Two-tube regenerative receiver (T1595E)

This circuit is from a Radio Electronics from 1949. The circuit is battery powered and has high impedance listening.

Adafruit Breakout PDM Microphone
Adafruit Breakout PDM Microphone This Adafruit tested microphone card is available from Mouser...
Mini Organ or Music Box (CB13836E)
This circuit was obtained in a Radio Shack documentation from 1977. The circuit generates a...
100 kHz Calibrator (CB3923E)
This simple calibration circuit consists of a crystal oscillator that generates an accurate 100 kHz...