Low battery indicator (CB9133E)

This circuit was found in Maxim's documentation from the 80's. The integrated circuit is from that time, uncommon today.

2-Transistor Amplifier (CB22508S)
This 1950's circuit used one of the first commercial transistors and had two stages for audio...
Audio compressor (CB22154E)
Using integrated circuits from the time, we found this audio compressor in an English publication from...
Micro Radio (CB18167E)
This is an experimental crystal radio that uses no power source. The antenna must be very long (at...