Are we talking hum with NOS tubes, hum with new production tubes, or just hum in general w/ or w/o tubes?
Tubes in general, especially NOS tubes, or previously used old tubes can add hum to the equation. Often the culprit causing the hum are dirty pins. Clean the pins with alcohol and for especially grimy pins, I've used sandpaper, Deoxit, alcohol (in that order) with good results.
Other Glenn owners have reported good results using a dremel on the pins.
If the hum still persists, its time to toss the tubes and buy more. Life is too short to deal with hum.
EDIT:
Research carefully how to use Deoxit, alcohol or any other solvent on tube pins. Never ever, EVER insert damp pins into a socket!!!!!