This battery-powered 3-valve circuit was found in American documentation from 1947; Two batteries are used, one high voltage and one low voltage for the filaments.
This is a multi-component tester with visual indication by LED and polarity selection in the test....
This circuit is from a 1978 operational amplifier manual. The power supply must be symmetrical, and the...
This circuit is stabilized by a thermistor or NTC with a resistance between 2 and 5k. The signal is...