Discussion of "A History of Some Foundations of Modern Radio-Electronics Technology" Page 1255

1) Initial interest in the possibility of some form of vacuum tube amplifier, aroused through contact with Peter Cooper-Hewitt’s mercury arc rectifier tube (a form of which Hewitt himself was developing as an amplifier).

2) Familiarity with the Audion grid detector, gained while working as a consultant for de Forest’s old Radio Telephone Company, soon defaulted, 1909–1910, which led Fritz to try to make of the audion an audio-frequency amplifier. He seems to have had some success, but evidently kept it to himself at the time; his obligation to the Company is not known.

3) Renewal of the audion amplifier tests in the fall of 1911 with Hammond’s backing, resulting in amplified reception of long-distance telephone calls and in the attainment of a true Class A amplifier by means of the negative grid discovery.

Therefore, it is seen that Lowenstein was on the trail of the audion amplifier before becoming associated with Hammond and carrying out the “further work on the invention in the way of perfecting the details thereof.” Under these circumstances the paper is misleading in implying that he started the development on May 11, 1911 and in the capacity of consultant to the Hammond Laboratory.

The Oscillating Audion

It is well established, as the authors say, that Lowenstein had the audion amplifier working as an oscillator toward the end of 1911, and for both audio and radio frequencies. The strange thing is that it was not followed up, the more so in view of Hammond’s high hopes for it as expressed in his letter to Beach Thompson of January 25, 1912, given below. And it is singular that to Hammond, “The exact nature of the ionic devices and the manner of operation are not known.” One wonders too that the evidence of Lowenstein’s having the audion as an oscillation generator during the winter of 1911–1912 was not presented to the courts in the long de Forest-Armstrong litigation over the oscillating tube. Such evidence would have demonstrated the natural tendency of an amplifier to oscillate and hence how little invention there was in the oscillating audion per se once it had become an amplifier. As matters were allowed to go, it fell to others to give to the world the oscillating audion in useful form, most notably, perhaps in terms of early date and application of control of frequency, to Alexander Meissner of Telefunken¹⁶ using a gaseous tube of the von Lieben Triode.

An Important Tip

In view of its probable importance for de Forest, then working at Palo Alto, Calif., for the Federal Telegraph Company, the letter which Hammond wrote the President of that company, and from which the Hammond-Purington paper quotes in part, deserves to appear in full:

January 25, 1911.
(Typist’s error, should be 1912)
Beach Thompson, Esq.,
President, Federal Telegraph Co.,
Merchants Exchange Building,
San Francisco, California.

Dear Sir:

I have recently been informed about the wireless work you have been doing on the Pacific Coast, and I am much interested in the results that you have obtained. If you have any descriptive matter I would appreciate your sending it to me.

I have been experimenting with a new form of apparatus designed to produce undamped and high frequency oscillations. Our method is far more reliable and simpler than the Poulsen arc method, or the high frequency alternator system as used by Fessenden and others. We are in process of developing this apparatus, and when it has reached a practical point, I would be very glad to send you more complete information regarding it.

In the experiments we have found that our method is highly suitable for wireless telephony, as there is absolutely no sound produced whatsoever as in the arc or hf alternator. I believe that telegraphy by means of undamped high frequency oscillations is the logical future of this art, for the reasons which you have already discovered and proven: that far better tuning may be obtained where there is no decrement to the wave train, and that there is less absorption of energy in long distance transmission, and also the important fact that low voltages are used at the transmitting station. However, the chief weakness in all systems of this kind is essentially in the means of producing the continuous high frequency oscillations.

I am quite familiar with the art in Europe and during my recent trip to Germany found that most of the companies had abandoned the arc method of oscillation production. It is for this reason that I believe there is quite a future in the development of the work which we are carrying on.

Hoping that you will be kind enough to send me any data which you may be willing to disclose, believe me

Yours very truly,
JIIIJr/T

On the same day Hammond wrote to an acquaintance of Thompson, and since this letter, too, is evidence of a stimulative tip given the Pacific Coast people, it is presented:

January 25, 1912
Major F. R. Burnham
Llankershim Building
Los Angeles, California.

