This transmitter runs dual 6L6WGB (5881) tubes configured for push pull operation. The article is from pages 18 to 24, of the "Jones Radio Amateur Newcomer", and it says the rig will put out about 50 watts, if you run 400 volts on the plates!

Initial reports indicated that the rig had quite a bit of chirp. This was cured by removing all but 2 turns from the coupling coil. Measured output shows 7 watts.

This is the plate coil with a center tap at 11 turns, before the coupling coil was placed over it. The (350 volts) B+ comes up through the wood base to the center tap.

Completed rig less coupling coil and antenna.

Here is the coupling coil placed over the plate coil with the tuning lamp in series with the antenna.

Here you can see the 350 volt power supply, Heathkit HR-1680 receiver, and the t/r relay.