Oral-History:Herbert Doring

About Herbert Döring

Herbert Döring

Herbert Döring is a communications engineer best known for his work in electron tubes. He received his diploma in electrical engineering from the Technische Hochschule Vienna in 1934, and received his Doctor Techn. in electrical engineering from the same university in 1936. He worked at Siemens in Vienna and then at the AEG Institute, moving to C. Lorenz AG in 1941 as Oscar Heil's successor. He became a professor at Aachen in 1952 and founded the Institute of High Frequency Technique there in 1957. He retired in 1980 and has spent his time since publishing on the history of electron tubes and on new systems of electron tubes.

The interview begins with Doring's education in Vienna, where his doctoral work was on transit time effects in diodes. He then discusses his work on receivers at Siemens and at AEG, just after the Anschluss. He discusses his work at AEG under Prof. Ramsauer on electron transit time effects and on centimeter generators for radar; some of his wartime work was secret. He describes his work on klystron oscillators at C. Lorenz and the effect World War II had on Lorenz and on Döring's work. He comments on Americans who came after the war to examine German developments, and notes the technology transfer between American and German industry at that time. He discusses his role in the planning of the Institute of High Frequency Technique and the differences between his industrial work and his academic work. He discusses his own and others' publications in the history of electron tubes and on new systems. He outlines major developments in the history of electron tubes, and describes how his reading and translating work furthered his education in electron tubes. The interview ends with Döring mentioning his interest in the reflex klystron and assessing Gerald Tine's Saga of the Vacuum Tube.

About the Interview

HERBERT DÖRING: An Interview Conducted by Frederik Nebeker, Center for the History of Electrical Engineering, 1 September 1994

Interview #233 for the Center for the History of Electrical Engineering, The Institute of Electrical and Electronics Engineers, Inc.

Copyright Statement

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It is recommended that this oral history be cited as follows:

Herbert Döring, an oral history conducted in 1994 by Frederik Nebeker, IEEE History Center, Hoboken, NJ, USA.

Interview

INTERVIEW: Herbert Döring

INTERVIEWER: Frederik Nebeker

DATE: 1 September 1994

PLACE: Aachen, Germany

Family Background and Education

Nebeker:

I'm with Herbert Döring. This is Rik Nebeker. You were born in 1911, in Vienna?

Döring:

Yes, Austria.

Nebeker:

And you did your schooling in Vienna?

Döring:

Yes.

Nebeker:

Can you remember the First World War?

Döring:

A little.

Nebeker:

You were very small.

Döring:

There was not much to eat, and my father was working in the Austrian-Hungarian Bank. Therefore he did not have to go into the military. He stayed at home. I remember my mother had made him a chain to stay at home.

Nebeker:

Yes, I've heard how difficult it was near the end of the war and right after the war in Vienna.

Döring:

For me it was only having not much to eat. I had no other difficulties.

Nebeker:

And you went to a gymnasium in Vienna.

Döring:

Yes, to a real gymnasium.

Nebeker:

Right.

Döring:

For eight years. Then I went to the Technische Hochschule in Vienna and studied electrical engineering. There was at that time only one course of electrical engineering, not divided into high frequencies or other areas.

Nebeker:

Right, I see.

Döring:

I studied more high-powered engineering than high frequency engineering.

Nebeker:

That was the standard sort of engineering I guess at the time. So you completed your studies there —

Döring:

1934. I made the diploma and two and a half years later the Doctor —

Nebeker:

Doctorate, yes.

Döring:

Yes. In Austria this is called Doctor Techn. Not Doctor Eng.

Nebeker:

Is it equivalent to Doctor Eng. in Germany?

Döring:

Absolutely equivalent. Then I was two years in industry at Siemens in Vienna, working on broadcast receivers.

Doctoral Work: Transit Time Effects

Nebeker:

Could I ask you about your doctoral work, what you did for that?

Döring:

I worked on transit time effects in diodes. It was 1935. We built in the institute small diodes, not with plane surfaces but wires only, and I made measurements at forty centimeters with an American acorn tube generator. You know acorn tubes?

Nebeker:

Yes, I've heard of them.

Döring:

Those are tubes with the pins positioned radially.

Nebeker:

Yeah. What were your diodes intended for?

Döring:

For detecting.

Nebeker:

So you worked on these diodes for your doctorate?

Döring:

I tried to measure and calculate the influence of high frequencies on the DC current.

Siemens: Broadcast Receivers

Nebeker:

I'm sorry; what did you tell me you did at Siemens those two years?

Döring:

Siemens, in Vienna. There I developed broadcast receivers.

Nebeker:

Broadcast receivers. I see.

Döring:

This was interesting in 1936. The so-called audi ngsuper [sp?]. That's a special super-regenerative receiver with only three tubes.

Nebeker:

I see.

Döring:

It was new at this time.

Nebeker:

Where was it designed? At Siemens?

Döring:

At Siemens. Yes. And Siemens in Austria was combined with Telefunken in Germany.

Nebeker:

I see.

