This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio Electronics from May 1963. The indication is by an analog instrument.
The operational amplifier can be of any type in this circuit, found in a 1974 publication. The...
This frequency divider with SUS was found in General Electric's 1967 documentation. Similar...
This adding amplifier with the operational LM324 is from the SGS integrated circuits manual of...