Serial switch with PIN diode (CB21257E)

This circuit was found in a Popular Electronics from the 90's. The circuit is connected in series.

Simple Transistor Tester I (CB18917E)
We found this simple transistor tester in a French publication in 1981. It uses a common analog...
Speed Game (CB22072E)
Who is faster? or reaction game are other names for this circuit that we find in old...
Photodiode Amplifier (CB4950E)
This circuit is from an 80's component manual. The components are from the time, but the circuit...