811A Push Pull, Zero bias tubes. Old power transformer used as OT. The frequency response is far from perfect, but that is nothing an EQ can't fix. A proper OT would solve that issue and provide more output power as well. But they cost a lot of money that I don't have. I got these tubes cheaply from some seller locally. 680-700V on the anodes. Driven by Zenith SB23 with quad EL84 push pull output. Sounds mighty good, and more than loud enough for anything! All speakers except the double-10's are hooked up, because I simply do not have enough cables wired correctly. Load impedance is about 2 ohms. Amp delivers best power at around 1-1.5 ohms. Directly heated triode goodness!