Attached are pics of an amp I just finished (well almost) that uses a pair of 13GB5 sweep tubes in push pull configuration, a long tail pair phase inverter using 8GU7 tube and 4EJ7 tube triode connected as the preamp. The output transformers are Atlas HT327 line transformers that reflect a 1200 ohm plate-to-plate impedance with 8 ohms connected to the 4 ohm tap.
I'm running 220vdc on the plates of the 13GB5's and 170 vdc on the screens (via two series connected #5651 gas regulator tubes). Bias is zener diode regulated, presently set at 80 ma per tube.
The Phase Inverter and preamp supply are run off a voltage doubler to make enough voltage for direct coupling between the preamp (4EJ7) and PI tube (8GU7).
Amp is built on a Dynaco chassis with Geek's "Dynamull" driver board (but 4EJ7 triode connected, not pentode as Geek designed it).
A quick check (needs to be verified), seems I'm getting about 25 watts per channel. Negative feedback is connected but I need to go back and calculate the amount I'm using. I also need to add the feedback cap.
I'll clean up and post the schematics later.