Dear Major:

I want to thank you very much for your letter in regard to wireless development in California. It certainly is very interesting to me as the reports I have had of this enterprise have been very meagre. I will herewith write Beach Thompson, informing him that the iron controller which you saw in my experimental laboratory here has recently shown some remarkable results in experiments in which we produced high frequency undamped oscillations with far better results than have ever been obtained by the Poulsen method.

I hope some day that I will be able to introduce a wireless system in Sonora. After the Yaqui has developed enough they will need a station there, and we could furnish a good one.

Very sincerely yours,
JIIIIJr/T

(The term “iron controller” is a stenographic slip for “ion controller.”)

Photo copy of each of the above letters (from Hammond’s file carbon copy) were kindly given the present writer some years back by Hammond and Purington. Appreciating the probable bearing of them upon de Forest’s making the audion into an amplifier at Palo Alto in the summer of 1912, a copy of the letters was sent to him, with the question of whether they may not account for Beach Thompson having asked him to undertake the further development of his audion. Dr. de Forest’s response was: “I do not recall that Beach Thompson ever mentioned his correspondence with Hammond, but very likely that is what induced Thompson to urge me to develop the audion as an amplifier.”¹⁷ Whereby we see that Lowenstein, having been indebted to de Forest in the first place for the vital grid tube, repaid his obligation through Hammond’s letter, perhaps unwittingly!

Bell System Side of the Picture

An insight into what was happening within the Bell System at the time of the Hammond-Lowenstein approach may be welcome: the American Telephone and Telegraph Company and associated Western Electric Company already had started tackling the telephone repeater problem from the standpoint of a vacuum tube element of some kind. From the University of Chicago laboratory of Prof. Robert A. Millikan a young graduate student, Dr. H. D. Arnold, had been recruited. He started to work at the beginning of 1911 and took up the kind of vacuum tube that seemed likely to carry the load of a telephone repeater, the mercury-arc tube similar to that of Peter Cooper-Hewitt. He had succeeded in getting amplification when our present story opens.

On January 27, 1912, Hammond and Lowenstein took to the office of transmission engineer F. B. Jewett a sealed box and demonstrated it as a prospective telephone repeater. Further contact was made in June, and there were additional telephone conversations, but not until January 12, 1913, while Lowenstein was in Europe, was it fully disclosed what was in the “Black Box.”

Meanwhile de Forest himself had succeeded in making his audion into an amplifier on the Pacific Coast, in the summer of 1912, and through John Stone-Stone approached the American Telephone and Telegraph Company. De Forest came east and on October 30 and 31 demonstrated the audion as an audio amplifier to Dr. Jewett and E. H. Colpitts in the laboratory of the Western Electric Company, at 463 West St., New York. He left the device, and the following day, November 1, Colpitts called in Arnold and showed it to him. Arnold later testified frankly as to his impression: “. . . when I went into the room and saw this thing and saw how it worked I was very much astonished and somewhat chagrined because I had overlooked the wonderful possibilities of that third electrode operation, the grid operation in the audion. . . . I knew about the de Forest audion in print, but I was wrong in my impression of what the de Forest audion might do because I had not realized what the grid would do in such a device.”¹⁸

Thereupon Arnold turned from his own mercury arc tube to embrace the audion. As demonstrated by de Forest it was a remarkably sensitive but weak and unreliable amplifier. It would amplify only at low speech levels, about 30 db down; at normal levels it would block and produce noise, for the audion still had in it the grid condenser of its radio detecting days! This trouble was soon overcome and Arnold then addressed himself to the improvement of the tube itself. He had recognized from the beginning

¹⁶ A. Meissner, “The development of tube transmitters by the Telefunken Company.” Proc. IRE, vol. 10, pp. 3–23; February, 1922.
¹⁷ Letter to Dr. L. de Forest to L. Espenschied, September 15, 1953.
¹⁸ Arnold-Langmuir high-vacuum tube litigation. Testimony of 1926 in the District Court of the U. S., District of Delaware, No. 589 and 598. In Equity. General Electric Co., Plaintiff, vs The de Forest Radio Co., Defendant. Vol. I of six volumes, pp. 554–556.