Preamplifier stage (CB8934E)

This circuit is from a 90s Popular Electronics. It appears elsewhere on this site. Q1 can be any general purpose transistor.

Timed Code Switch Alarm (CB18003E)
Disabling this circuit from a 2002 documentation can only be done by pressing 4 keys in a correct...
JFET Timer (CB12123E)
This circuit was found in a 1979 magazine. We can use any JFET like MPF102 or BF245. The relay is 12 V...
Gain 1000 Amplifier (CB8998E)
This circuit was obtained in a 90’s documentation. The operational amplifiers are from that time....