Microtubes, November 1947 Radio-Craft

A month before Bell Laboratories' announcement of the transistor invention by Mssrs. Bardeen, Shockley and Brattain, Radio-Craft magazine editor Hugo Gernsback published a piece extolling the virtues of a newly developed microtube, aka a "rice-grain" tube. As connected as Gernsback was in the electronics industry, it is doubtful he knew of the impending game-changing invention. Commercialization of the transistor took a few years to get to the point where the devices could be manufactured cheaply and reliably enough to begin being integrated (pun intended) into products, so vacuum tubes still reigned for another decade or more. While the microtubes were designed into such products as portable radios, hearing aids, and other things in desperate need of size reduction, standard tubes continued to be used in the majority of things. Even the military and aerospace industries elected largely to pass on microtubes and instead wait for semiconductors. Still, there was no guarantee in 1947 that solid state would ever displace vacuum tubes for anything other than specialty products; it was still a very much unknown realm. Gernsback quickly embraced transistors after the announcement was made.

The above illustration is a considerably enlarged view of the National Bureau of Standard's new Microtube. At the right are rice grains, at the left a bookmatch for comparative size.

The Tube Laboratory of the National Bureau of Standards has just announced a new "rice-grain" radio tube - now known as the microtube.

This new subminiature radio tube is only slightly larger than a rice grain and only a bit wider than a book match, illustrated on this page. This constitutes possibly one of the greatest electronic developments in a decade. It certainly is a milestone in radio from every point of view. The development is so revolutionary that at this time it is impossible to foresee just how far it may lead us into further radio progress.

Complete technical details of the new tube cannot be given at this time because the new microtube has important military applications that can-not be revealed at present.

One of the important contributions which the National Bureau of Standards has made is in the reduction of microphonic noises and internal tube noises. As every radio technician knows, microphonics has been one of the great irritants in radio work and the Tube Division of the National Bureau of Standards is to be congratulated on this accomplishment, which ranks in importance with the reduction of tube size itself.

The Bureau mentions that these tubes will create profound effects in industrial and commercial fields, such as, for instance, in electronic computing machines. Present-day models of such machines use as many as 18,000 tubes in a single machine and some of the newer present models as well as others now being projected require as many as 2,000 radio tubes. It can be seen that by using microtubes a tremendous amount of space will be saved. This is true also in every type of radio where saving of space is an important factor.

While at this time of writing the tubes are not available commercially, they are now being developed by a large tube manufacturer who is working under a development contract.

Other important future projections of the new microtube can be readily made now that the new subminiature tube is a reality.

General David Sarnoff in 1921 predicted the eventual use of a wrist-watch size radio. General Sarnoff was serious when he made his prognostication, which now moves into the status of a distinct possibility. Indeed, a 5- or more tube superheterodyne watch size radio receiver now can be built with these new microtubes. There is no problem today as to the rest of the components which can easily go into a space the size of a man's wrist watch. The only thing that might baffle a constructor would be the batteries. However, this need not worry us too much either, because we can immediately think of a battery substitute.

Remember, these tubes do not use much current; therefore, we can imagine a miniature electric generator, powered by a watch-spring motor, using the recently perfected, most powerful Alnico V magnet. Such a subminiature generator becomes a distinct possibility. You merely wind the watch in the ordinary manner and the generator will keep running for a short period. It then can be rewound for more power. Thus, we will have a self-contained radio receiver compressed into the size of an ordinary watch. The face that normally is the crystal now becomes the loudspeaker diaphragm or cone, then by holding the wrist radio to the ear we should have clear and sufficiently loud reproduction to enjoy whatever program we wish to listen to.

Much smaller radios than these can be envisaged also for military purposes, such as subminiature radars, proximity fuses, handle-talkies, and a host of others. It has been said that World War II was won chiefly through the instrumentality of radio and electronics. The submarine war could not have been won if it had not been for our superiority in radar and associated other electronic techniques. Instant communication was a most important factor in winning the war. Radar for tracking down enemy aircraft was THE reason that made possible the aerial victory in the Battle of Britain. Without it there would not have been enough airplanes at the right spot at the right time, and the Battle of Britain certainly would have been lost.

If another war should come, we may rest assured that again radio and electronics will be the outstanding factor. Controlled missiles, in the so-called push-button war, could not be possible without radio-electronics.

The guided missiles now being perfected to protect our shores and to intercept other missiles will all contain the new microtubes. Indeed, the guided missile that can be followed from headquarters by means of television becomes now a distinct possibility due to the microtube.

For the pocket radio set, which has been in the developmental stage for several years now, the microtube will also become the most important factor due mainly to the great saving of space that can be achieved even over the present-day miniature tubes, still far too big, as we have pointed out a number of times.

There may also come a complete revolution in our radio receiver techniques. Some years ago we used to manufacture a radio tube that had all the elements of three tubes contained in one glass envelope. This tube proved too expensive to manufacture and is no longer made. But with the new microtube, an entirely new possibility, which the writer advances now, seems economically sound and feasible.

Instead of using five separate tubes in a superheterodyne receiver, five separate microtubes could all be placed into one envelope much smaller than the present-day standard tube. The new tube unit would merely have extending from the base the usual tube prongs, and instead of having five tubes we would have only one. This new multiplex tube therefore would be five tubes in one.

It would save an enormous amount of space in every radio set and it still would be cheaper than separate tubes. The wiring would become much simpler, the connections shorter, the weight less, and the cost would be reduced.

Then, if one of the multiple microtube units fails, the entire multitube simply would be discarded and a new one plugged in. It would save the service-man an enormous amount of servicing time if all radio sets would adopt such a multiple tube.

In this discussion we have merely scratched the surface of this new epoch-making development. In the next few years the microtube can be counted on to revolutionize many branches of radio and electronics, television not excepted.

Microtubes - A New Milestone in Electronic Developments November 1947 Radio-Craft

Microtubes - A New Milestone in Electronic Developments
November 1947 Radio-Craft