Hey guys, lately my 6505+ 112 has been making this loud hum sound whenever I turn it on, and the Peavey logo doesn't light up anymore. A couple weeks ago, the volume was fluctuating all over the place, so I kind of assumed the tubes were ready to go, but I never got around to changing them.

This is my first tube amp, and the first time I've had to switch out tubes, so I'm a bit of a noobie. Which tubes would be the culprits in producing all the symptoms listed above?
The logo is lit by 6 LED's on a small board behind the logo. There is a separate power wire to runs from the amp into the board. You could take off the front panel, unscrew the back logo, and expose the board and replace the LED's if you want the logo to light up again. I removed the wood block/logo and put in a stereo light strip behind the reverb tank in my combo, there's pics of it on my profile.