This telephone recording circuit was found in the June 1979 issue of Radio Electronics magazine. The components are common at the time and the power is supplied by the power grid.
This circuit, from a 1973 documentation, can be made with BC549 transistors. The frequency depends on...
The transistors in this 80's documentation project may be BC548, the most modern equivalents of...
This circuit was described in an article in the February 1993 Radio Electronics magazine. The...