First of all marry Xmas.
Hi,
I recently build JCM 800 2204 type amp model. The amp works fine but there is noticeable hum. When you turn preamp pot down you should hear nothing from the speakers, but there is a hum when pull up volume pot.
I think that hum comes from power transformer because I made it by my self. It is old soviet transformer TC-180 I re-winded it.
Maybe some advice how to reduce hum.