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.
Found in ancient American documentation, this circuit uses some components from the time, such as...
In the figure we have the way to compensate an operational amplifier. The circuit is valid for...
With this circuit, it is possible to excite a white LED or another type of high brightness with...