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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Night Switch (CB491)
This circuit turns on a lamp when the night comes and turn it off in the morning. The circuit...
Balanced Microphone Preamplifier I (CB4943E)
This circuit was obtained from an American publication of the 80's. The integrated circuit is of the...
Operational Flip Flop (CB4839E)
In the figure we have a traditional flip-flop configuration implemented with two operational...