This 1969 circuit uses a 117 V filament tube powered directly by the power grid. The original circuit makes use of a charcoal microphone, a common component at the time.
The frequency of this oscillator can be set in a range from 5000 to 1. We found it in an old...
This filter was found in Radio Electronics, and its configuration can be applied to any...
The keyboard for this organ is made by small metal plates where the probe touches when in...