Thermionic valves: a brief introduction

With the rebirth of thermionic valves (electron tubes) in audio amplifiers (note that they never 'died' in radio transmitters), it was feit that some (older) readers would appreciate a nostalgie reminder of what valves were like, Younger readers, not acquainted with valves at all (or very little) will, no doubt, be interested in what those funny glass (or metal) tubes are all about. Thermionic valves for use in audio circuits comprise diodes, triodes, tetrodes, beam tetrodes, and pentodes.