Despite being transistorized, this is a constant current source circuit for 1 V valve filaments such as the 1H4 tube.
This circuit was found in a Electronics Handbook (1989). The shown amplifier provides a few...
The SCR used in this 80's circuit depends on the load. The control is half wave and instead of the neon...
This circuit was found in Delco documentation from 1966. The components are from that time....