Using junction FETs, a configurable configuration is achieved for very low frequencies. FETs can be of almost any type and the frequency depends on the capacitors.
This circuit was obtained in a 1977 magazine, but it can still be easily assembled, as the...
This intercom for the 27 MHz band was found in a recent English documentation, working with a...
This relay shield circuit for old computers was found in January 1983 Radio Electronics magazine. The...