Döring:

They were brother companies.

Nebeker:

Yes.

Döring:

And this super had only three tubes. One mixer and local oscillator (octode) tube at the beginning. Then an intermediate frequency amplifier tube and a detector and lf tube. The intermediate amplifier was made with an adjustable feedback.

Döring:

But the receiver was not fabricated. It was too difficult to find the right degree of feedback at deviations of the line voltage.

AEG and the Anchluss

Döring:

Then I went to the research institute of AEG, to Berlin. There was given in 1936, in Vienna a lecture of Professor Brüche of the AEG research institute, and I heard it. It was so interesting that I went to him and asked him whether I could come to the institute. In 1938 I received permission to come to Berlin as an Austrian, and to work on secret things. But in 1938 it was not necessary, as on the thirtieth of that March the two countries combined. The Anschluss.

Nebeker:

Right.

Döring:

On the day of the Anschluss, I received accidentally the invitation to come to Berlin.

Nebeker:

Is that right?

Döring:

Yes.

Advances in Broadcast Receivers

Nebeker:

Before we go on about this — I've heard that in the United States in the 1930s the principal development with broadcast receivers was trying to reduce the cost, to be able to manufacture them less expensively.

Döring:

Yes, the German popular receiver (Volks-empfinden). You can see it in the museum. There are two types. One type was for sixty-five DM, and the smaller was for thirty-five DM.

Nebeker:

I see.

Döring:

These were the people's receivers (VE and DKE).

Nebeker:

Right.

Döring:

The small one was called the German small receiver. (Kleinempfinden).

Nebeker:

When were they developed? Mid-1930s, somewhere?

Döring:

Perhaps 1933. The small one came perhaps a little later. This is perhaps interesting to you: The small one was called by the population, Goebbels’ Schnauzer. A "Schnauzer" is the name of the mouth of an animal.

Nebeker:

That was probably partly for Nazi propaganda purposes?

Döring:

Yes.

Nebeker:

So that everyone —

Döring:

Could hear local broadcasting.

Nebeker:

So you moved to Berlin in —

Döring:

1938.

Prewar Berlin

Nebeker:

How was the atmosphere there for you in Berlin just before the war?

Döring:

I worked in the institute with a number of good colleagues. One colleague was also a Jewish professor.

Nebeker:

Who was that?

Döring:

He has died now. He said one day to me, "Now, Döring, don't go and speak with me on the street. I am Jewish. That's bad. Perhaps bad for you." But he could work — he was a mathematician. You know the name perhaps: Richard Ganz.

Nebeker:

Ganz. He was in that same research institute?

Döring:

He was a professor at the University of Königsberg. And was now engaged at work on magnetic mines. I also had another colleague, an Austrian, whose name you will know. Professor Alexander Meissner.

Nebeker:

Right. Oh, yes.

Döring:

Meissner worked on receivers and transmitters in 1912, 1913.

Nebeker:

Right.

Döring:

Very early.

Nebeker:

Did it appear to you that war might be coming?

Döring:

We feared that war might be coming, but we hoped that it would not come, you know. In Berlin it was a very quiet life. A very safe life. One could take his bicycle and leave it before the house. Not locked. And nothing was stolen.

Nebeker:

I see.

Döring:

It was quiet.

Wartime Work at AEG and Lorenz

Nebeker:

What did you work on? What was your first project at AEG?

Döring:

I was told to work on electron transit time effects. My boss was Professor Ramsauer. Ramsauer was famous for the so-called Ramsauer Effect. He was the boss of the institute, and he came only one in the year for half an hour to see what we were making in the laboratory. And some days later he had to give a report for the board of directors. He told them in two minutes what I was making. I was not the only one; there were a lot of scientific colleagues. But he had the survey.

Nebeker:

Were you pleased that he told about your work?

Döring:

Yes.

Nebeker:

You were looking on transit —

Döring:

Yes. Transit time effects in electron tubes.

Nebeker:

What was the aim?

Döring:

In diodes, with plan electrodes at very high frequency not all emitted electrons to reach the anode. They return to the cathode and different effects occur.

Nebeker:

I see.

Döring:

And if you take f.e,. [?] an oscilloscope at high frequencies the electrons are deviated otherwise than at low frequencies. A colleague of mine, Dr Recknagel calculated the effects of deflection at high frequencies. He calculated that if the frequency and the voltages are so chosen that the time of transit through the deflection condenser is between 2 Pi or 2.5 Pi. This arrangement together with a parallel inductance is able to oscillate without an external oscillator.

Nebeker:

Yes.

Döring:

I could not realize the oscillations, but I could measure the mean velocity of electrons leaving the condensor at high frequencies. I found that if we are in the above named transit time range, there is a reduction of damp. I could see this measuring near the velocity of the electrons. It was an interesting effect. It is not used now, but at that time we tried to find cheap, small generators for centimeter waves.

Nebeker:

It did not work.

Döring:

Now we know exactly why it did not work, but at this time it was new.

Nebeker:

And the reason for wanting a centimeter generator was for radar purposes?

