Filament source (T398E)

Despite being transistorized, this is a constant current source circuit for 1 V valve filaments such as the 1H4 tube.

Record Head Preamplifier (CB4949E)
This 80's circuit can be used in media recovery. The integrated circuit is of the time, but modern...
Balance Indicator (CB5021E)
This circuit is from the American magazine that no longer exists Science & Electronics,...
Quail Brooder (CB4467E)
This circuit, from a 1988 documentation, consists of an automatic temperature control using an NTC...