| The indicator shows when the mains is present at its output by a continuous glow of a neon bulb, La1, and when the fuse is blown by flashi...
| The indicator shows when the mains is present at its output by a continuous glow of a neon bulb, La1, and when the fuse is blown by flashi...
| An amplifier is described which, after a tuning fork has been struck, gives a continuous 440 Hz tone (= International A), so that the user...