This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
We found this 4W transmitter in a Mullard transistor manual from 1960. The circuit is powered by...
This circuit was found in a 1977 Radio Handbook. The MOSFET supports an equivalent. Capacitor C must...
This simple alarm was found in a 1982 documentation, but uses components that are still common,...