My brother-in-law's hot rod deluxe had hum problem. HE called me to check it out. Amp starts up with no noise, then gradual increasing hum. Cleaned and tightened chassis grounds. No good. Took chassis out for better look see. Noticed one 6L6 plate increasing glow to red hot, as hum got louder. THEN HE told me HE had just re-tubed with Grove Tubes and re-biased using bias test voltage method. NOW I'M WORRIED ! Checked test point and found ZERO voltage ! Before shutting it down, there was also distortion and slight motorboating while playing guitar. He says all was well BEFORE he replaced speaker. I haven't swapped 6L6's yet, but don't think it could be a bad tube.
Visual inspection shows NO burned spots anywhere. New Eminence speaker(8 Ohm) seems O.K., tested resistance at 6.8 Ohms. I have some experience at repair and modding tube amps, but I haven't come across this before. I have reference books that I will check, but he has a gig to play end of this week.
If anybody has knowledge or advice to share, I would be forever grateful(and HE should too). PLEASE help ! tonequester.
P.S. I apologize, as I don't know how to post a schematic, although I found one.