I found tis circuit in na old documentation from 1958. The circuit uses germanium transistor availble that time and hard to obtain today. The circuit is indicated for phono applications using variable reluctance transducer.
This circuit triples the frequency of a low-intensity signal and is suitable for VHF and UHF...
November 2016 - Maxim's MAX30003, an Analog Front End (AFE) for biopotentials with clinical grade...
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...