It is a Peavey "Classic" and would be the A series. There are four input jacks, two bright and two normal. That is the A series. A B series Classic has four jacks, but they are one each bright, normal, series, parallel. Not what you have.
Your amp uses two 6L6 power tubes. The B series schematic at SChematic Heaven is not for your amp, but if you look, it does say 6L6GC for the power tubes, not 6L6C.
ANY 6L6 currently on the market is perfectly fine for your amp.
Historical note: the original 6L6 tube was a metal tube. You can find these here and there today. They are NOT suited to guitar amps and have much lower ratings than modern tubes. But that is plain 6L6. A long time ago they made the glass version of the tube and it was the 6L6G - G for glass. Later, improved versions came out, the 6L6GA, the 6L6GB, and finally the 6L6GC. Good luck finding a 6L6GA. You probably can find NOS 6L6GBs out there, but don;t waste your time and money on them for this amp. 6L6GCs are made today. You can also find things labelled 6L6GB on todays market, but they are really not "real" GBs, and they would work fine too.
You want some letters? I think the Ruby Tube 6L6GCMSTR is a real nice solid tube that is happy in this amp. But the common SOvtek 6L6 family of tubes would be fine, or any one of a number of current brands.
Customer service at Peavey will send the schematic upon request. But here it is.