Russ Wineno, WGAVG
The tubes illustrated here are known as the McCullough Kellog AC tubes. These tubes were originally designed to be able to use common AC house current (stepped down) without a great deal of hum, which was always present when an attempt was made to use AC on the filaments of the existing tubes of that day. These tubes employed an indirectly heated cathode rather than the plain filaments, and were a major break-through in the reduction of hum. First introduced in 1926 by McCullough, he soon sold out to the Kellog Switchboard Co. who continued to make them for some time, until RCA got into the act. Others followed Kellog, such as National Union, Sonatron and several other odd-balls which were no doubt adaptations of the RCA 227, to provide heater connections at the top and a four prong base for replacement purposes in radios built for the Kellog tubes.
Popular Radio Magazine of July-Aug. 1927, describes the McCullough AC401 as the pioneer among the AC operated valves. It is described as having the standard base of four prongs, only three of which are used and is suitable for any usage, to which the standard 201A can be applied. The same article also describes another AC tube called the "Sovereign." The characteristics are essentially the same as the McCullough, but the appearance differs slightly, in that the sides of the glass envelope are straight, and the heater terminals at the top are threaded and use knurled nuts.
Radio News for March 1929, lists tubes, among which are what they call the "Overhead Filament Types." They list the 401 with filament (heater) voltage of 3 volts, and current of 1 ampere, used as a detector amplifier (not power amplifier). Also listed is the 403 with filament (heater) voltage of 3 volts, and current of 1.5 amperes, to be used as a power amplifier. Incidentally, the 403 has straight up and down sides and is slightly larger than the 401. In 1928, a patent was issued to Earl L. Koch for a tube essentially the same as the McCullough, except for an additional grid element, which as supposed to assist in reducing the hum. This idea was abandoned and as far as I know, none were ever made for commercial use.
Copyright 1978 California Historical Radio Society, all rights reserved.
No part of this publication may be reproduced in any form, or by any means, without prior written permission from CHRS, except that you may make "fair use" of quotations of text fully attributed by you to the source (CHRS Journal) and author.
CHRS
PO Box 31659
San Francisco, CA 94131