tubes, or something else).

The DSL amps have tones of problems with the diode/rectifier assembly overheating and cracking solder joints on the board. I don't recall this problem on TSLs though.

[Mars Amp Repair]

Also,
Yes, the effects loop switch in the return jack can cause signal loss.
'fairly standard troubleshooting here;

1. try pounding on the top of the amp with your fist to see if the issue is a bad connection or possible intermittent tube....really! . Also removed the tube shields & lightly tap on the 12AX7's to see if you have any intermittent ones. You can experience microphonic tubes & that's probably ok.

2. You might try to isolate the pre-amp section from the output by going from the TSL send jack to another amp & see if the volume drop is evident in the other amp. If so, your issue is in the pre-driver stages.

If not, then it must be in the driver/power stages.

As I recall this amp has switches to engage the FX loop jacks. You might try pushing them on & off quickly to determine if they're dirty.

You can also just jump from send to return & see what happens there.

Does pushing the VPL (I think that's what they call it..Virtual Power Level) switch change things much? Also the power Mute switch ckt could be suspect.

I have had major biasing issues with the circuits around those 2 switches. Mostly cause bias issues & eating tubes.

glen