Grid leak detector (T415E)

This circuit was found in a modern documentation of experiments with tubes. It shows a typical AM detector used in many old radios.

Ultrasonic Oscillator (NI008E)
The 50 kHz signal generated by this circuit is applied to a low impedance inductive transducer. A...
Amplifier with the 4049 (CB4770E)
This different audio amplifier was found in a 90's Electronic Design. The circuit uses components...
Analog-to-Digital Converter – 555 (NI024E)
This circuit converts a resistance in the range between 1 k ohm and 1 MΩ to a signal in a...