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 circuit was found in a Popular Electronics from the 90s. The circuit uses a ceramic capsule as...
This circuit for link or alarm was found in the Encyclopedia of Electronic Circuits Volume 5 of...
This 15 W power stage was found in Radio Electronics magazine from August 1959. The transistors are the...