The TSL built a HFL device using primitive germanium power transistors in 1967. I believe the transistors were 2N174, if you can imagine such a low number. You had to keep them cool to avoid thermal runaway, so we had some feedback windings to make them switch fast and run cool. It worked so well that we blanketed the AM broadcast band in the near neighborhood and had to back off our feedback, letting them run a bit hotter. A typical DCC power unit puts about 14 volts at 8kHz on the tracks.
Smoke happens as soon as the motor power adds a bit of heat.
Limit it with a capacitor, rectify it, and charge a single nic-cad cell for flicker free caboose markers lights. Dramatically improves occupancy detector performance. How do we build it. Lynn Westcott of Model Railroader asked me to write an article on it back in '72 or '73. Unlike the original on the TSL, this one uses a convenient regulated DC power supply from our junk box.