Serial switch with PIN diode (CB21257E)

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

Low battery indicator (CB9552E)
This circuit was found in a 90s American documentation from the 90s. The components are from that...
Clamp AC Microammeter (CB23563E)
In the figure we have the circuit of a clamp-type microammeter described in the Radio Electronics...
Gain 10 Amplifier – 741 (CB254E)
The voltage-gain for this amplifier is 10. Other operational amplifiers can be use and the Power...