Döring:

For radar, yes.

Nebeker:

Did you know what it was to be used for?

Döring:

It was a secret. It was sometimes secret research. I had colleagues in other industries, and we were forbidden to speak. It was not good. In 1943 Professor Esau became the supervisor for high frequency problems in Germany. He was directly under Hitler. He was an old member of the Nazi Party. He was a very scientific man. He thought that we must speak together so we could relate all our problems.

Nebeker:

So he was appointed in order to get the radar research moving faster.

Döring:

Abraham Esau. Professor in Königsberg. But not Jewish.

Nebeker:

I see.

Döring:

Those biblical names are very seldom in Germany but often in East Prussia.

Nebeker:

Yes.

Döring:

Königsberg was in East Prussia.

Nebeker:

East Prussia, yes. I see. So you continued to work there until 1941.

Döring:

In 1941 I came to C. Lorenz, AG and I became the successor of Oscar Heil. Do you know the name?

Nebeker:

Yes.

Döring:

He died now some months ago. I received the telegram from his wife, but his wife is also ill. She had cancer. And I have written at the moment an obituary for Oscar Heil. I knew him well. He was at Lorenz before me and I continued his work. He was interested that his work went on. Therefore we had in the evening, when I left the firm, several long speeches at Berlin along the Spree River.

Nebeker:

How did you learn about that job? How was it just offered to you? Did Heil come to you and say he would like you to work there?

Döring:

The director of the Lovess Tube Laboratory wanted me to come. He knew that Heil would leave, and I was working on transit time effects. In Heil’s tube transit time effects are used. And I was known by my theoretical and experimental work of AEG.

Nebeker:

I see.

Döring:

He told me all and I told him all.

Nebeker:

And there was no problem at that time in changing jobs?

Döring:

It was difficult, but AEG was working for the Navy (and the Air Force was stronger than the Navy). Lorenz worked for the Air Force. I had six weeks between them. That was not normal in Germany at these times.

Nebeker:

And Lorenz is also in Berlin?

Döring:

Yes. Lorenz was working in Berlin.

Nebeker:

Yes.

Döring:

The Varians who invented the klystron did not know Heil’s paper. Heil’s paper was 1935. It was published at the same time as the klystron work began. The Varian paper was published in the Journal of Applied Physics. That we could receive in 1939. My colleague Ludwig Mayer and I were working on transit time effects and we read this paper. Very excitedly we translated it into German and made abstracts for German newspapers. Therefore we knew it very well, and we began to work on a klystron oscillator. Mayer was working for the dealed off tube, [?] not working on the pump. My construction was working on the pump. His construction was too difficult to realize.

Nebeker:

This was something you designed yourself? This klystron?

Döring:

It was my design and it had only one mechanic and nearly no microwave measuring technique. He was a good man. This Klystron delivers 100W at 30 cm. The AEG did not use this tube. They said, "That's very good." But Professor Ramsauer [sp?] was no Nazi — he was anti-Nazi and therefore he made no use of this work.

Nebeker:

He didn't want to develop it. I see. Did you continue that when you went to Lorenz?

Döring:

I continued Heil’s work a special Klystron oscillator and I stayed at Lorenz until 1952 when I left and went to RWTM AACHGN [?].

Nebeker:

How were the last years of the war for you when you were still in Berlin?

Döring:

I stayed in Berlin until January 1944. Then our firm was —

Nebeker:

Moved?

Döring:

Yes, moved to Neutschein. That's a little town in the mark [?] of Czechoslovakia.

Nebeker:

I see.

Döring:

A German-speaking town, but it was in Czechoslovakia.

Nebeker:

Yes.

Döring:

Near the Russian border. So it was not very good. But at this time in1944 the Russian forces were very distant and we built a tube factory there. When it was working the Russians came and we had to move again. We went to Auerbach in Saxonia, in Germany —

Nebeker:

Yes.

Postwar: Receiver Tubes

Döring:

Here he erected a new fabrication place. It was finished when the Americans occupied Auerbach and the war ended. I went by night three days to see my family, which was in Bavaria at this time, and the Russians came then to Saxonia, and I could not return. Lorenz sent all the things from my room to Bavaria. In Bavaria we tried to find a place to erect a new fabrication place for electron tubes, and it was in Esslingen in Württenberg. There I worked until 1952. I was with the first ten men who went to Esslingen. We were planning a new factory for receiver tubes. Only receiver tubes.

Nebeker:

Were you designing receiver tubes as well?

Döring:

Yes. At this time I made a combination tube of a triode, and a pentode. It was used for a special small receiver with only one tube, the above named DKE.

Nebeker:

Was this for military applications?

Döring:

No, for the population.

Nebeker:

Is this something that you had developed?

Döring:

Yes, the tube was fabricated in a large number of pieces. And the purpose here was to be able to make a radio with just a single receiving tube?

Döring:

Yes. Perhaps it is interesting for you: I built during the war, in 1943, a special velocity-modulated tube, the so-called RD12 LA. That was a transmitting tube, perhaps fifteen watts, tunable around twenty centimeters, for a telephone repeater.

