Marshall tsl 100 head loud Clean Channel Hum after it heats up after few minutes on

[HolySmoke]

I tried re placing 12ax7's did not stop hum? Help.. HolySmoke...new user here

[blindboybenton]

Hi

Try to swap the output tubes. post the voltages. Could be a bad filter caps. Is the amp working ok loud ?

[Dave Curtis, dB AudioTech]

If you don't know proper procedures for taking voltage measurements, find someone who does. Otherwise, shut the room lights off and look at your output tubes as it starts to hum. If they're starting to glow cherry red, shut 'er down. You've lost your bias, or it's wonky, or possibly a bad output tube... First/easiest thing to rule out.

[Mick Bailey]

If hum is only on the clean channel it's unlikely to be the output tubes or filter caps as they are common to all channels - it's something to do with the clean channel. Any power supply or output tube hum will be worse on the high gain channels if it's filter caps.

Does the hum go away with the clean channel volume turned down? If it does the problem lies before that control. Does it hum with the guitar unplugged? You need to find out if any controls affect the hum.

Serious mis-biasing will cause hum due to loading on the filter caps increasing ripple. But again, this would affect all channels and not just the clean. Always a good idea to check the bias on these amps anyhow.

[Enzo]

Or is the hum on the lead channel too, but we just never use that channel?

He didn't actually SAY it was only the one channel. Believe me, I am not being picky, I get such descriptions from customers all the time.