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.
This circuit, found in a 1994 publication, allows the use of two common analog telephone sets on a...
This 1967 General Electric circuit makes use of an array of 3 (integrated) transistors for an...
This modulator circuit for low intensity signals is from old documentation. The integrated circuit...