This receiver was found in a Popular Electronics from the 90's. Its different configuration shows a tuning circuit after the tube that works as an aperiodic amplifier. Observe supply voltages.
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...