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.
This is the circuit of a digital clock published in the January 1975 issue of Radio Electronics magazine....
This output stage can directly excite a small speaker. The circuit is from a 1960 Mullard...
In the figure we have one of the many options found in this section for an intercom using ordinary...