Sounds like a bad tube. Are any of them glowing red after being on a while? By "a fuzz" do you mean a hiss, a hum, or exactly what? If it's a loud "white noise" type of hiss that sounds like an FM radio between stations, and starts a few seconds after the amp is switched on, it could be a bad rectifier diode in the power supply. They can still work and yet go VERY noisy all at once, so noisy the amp can't be played. A hum could be a bad power tube or a blown filter cap, although a bad filter cap is unlikely unless your Classic 50 is one of the earliest models and the caps are getting old. Though your Peavey's Illinois Capacitor filter caps are definitely not the last word in high performance, they are very robust and reliable, and besides are well overrated for the voltages in the power supply.
Hope you find that problem quickly!
Thermionic