We found this circuit in a 1971 documentation. The circuit can be assembled with more modern transistors such as BC548 for Q1, BC558 for Q2 and BD135 for Q3.
This circuit was found in the August 1970 issue of Radio Electronics magazine. It employs RCA's...
This circuit is from 1968 General Electric documentation. It can certainly be adapted for any...
This tachometer from a 1994 publication has a bargraph scale with the well-known LM3914 integrated...