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 circuit was found in an American magazine 73 for radio amateurs of the 80s. It is an...
Found in American documentation from the 1980s, this circuit can be designed with equivalent...
This circuit is from a 1977 documentation. It is powered by the power supply of the circuit under...