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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Continuity Tester (CB16894E)
We found this simple continuity tester in a 1995 documentation. It uses two LEDs to indicate...
Operational Triangular Oscillator (CB14081E)
We found this oscillator in the 1994 National Semiconductor Handbook of Linear Applications. The...
Temperature controller 555 and triac (CB9470E)
This circuit was found in a 90s Electronic Design. The circuit directly controls a triac that is...