This circuit has the intensity of the signals controlled by the light that falls on the sensor. Note that it is not a frequency-controlled oscillator. Equivalent transistors can be used.
We can obtain the characteristics of an operational amplifier with FET by adding FETs common to the...
We found this circuit in an old English documentation. The JFET can be any general purpose and the...
This circuit is from 1995 documentation, with Q1 and Q2 of type 2N2218 or higher power. L1 has 3 + 3...