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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Relaxation with Operational Amplifier (CB25325E)
The figure shows the basic circuit of a relaxation oscillator with operational amplifier. The...
Voltage Range Detector (CB6672E)
This circuit was obtained from American documentation from 1966. It triggers when the two input...
Invisible rifle pulse LASER (CB6372E)
Found in an American 1980s documentation, this circuit generates high-intensity pulses for a...