We found this circuit in the Linear Applications Handbook by National Semiconductor. It uses the LM3900, an operational transconductance amplifier as a base. Q1 can be a 2N2222 or similar.
On this 1960s circuit, stations are pre-tuned in trimmers and then selected by a switch. The...
This small shaver bender circuit makes it possible to use 220/240 V shavers on 110 V networks. The...
The operational amplifier used in this application is not the most common today. The circuit is...