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 filter with the 741 op amp was found in the February 1995 Electronics Now magazine. The power...
Suggested by an old American documentation the circuit below keeps a battery charged and at the...
Found in documentation from the 90s, this circuit was used in communications receivers of the...