Frederick B. Llewellyn

Sixty years ago this month the PROCEEDINGS OF THE INSTITUTE OF RADIO ENGINEERS (IRE) included a paper by Frederick B. Llewellyn concerning the theory of vacuum tubes at ultrahigh frequencies. At the time he was employed as a research engineer at the Bell Telephone Laboratories. He began the paper by reviewing the history of the analytical theory of vacuum tubes at lower frequencies. He stated that designers of electronic circuits had relied on “cut and try” methods until the introduction of the theory of equivalent circuits by van der Bijl and others who showed that, for purposes of analysis, a vacuum-tube amplifier could be treated as a fictitious generator with an internal impedance determined from the static volt-ampere characteristics. Llewellyn continued that the key to the success of this method was in the separation of alternating and direct current components, with the equivalent circuit applying only to alternating currents. Continue reading