Filament source (T398E)

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

Time Relay (CB12432E)
This simple timer is from a 1998 publication. Other operational amplifiers can be used, and the...
Manual Heater Control (CB21276E)
Found in an Electronic Design from the 90's, this circuit uses an SCR according to the controlled power....
Product Detector (CB15635E)
This circuit decodes signals received in SSB (Single Side Band) obtaining an audio signal for...