This type of answering machine was common at the time this circuit was published. Using two tape recorders, it was published in the June 1986 issue of Radio Electronics magazine.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...