Are you sure the hum isn't real? A lot of solid state
devices trash up the power line. Rectifiers are a big
source, lamp dimmers and fluorescent lamps are another.

Barring that, look for heater cathode shorts from the
detector tube back to the power amplifier tube.

-Chuck

Antonio Vernucci wrote:
You sure the power supply filter caps are good?

Please read my self-reply.

Tony I0JX