Nebeker:

Oh, a portable repeater.

Döring:

Yes, used during the war from Berlin to the German troops in the Caucasus.

Nebeker:

I see. So this was a field telephone repeater.

Döring:

Yes, a telephone repeater.

Nebeker:

You designed that?

Döring:

I designed this tube. I can show it to you in our museum. Yes, a further development of the Heil tube; I made it tunable but between 18 and 50 cm.

Nebeker:

Okay.

Döring:

<flashmp3>233_-_doring_-_clip_1.mp3</flashmp3>

It was only a small oscillator tube. Lorenz was a part of General Electric in America before the war. After the war the people from General Electric came to us and wanted to see what we had made until then. I received the task to build one hundred of these tubes, but we could not build these tubes because we had not the necessary means, therefore we built in another place in Bavaria, near Munich. I had the task to go there to see that the tubes were built, and took the tubes in my backpack, and I took this to Lorenz. There we made some measurements and gave them to the Americans, but they were never used. They were destroyed afterwards. This was the only way that the people who were working on this subject could remain together, and not go to another firm. That was the reason for this order. For me it was very agreeable. It was an interesting work, and I could go by train from Esslingen to Munich. In Esslingen there was not much to eat. In Munich there was more to eat. But in Esslingen we had nails and tools. And I took the nails to Munich.

Nebeker:

They didn't have nails in Munich?

Döring:

No. I could exchange them for food!

Nebeker:

I see.

Döring:

And in Munich, at the station, there was a place where one could sell American cigarettes. I received American cigarettes from my American officer who was in the firm.

Nebeker:

I see.

Döring:

Each week one package. When I went to Munich I could sell it for a hundred marks. Yesterday I was in Munich, and I passed this place where I sold them.

Nebeker:

Oh, my goodness. So these were people from General Electric who came to Lorenz to find out about your work.

Döring:

Yes.

Nebeker:

Did military experts come to your group to learn about your work?

Döring:

Sometimes. Not only from General Electric, but also from other firms. Sometimes in uniform and sometimes without.

Nebeker:

I see. And there was a very large transfer of technology at that time?

Döring:

Yes.

Nebeker:

Military people were going to German companies.

Döring:

Shall I give you some papers in German? Is it of interest?

Nebeker:

Yes, very much.

Döring:

I will give you this tube paper. On this tube there was not much published, and therefore I have written the last time on this tube.

Traveling Wave Tube

Nebeker:

What work did you do besides this tube in these years after the war that you were still at Lorenz?

Döring:

Further I published papers on every theoretical work on efficiency calculation and on starting of oscillations in velocity modulated tubes. After the war I directed a small laboratory for measurements at high frequencies. Ten centimeters.

Nebeker:

Ten centimeters?

Döring:

Then I developed traveling wave tubes when I was allowed. The klystrons were not allowed at the beginning.

Nebeker:

Is that right?

Döring:

I had forgotten to say that. It was very forbidden to work on such things.

Nebeker:

I see.

Döring:

But I received from the Americans permission to continue work on the RD12 LA.

Nebeker:

What was your reason for working on these traveling wave tubes?

Döring:

Oh, worldwide it was a coming tube. It was an interesting coming tube.

Nebeker:

For what applications were —

Döring:

Applications? At these times it was the beginning of the satellite. The traveling wave tube was invented by Rudolf Kompfner.

Nebeker:

Right.

Döring:

I knew him also personally.

Nebeker:

Where did you know him?

Döring:

He studied in Vienna. He was also from Vienna, and he was a colleague of my brother, and he was a former architect. He was a Jewish refugee who went to Cambridge and changed from architecture to electric engineering.

Nebeker:

And I think later to the United States.

Döring:

Yes.

Nebeker:

I see. So it was mainly traveling wave tubes that you were working on?

Döring:

No, no. I was beginning in 1950, 1951 and the work was continued from Dr. Klein. He was my pupil at TU Stüttgart and my successor at Lorenz.

Institute of High Frequency Technique

Nebeker:

So that was in 1952 when you became professor in Aachen.

Döring:

Yes.

Nebeker:

It says you founded the Institute of High Frequency Technique here.

Döring:

Yes. There was nothing here. In 1957, I received a new institute, this building. I planned this institute with my neighbor, Professor Aschoff. He is a professor for electrical communication —

Nebeker:

Yes.

Döring:

But he is not working now. He is three years older than me.

Nebeker:

I see. How did you like that? Coming to a technical university? You had been in industry for quite a time.

Döring:

It was not my plan to come, totally. I wanted to do both fields close together. To stay in industry and to go one day, or one half day a week to the Technische Hochschule in Stüttgart and give my lectures on microwave tubes and on microwave measurements.

Nebeker:

I see. What research did you do?

Döring:

Here?

Nebeker:

Yes.

Döring:

I continued centimeter wave measurement technique. I was working on ferrites at higher frequencies. I was not working on electron tubes — it was not possible for such an institute. There must be pumping stations and small receiving tubes became unattractive.

