This simple low power triplicator was found in 90’s American documentation. The diodes can be general purpose types and the frequency is determined by the RC network of the 555.
This simple electroscope with bipolar transistors is not the most sensitive, but can detect static...
This oscillator for various frequencies was obtained from a 1980s telecom documentation. The...
This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V...