I know this is only a toy, but the cost of transformers has been increasing, and I wanted to build something that would theoretically withstand an EMP or Carrington event (no solid-state) just to see if I could do it. The 117N7 was developed it seems, to provide regulated DC filament voltage for a string of battery tubes.

I am trying to make a simple 40 meter tube transmitter. The first step is two tubes and CW. The joker is that I am using NO power transformer and 117N7 tubes. The box is wood and the panel plexiglass. By using a small inside isolation relay with 9 volt battery and key jack located outside the enclosure I can key it safely. Power entry is setup for three-wire with IEC connector.
The crystal oscillator is a Pierce circuit, so no tuning is needed on that stage.
The output is the problem. A regular PI network needs to bring out the ground side which violates my safe transformer-less parameters. I tried a toroid tank circuit link coupled to the antenna connector, but the low (120 V) plate voltage made the calculations off the charts in the old books. Everything up to the plate of the keyed tube is old reliable, but I can't seem to get more than about 1/4 watt out of it with the varied tank circuits I have tried. Swapping tubes gives no change. Your suggestions are requested.
Thanks,
Pat

Pat, that's fun! Attached are a couple of files on 117L7 tube transmitters that might be of educational and scientific interest to all.

Should be able to deliver a couple of watts. Output will be in the neighborhood of 5K ohms; assuming you want to match it to 50 Ohms, that's a 100: impedance ratio or 10:1 turns ratio. Powdered iron or low-perm ferrite toroid should do fine - primary tuned to 7 MHz, secondary insulated Teflon wire.

Pi network needs circuit common isolated from output ground with a capacitor, a ceramic Y-capacitor should do OK at this low power level. And likewise "hot" RF output needs an isolation cap (.01 "Y" caps are 2 Ohms at 7 MHz; should do)

Thank you both, I now have somethings to try this weekend.
Pat

Here's another: https://worldradiohistory.com/Archive-Poptronics/50s/58/Pop-1958-05.pdf page 77. And it only uses one tube. Definitely a shock hazard.

No, it provided unregulated voltage and only for a few tubes if they were used in the cathode circuit of the beam power section. For a normal superhet, there was the 117Z3 and 117Z6 which were only rectifiers. Tubes like the 117N7 were mainly used in "one tube wonder" phonographs and other similar low cost products.

1958 is a year after I got my license. It is a good thing that I never saw the POP-TRONICS magazine of that year. (above) . Not only did they put full DC on the antenna, They switched the ground and had no fuse.
Thanks for the reference.
Pat