I have found that a lot of hum from amps can be caused by power supplies. If you have the amp plugged into a power bar or some other type of cord, try plugging it directly into a properly grounded wall outlet. I had a loud hum suddenly appear in one of my amps. I tried everything to get rid of it and was pulling my hair out. I tried it with another amp in the same room, and got the same thing.
I thought it might be my pedal board, so I checked every pedal and cord, and still the hum.
After about 3 hours of wracking my brain,a thought hit me. My pedal board has a built in power supply so I thought it might be bad. I went to unplug it and found it plugged into a power bar that I use for my stereo.
My wife had done some cleaning and unplugged it from the wall to plug in the vacuum cleaner and plugged it into the bar. I put it back into the wall and the hum was totaly gone.
If that does not work, being an orginal 72 it is worth taking to a good tech. You can spend a lot of wasted time and money trying to trouble shoot the amp, when it could be something simple. Of course it could also be a 20 dollar tube, as suggested already.
The Blues is alright!
Guitars: 1968 Gibson SG, 2005 Gibson SG Standard, 2006 Gibson LP Classic Gold top, 2004 Epiphone Elitist LP Custom, 1996 Gibson Les Paul Standard. 2001 Epiphone Sheraton II, 2007 Epiphone G400.
Fender Strats: 1996 Fender 68 Reissue CIJ, 2008 Squier CV 50s, 2009 Squier CV 50s Tele Butterescotch Blonde
Amps: Blues Junior Special edition Jensen in Brown Tolex with Wheat front, 65 Deluxe Reverb reissue,1970 Sonax reverb by Traynor, Avatar Custom 2/12 Cabinet with Eminence Legend V1216 speakers,
2008 DSL100 Marshall Amp , Fender Super Champ XD,Fender Vibro Champ XD
Effects and Pedals: Fulltone Fulldrive II, Fulltone OCD, Fulltone Mini Deja Vibe, Fulltone Fat Boost, Dunlop Crybaby Wah, Boss DS1, Boss DD20 Giga Delay, Boss TU2 tuner, Boss BD2, Ibanez TS9 Tube screamer, Zoom 505. Radial tonebone hot british.