50 caliber plus hum problem.

[bertie]

Hi all
I`ve had a 50 caliber plus combo for almost a year but had a few problems, most have been sorted. However, the last remaining one is a hum which is most sensitive to the lowest frequency slider on the graphic. It only occurs on the clean channel though. Any ideas? My amp tech has exhausted his ideas with this one.
Thanks.
:?

 

[bigbean]

Did you try unpluging the reverb tank to see if that makes a difference?

What have you had done to it so far?

 

[stokes]

How old is the amp?Is the hum there with no guitar plugged in?Does the volume controls affect it?