This circuit was found in a 1924 Gernsback publication. The variable capacitors are dual. Listening is through a high-impedance phone.
The figure shows how to convert a rectangular signal into a triangular signal using an integrator. The...
The HA2620 integrated circuit used in this comparator is from the 80's, but the setting can be...
This circuit is from a very old publication, from the 60s. It uses germanium transistors from the...