This circuit was found in a Philips documentation from 1967. The circuit uses components from the time that have current equivalents such as BC548 for transistors.
This instrument was found in a publication for radio amateurs in 1973. The tuned circuit consists of...
This transistorized astable for LEDs was found in the January 1992 issue of Radio Electronics...
This circuit was found in a 1977 Radio Shack documentation. The circuit is tuned to 1.4 kHz, but...