I’ve build this amplifier using 2 QQE03/12 VHF power amplifier tubes. A QQE03/12 is a double tetrode, so you need 1 tube per channel. And 1 ECC82 or so as preamp and phase shifter. The output transformers I bought via the internet. They came without data and with lots of wires, both primary and secondary side. Using a function generator and a scope I determined the corresponding set for 3k/4Ohm.