This 555-based circuit was found in the August 1976 issue of Radio Electronics magazine. The tone frequencies are provided by the capacitors connected to the 555 IC.
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...