Pre selector (T435E)

This circuit was found in a 1938 Radio Handbook. The source is not given and the table for the coils is next to the diagram. The tube is an 1851.

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...