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 old Electronic Design. It makes use of sidacs and operational not very...
Although it was found in a British magazine 1976, this circuit can be easily upgraded with the...
This circuit that uses only transistors that are still common was found in a 1995 documentation. The TIP41...