If you ever look at construction notes for building old detector type radios the type of headphones specified always have an impedance of 2 × 2000Ω. Nowadays the most commonly available headphones ...

I am just finishing a new transmitter facility at the Empire State Building and there were a couple of times that I needed power supplies to keep various relays energized (like remote interlocks) or ...

A diode is a semiconductor device that allows electrical current to flow in one direction while blocking it in the other.