This TTL time base for 60 Hz or 50 Hz can be used in instrumentation circuits or even with microcontrollers, serving as a precision shield. The circuit is based on 7400 NAND ports and two transistors.
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
This filter was found in Texas Instruments documentation from the 1980s. The circuit uses a common...
16 commercial test circuit for tubes and transistors appeared in Radio Electronics magazine in...