Hearing aid amplifier (T1580E)

This circuit is from a 1947 Radio Electronics. The 4-tube circuit is battery powered and uses a crystal phone.

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Space Gun (CB20449E)
This circuit can be installed inside a toy space gun to produce a “Phaser” effect. The circuit is from...
Timed Residential Alarm (CB16558E)
This circuit was found in a 1988 publication. The circuit is an alarm with interrupt sensors that...
Relaxation oscillator Using Bipolar Transistors (CB884E)
The frequency in this circuit is adjusted by P1 and given by C1. Short pulses, as the ones...