Nebeker:

I see.

Döring:

Industry makes this better. But I continued to supervise electron tube development.

Nebeker:

What were the types of tubes that were in Germany being developed?

Döring:

For short waves and for high power.

Nebeker:

Oscillators?

Döring:

Oscillators and amplifiers.

Nebeker:

I see.

History of Electron Tubes

Döring:

I have been retired since 1980. Fourteen years. A long time. And I am now writing papers on two topics. First on the history of electron tubes. There are not many people living who know the development of electron tubes, especially in Germany, or in Europe. I write in this direction. Further I described new systems of electron tubes, like the gyrotron, the vircator, the magnicon, and so on. That's high power tubes in the megawatt range. These were developed in America and Russia some years before SDI, you know?

Nebeker:

Yes.

Döring:

And now they are used as high power generators for accelerators.

Nebeker:

I see.

Döring:

Particle accelerators.

Nebeker:

Particle accelerators. You were involved in the design of these tubes?

Döring:

No, no. I follow only the literature but a former student of mine is designing.

Nebeker:

I see; you're just studying them.

Döring:

I know how they work, but I could not make them.

Influential Books

Nebeker:

What books have been very important to you in the course of your career?

Döring:

What books?

Nebeker:

Yes, what books. Sometimes an engineer will say Terman's Radio Engineers Handbook, for example, was a very important book to them.

Döring:

I know this excellent book but I have not used it.

Nebeker:

What are the ones that are very important to you? Your career?

Döring:

Now, or formerly?

Nebeker:

Formerly.

Döring:

The four books of Barckhausen.

Nebeker:

Barckhausen?

Döring:

Barckhausen, yes. And the books of H. Rothe and W. Kleen.

Nebeker:

What book is that?

Döring:

That is also on electron tubes. Rothe-Kleen. They were modern engineers at Telefunken.

Nebeker:

When did that book come out? Do you know, roughly?

Döring:

1941-1949.

Nebeker:

1941. That's Electron Tubes as Oscillators and Rectifiers.

Döring:

As oscillators and rectifiers.

Nebeker:

I see.

Döring:

Further I collected publications on electron tubes, and now I found the interesting book of Van der Bijl, who was working in 1910 or 1911 on electron tubes and published the Furgotten Book in 1921.

Nebeker:

Did you ever meet Barckhauser?

Döring:

Yes. I meet him in Stuttgart after the war and I was asked whether I was interested in being his successor. I stayed in Stüttgart but did not know that I would come to Aachen at this time.

Nebeker:

Yes, I see. Are there other books that were very important to you?

Döring:

After the war a book by J.C. Slater, Microwave Electronics. Of the new books after the war — [he walked over to his bookshelf] That's a good book. These are now my bibles.

Nebeker:

I see. This is a book on gyrotron oscillators edited by C.J. Edgcombe, and one Power Microwave Sources edited by H. Granatstein and Alexeff.

Döring:

There is another book from Benford and Swegle on High-Power Microwaves. This is a German book, The Handbook of Vacuum Electronics, and for this book I have written the chapter on gyrotron together with H. Bohlen, my former pupil. He is working now at Varian in the USA.

Nebeker:

I see.

Döring:

I have written in the Lehrbuch der Hochfrequenz Technik by O. Zanke and H. Brunswig, also the chapters on electron tubes.

Influential Colleagues

Nebeker:

What people have you encountered in your career, in tubes or in other work, that really impressed you?

Döring:

In Germany I knew nearly all people working on electron tubes.

Nebeker:

Who really stand out as the great contributors to electron tubes?

Döring:

K. Steimel, W. Kleen, H. Rothe H. Rukopand, W. Schotthy. Also a very good engineer was F. Herriger.

Nebeker:

Where was he?

Döring:

He was at C. Lorenz and later at Telefunken, AEG. He is retired.

Nebeker:

You said you knew Meissner.

Döring:

Yes.

Nebeker:

Was he a very impressive person?

Döring:

For me he was not impressive, no. Brüche was a good man for publicity, but Ansauer was a scientific man. With Recknagel I had a little contact. He became a professor in Dresden. I had a good impression of Oscar Heil. He was full of ideas, but he could not bring ideas to their end. That was the trouble. During the war he was at Telefunken, AEG, Siemens, and Lorenz, all these for a short time. It was difficult to work with him when I came in 1952 to Aachen. I was a young professor, and knew nothing here. I was sitting in my room and the telephone rang: "Here Heil," who speaks? "Was ist? Wer? Wer spricht?" "Oscar, nicht Adolf, nicht Adolf!"

Nebeker:

Apart from the people you have known personally, who have been the great contributors to tube development over the years?

Döring:

I know a lot, but — you see, I have to —

Nebeker:

Name just a few.

Döring:

Professor Zenneck in Munich. Professor of practical physics. H. Busch I knew also personally. And K. Rüpfmüller in Darmstadt, Professor R. Feldtkeller in Stüttgart.

