Filament source (T398E)

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

PH meter (CB5324E)
This circuit is from an 80's documentation. The circuit makes use of a component of the era, the...
FM Receiver via Power Grid (CIR25197E)
Unlike the previous one, this circuit is intended for the reception of frequency modulated signals...
4 Channel Mixer (CB4921E)
This circuit is from an old National Semiconductor component manual. The circuit can be...