This circuit was found in a 1967 Electronics World. We can design it with a BF245 for the FET and a BC558 for the bipolar transistor. The circuit has 3 scales and a 10 M ohm input resistance.
In the figure we have the way to use an operational amplifier on a higher voltage source than it...
This configuration is from a 1964 US documentation valid for any FET. The range of power voltages...
This circuit uses na Unijunction Transistor (UJT) to produce a modulation tone for several...