I sent my info to Peavey on the amp and they said this IS a hybrid amp. This came out right around the time they started making their tube/transistor amps. This amp was also one of the first to roll out in the 70's. Before they added Master Volume, Tube Preamp, and some other features. They also said they made about a dozen ss preamps/tube power amps.

S.S Preamp
Tube Power Amp

Im guessing he is right since he is one of their techs and i dont know much about tube amps.