This circuit was found in old American documentation. It has 40 dB gain between 10 Hz and 10 kHz. Modern equivalent transistors can be used.
In the 110 V network, capacitors of 200 V or more and in the 220 V network, capacitors of 400 V or...
This circuit makes use of older operational amplifiers, but can be designed on the basis of modern...
This 12 V incandescent lamp switch with time delay can be found in old documentation. The SCR can...