This is the receiver for the previous circuit, also found in 90s Radio Electronics. The circuit operates at 2.25 MHz, detecting variations in signal frequency due to the Doppler effect.
This experimental amplifier was found in the 1960 Mullard transistor reference manual. The...
This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit...
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...