Nebeker:

One of these people you mentioned was in physics. How close was the connection between physicists and engineers.

Döring:

H. Busch was in electron optics. Zenneck was in electrical communication and radio. Feldtkeller was also in electric communication, Filter theory.

Nebeker:

Do you think in Germany there has been a good working relationship of the applied physicists and the engineers in this field?

Döring:

There is in industry good contact. Outside, not so good. The language of the physicists is different than the language of engineers. I see this in my previous institute. I am an engineer, and my successor, Professor Schmitt is a physicist. We speak sometimes two different languages.

Nebeker:

I see.

Döring:

We have good contact — we play tennis together and enjoy it.

Nebeker:

I see. There are, of course, some areas of electrical engineering that have been very much aided by work by physicists. I'm wondering about electron tube development. Once the tube was a useful device, did physicists contribute very much to improvements in tube design?

Döring:

Oh, yes. They had the ideas, but sometimes they could not —

Nebeker:

Realize them.

Döring:

Realize, yes. They cannot realize it.

Trends in Electron Tubes

Nebeker:

I know a little bit about the history of electron tubes. I know that there were some very clear trends, from the diode to the triode, to the tetrode to the pentode, and so on, putting more elements into a tube. Getting to higher power and higher frequencies.

Döring:

Yes, yes.

Nebeker:

Getting smaller sizes.

Döring:

Yes.

Nebeker:

I'm wondering if you can talk about these and other trends in the history of electron tubes. We could just get an overview of tube developments.

Döring:

Yes. The most important thing in electron tubes was in 1914 perhaps, when it was known that it was necessary to work with high vacuum. And not gas. The first tubes had gas. Lee DeForest’s had gas, but he did not understand exactly the mechanism.

Nebeker:

Right.

Döring:

And in Germany they also had gas.

Nebeker:

I'm trying to think of the famous German designer. He designed these tubes for telephone repeaters. I think it starts with an 'L'.

Döring:

Robert von Lieben, an Austrian autodidact?

Nebeker:

Lieben tubes, yes. His were also gas tubes.

Döring:

First gas tubes, and then his co-worker Strauss learned that it was necessary to build vacuum tubes. That was a very important step.

Nebeker:

Right.

Döring:

Then it went continually, one grid, two grids (1915), three (1926), and so on. Power tubes began in Germany, in 1916, by H. Rakop. There was a technological invention that made it possible to combine a glass tube with a metallic tube.

Nebeker:

I see.

Döring:

So watercooling of the ends was possible. That was in 1939.

Nebeker:

Do you know why? Was that for transmitter tubes?

Döring:

For high power transmitter tubes.

Nebeker:

Where was that work done?

Döring:

In Germany at Telefunken and at Siemens.

Nebeker:

The problem there was combining the glass and the metal? Bonding the two?

Döring:

Yes. By adjusting the expansion coefficients and by the geometry melting became possible.

Nebeker:

Yes, I see. That made it possible to go to higher power because you could water cool the tube.

Döring:

High power tubes technology is now known to all people who are working on this, but at this time it was beginning.

Nebeker:

Right.

Döring:

High power tetrodes for lower frequencies. Klystrons for higher frequencies. Magnetrons. Gyrotrons. And newer types. Perhaps the name vircator. That's a special tube, a new tube started in the USA for pulses. It is only for one shot.

Nebeker:

I see.

Döring:

SDI.

Nebeker:

It was developed for SDI?

Döring:

Yes. There was a lot of work on that.

Nebeker:

Some of these are new tube types entirely.

Döring:

Yes. But high power is the domain of electron tubes. Transistors, semiconductor devices for small powers work very well, but higher powers in principle are not possible.

Nebeker:

But if we think now back to the 1920s and 1930s, before transistors, certainly some tubes were specialized for receivers. And others as amplifiers, and so on. Can you characterize that period in tube development?

Döring:

It was a great number of different tubes for low frequencies and for low powers. In Germany, and I'm sure in the USA, it was difficult to build all these different types of tubes for military purposes. Germany developed a special universal pentode the RV 12 P2000, a so-called "Wetrimachtspose."

Nebeker:

When was that developed?

Döring:

Oh, during the war. 1940 perhaps. This tube was possible for use in repeaters, in amplifiers, oscillators.

Nebeker:

It was designed to be universal?

Döring:

Yes, yes. But it was the same in the USA, and the same in England.

Nebeker:

There was also, of course, the development of smaller and smaller tubes.

Döring:

Yes.

Nebeker:

Especially for military use.

Döring:

At the end of the tube time, before the transistor came, some places developed the so-called nubistor. [sp?] That's a very small electron tube. Perhaps these dimensions [indicates with his fingers]. But there was no interest in this small tube.

Nebeker:

I see. I'm asking these question because when I try to look at the history of the electron tube, it seems very complicated. You know, there were all these hundreds of types of tubes developed.

Döring:

There was a picture published in the paper Electronics in 1939.

Nebeker:

A big tree —

Döring:

A big tree of electron tubes.

