Integrator with JFET (CB6229E)

This circuit was found in an 80s National Semiconductor documentation. The configuration holds true for modern JFETs.

Resistance to voltage converter (CB9597E)
This circuit allows you to read resistors up to 20 M ohms, converting it into voltage. The circuit is...
Telephone dialer extension (CB9299E)
Found in a Hands-On Electronics from the 90s, this circuit produces the dial tones of an old...
Field strength meter (CB7358E)
This tuned circuit was found in a 1966 Electronic Circuit Handbook. The transistor can be any...