We found this version of the automotive tachometer in a 1980s publication. Variations from other sources appear elsewhere in this section. The indicator is a 0 to 1 mA milliammeter.
This circuit is from 1995 documentation, with Q1 and Q2 of type 2N2218 or higher power. L1 has 3 + 3...
This circuit was found in a 1965 Radio Shack documentation. The transistors are from that time....
This instrumentation circuit was found in the September 1989 issue of Radio Electronics magazine....