This circuit of an old medical publication makes use of an integrated circuit of the time, uncommon in our times. The sensors are diodes.
This circuit uses two Raytheon RC4558 operational amplifiers that are similar to the 741. The...
In the figure we have the way to obtain 500 gain from a FET. FETs can be BF245 or MPF102. The...
This circuit generates an FM signal of 4.7 or 10.7 MHz for audio signals on analog TV or FM, with...