Nebeker:

I've seen that picture, and I'm just hoping to get from you simpler ways of thinking of this development of tubes. You have made some things clear, where there were certain trends. I suppose it also was important to make the manufacturing easier.

Döring:

Yes.

Nebeker:

To see if you could achieve the same effect with a tube that was less expensive to manufacture. You mentioned this one technique of bonding metal and glass. Of course earlier there was recognition that high vacuum was important. What were other technical things? Maybe the bakelite base, or what were some other important manufacturing techniques?

Döring:

An important technique was the peste [?] development. That's a chemical work.

Nebeker:

Oh, the right kind of metal for the cathode?

Döring:

Yes, the metal. It is a mixture of barium and strontium, and so on. At first it was tungsten wire. After the tungsten wire came a tungsten wire combined with thorium.

Nebeker:

Thorium, yes.

Döring:

Its work function was lowered with thorium.

Nebeker:

I see.

Döring:

Then came the indirectly heated cathode.

Nebeker:

That was an important development.

Döring:

Yes. Thereby ac-heating of the cathode became possible.

Nebeker:

Both of those things you mentioned, the moving to thorium and the indirect heating were to get a better emitter in the tube.

Döring:

Smaller heating power and higher electron emission, yes.

Nebeker:

Yes.

Döring:

And smaller dimensions.

Nebeker:

I see. Were there new materials continually being used for the cathodes?

Döring:

Yes. For example, osmium and scantium. Most people have never heard the name, "scandate."

Nebeker:

Scandium is an element.

Döring:

Yes, yes.

Nebeker:

So scandate is —

Döring:

Perhaps it is a mixture.

Standardization of Electron Tubes

Nebeker:

I see. So one could say that there was a continuing development with the metal used for the cathode. What about the base of tubes? What standardization was there in the pins, the connectors of tubes? Was there agreement that they would be certain sizes?

Döring:

There were in the different countries standardizations, but they were different in different countries.

Nebeker:

Right.

Döring:

From one to the other.

Nebeker:

In Germany what important agreements were reached?

Döring:

Agreements between Telefunken and Philips, together with the Netherlands. Also to some extent with France. But in England it was another.

Nebeker:

Another system. When did those companies make agreements about the tube types?

Döring:

Oh, in the 1930s.

Nebeker:

In the 1930s.

Döring:

Yes.

Nebeker:

That meant that there would be certain patterns of connections.

Döring:

Yes.

Nebeker:

And that the tube must —

Döring:

That they could be changed, yes.

Manufacturing Techniques

Nebeker:

I see. Were there important new manufacturing techniques that came along, making it less expensive to manufacture tubes?

Döring:

This I learnt at Lorenz. They were good in developing, pumping and melting for more protection.

Nebeker:

High vacuum.

Döring:

Yes, but better perhaps was Telefunken’s work. They had more experience. Telefunken made in the 1914. But I will give you some of my later publications.

Nebeker:

Are these copies for me?

Döring:

Yes.

Nebeker:

Thank you.

Döring:

That's in English. Last year I gave a lecture at Sao Paulo on high power electron tubes. There are some pictures. One Siemens tetrode, gyrotron and klystron. Philips klystron.

Nebeker:

Thank you.

Döring:

And The Development of Microwave Tubes in Germany, Part I and Part II, from 1920 to 1945. Since the end of the war microwave tube development was forbidden for twenty-five years.

Nebeker:

Do you think German engineering was much hurt by that? Was it much damaged by that prohibition on developing these high frequency tubes.

Döring:

Not too much.

Nebeker:

When was it permitted again to develop microwave tubes in Germany?

Döring:

It was forbidden from 1945 until 1950. Five years.

Nebeker:

I see.

Döring:

This was a special cavity, working at 30cm on the pump and giving 100W, magnetron development in 1938 by F. Herriger. This was my old klystron, the AEG 1940.

Nebeker:

Thank you.

Döring:

I gave a lecture in 1988 at Karlsruhe, on fifty years klystron development.

Post-Transistor Trends

Nebeker:

I wonder if you could summarize developments after the transistor developed and became available. Of course, the electron tube survived in high power areas.

Döring:

Yes.

Nebeker:

For all applications? All high power?

Döring:

Yes, they made transmitters for 1kW with semiconductors, but it is a difficult construction.

Nebeker:

These are the two main developments. Are there any other smaller areas in which electron tubes have survived?

Döring:

Electron tubes for the highest frequencies. The highest frequencies were one terahertz [1Thz?] according to 0.3 millimeters. One terahertz cannot now be made by semiconductors, but with tubes it is possible.

Nebeker:

I see. So, for the very highest frequencies, and for high power and for picture tubes.

Döring:

Yes.

Nebeker:

I see.

Döring:

But perhaps it will be possible in time to use semiconductors to make these except for high power.

International Connections During War

Nebeker:

In Germany, in the period you worked on electron tubes, in the 1930s and 1940s and so on, were you reading the literature from England and the United States regularly?

