This circuit was found I a 1965 Radio Schack documentation. The transistors are from that time, admitting equivalents. The transformer has 500 ohm primary and secondary depending on the speaker.
We found this circuit in a 1967 documentation. The integrated circuit and an operational one of...
This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the...
This is the receiver for the previous circuit transmitter. Similarly, no information about the...