Logic level indicator 7400 (CB22407E)

In the figure we have a simple logic level indicator for TTL circuits or powered by 5 V.

Two-band loop antenna (CB6979E)
Found in Popular Electronics from the 1980s, this circuit can use more modern transistors such as...
Mixer CA3035 (CB23997E)
This circuit is from a Radio Electronics from February 1970. The integrated circuit is an...
Transformer Amplifier Stage (CB966E)
This is stage is transformer coupled and was found in na old publication of the year 1958. The...