This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646 and the coupler admits equivalent. The circuit is from a 1974 publication.
This operational amplifier configuration has gain controlled by an external voltage applied to a...
This circuit is from a Popular Electronics from July 1990. The magazine no longer exists, but the...
We found this 4.5 MHz amplifier for video signals from old analog TVs in the June 1992 issue of...