Döring:

When I was working on tubes, partly. In France I saw a little during the war, since formerly Thompson was also a good contact with General Electric, like Lorenz.

Nebeker:

I see.

Döring:

Then I had the chance to go to Paris.

Nebeker:

During the war?

Döring:

To see some klystron oscillators and young engineers who were working in France, at Thompson. They then came to Germany and learned with Lorenz in my laboratory.

Nebeker:

I see. This is during the war?

Döring:

During the war, yes. They made efficiency calculations for the Klystron.

Nebeker:

Did that mean that you could see some of the American and English literature? The journals?

Döring:

A little.

Nebeker:

But mainly in the 1930s and 1940s it was a national internal development of tubes? There wasn't a lot of —

Döring:

Not official, no.

Nebeker:

What were the main journals in Germany for publishing results about tube development in the 1930s?

Döring:

High Frequency Technique au Elktroakastik. Published by Zenneck and Die Telefunken Rühr, a non-periodical Telefunken journal.

Nebeker:

That was the main journal.

Döring:

I had the possibility to write for Zenneck during 1936 until the end of the war, short reports on different publications. I learned much from writing these.

Nebeker:

This is like referees’ reports of articles submitted to Zenneck?

Döring:

Yes, I did these.

Nebeker:

Oh, I see, you were writing abstracts of articles.

Döring:

Shorter ones, yes. It depended on my time. It was good work, and I learned a lot. My firm paid money for me, for my name was known as a member of AEG, or Lorenz. The paper paid also. I received money twice.

Nebeker:

I see. Did that allow you to go to conferences?

Döring:

I went to conferences also, yes.

Nebeker:

Basically you were given an American, French or British article, and you prepared an abstract for it.

Döring:

Yes. Zenneck sometimes told me, "Please write a paper on this paper." But he told me also, "If you find a paper that I did not find, write." Which was very good.

Nebeker:

Is it possible to summarize what areas Germany was leading in tube development, and in what areas the US, or Britain were leading?

Döring:

It was —

Nebeker:

It was always changing?

Döring:

Yes. Sometimes one, and then another, for example in USA most microwave triodes were designed in metal-glass technology and in Germany, metal-ceramic technology was very successful.

Nebeker:

Yes. So there was a lot of sharing and common development.

Döring:

If you are interested in literature on tube development in Germany, there is a special work from H. Gundlach, the Lauftzeitrohren Deutsche Fiat Review [volume 15, pgs. 114-146, 151-217].

Nebeker:

Oh, yes, I know of those Fiat Reviews.

Döring:

Yes.

Nebeker:

I see, so he did a Fiat Review on electron tubes?

Döring:

Yes. A chapter in Volume 15, written by Gundlach. Very early, 1947.

Nebeker:

And published in 1948, I see.

Döring:

That is a good paper.

Nebeker:

Those are a good source of information, those Fiat Reviews.

Invention of Reflex Klystron

Nebeker:

Those are the questions I had for you. Are there any comments you would like to make about your career, or the history of tubes? I would be happy to have them on tape.

Döring:

I wanted to know who invented the reflex klystron —

Nebeker:

So you tried to determine who invented it.

Döring:

I do seek to find this. I know that the Varian brothers had from 1937 to 1938 a patent on it. But who it for the first realized time? I know that in 1945 John Pierce was the first who published specially on the reflex klystron. Very good theoretical work, but in the practical work I could not read something. I spoke with an English colleague, and he told me the English were the first to build a reflex klystron. Before the beginning of the war they knew that it was necessary to work with radar not at fifty centimeters, or one meter, but at ten centimeters. But they had for the receiver no oscillator. Therefore they were forced to develop some quickly, and they found two ways. One way was the Heil generator, and the other was the reflex klystron from the American Varians.

Nebeker:

They learned about it from the patent application?

Döring:

Yes. I will try to find it. And that was the reflex klystron. They built both tubes and found that the reflex klystron is cheaper and not as complicated as the special magnetic field, so they built the reflex klystron.

Nebeker:

I see. For ten centimeter waves and then for 3cm.

Döring:

Herr Spinner. He is an older man. A pupil of Professor Meinke in Munich. He has written a paper on the electron tube. But it is not finished. He lives in Munich, but he is ill. He is very ill and I fear he will not continue.

Nebeker:

So this is a very recent, a 1993, publication on the history of electron tubes.

Döring:

Yes, but it is not finished. It is not published. This is a working paper.

Nebeker:

I see. It is a draft of it.

Döring:

These are highlights of the whole section.

Nebeker:

I imagine you know the book by Gerald Tine, The Saga of the Vacuum Tube.

Döring:

Yes.

Nebeker:

I just wanted to ask your impressions of that book. Is it reliable?

Döring:

It is good, but not always correct.

Nebeker:

The Callock, you're talking about here? Meters to Microwaves. Yes, I know the book.

Döring:

Yes, yes. I also recently found the tube which was the first tube I bought as a young pupil in 1926. It was a Philips tube. A B-6 tetrode.