This amplifier was found in a tube equipment manual from 1947. The high-fidelity circuit has pentode tubes at the output and a source with transformer.
We found this logic level indicator in a 1976 amateur radio documentation. The circuit is powered by...
This circuit can be powered by voltages from 3 to 9 V providing output power from 100 mW to 1 W....
This astable multivibrator oscillates at a frequency of 1 kHz given by the capacitors and the base...