Filament source (T398E)

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

Millivoltmeter with the 709 IC (CB24208E)
This circuit was found in the September 1972 issue of Radio Electronics magazine. The circuit uses...
62 mW Stereo Amplifier Handset (CB15569E)
The circuit shown in the figure consists of an amplifier for stereo sources with Maxim's MAX9723...
Microphone Booster (CB923E)
This circuit was obtained in a 1980 edition of Elementary Electronics a magazine that no longer...