This transistorized circuit appeared in a Radio Electronics magazine in March 1958. The frequency range depends on the tuned circuit, being within a few megahertz.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...