(004W)

Excerpt from “55 Year Step of Japan Radio Company”(1971) in Japanese
Chapter 16: History of Vacuum Tube (I)- Before the war(p.p.:280-285)- 7 Pages

1) The Beginning
When our company has established, the wireless equipment in use was sparktransmitter and crystal receiver. As to the vacuum tubes, post office and navy/army
have just started investigation, research and trial production.
But in our company, we forecasted that the age of wireless equipment using vacuum
tubes will come in the near future, and decided to proceed full scaled R & D project ofvacuum tubes and wireless machinery using them. In March, 1917, this plan has
materialized, a vacuum tube factory has built and R & D work has accelerated aiming
completion of tube receiver for ships. This was one year behind TEC’s start of R & Dproject.
In the next spring, the first vacuum tube for detector, C1 has born, and named asLumion. And in September of the same year, completed a receiver for ship using thetube, and received good reputation. This was a low vacuum triode, so-called soft valve,and its anode was made of aluminum sheet, and grid was spirally wound nickel wire.
As exhaust process was only with a rotary pump, and therefore vacuum level was low.
Next, in September 1920, we developed a receiving tube C3 by navy’s order. Thiswas our first triode for amplifier, and hard valve using a diffusion pump. At this time,army called it as vacuum bulb, and navy called it light bulb.
As our high vacuum process has advanced, development of transmitting tube wasaccelerated from about 1921, and in June of the year, first transmitting tube TR 1 with
input of 10W was completed. At the same time, our factory has modernized, andpreparation has completed for development and production.
As the result, TR V with 100W, TR VI with 250W, TR VII with 500W input tubes
were completed in 1922, and in the next year, transmitter for ship using these tubes
1were designed, and in March 1924, 500W input transmitter has first installed in Meiji
Maru, a training ship of Tokyo Marine High School. And also, supplied the similartransmitters to post office and army, and made record as their forerunners as domesticvacuum tube transmitter.
The development of transmitting tubes has further advanced. In 1923 TR IX having
1.5kW input was completed, and in next year, a vacuum tube wireless communication
system with 3kW input (using two TR IXs) has supplied to central weather station, andstarted weather forecast broadcast from February, 1925. This transmitter made arecord of highest power for domestic production at that time.
In the other hand, as to radio receivers, each company in Japan started active
advertising preparing for start of radio broadcast, and therefore demand of receiving
tubes have inflated. We have marketed C7 for detector, C4C for audio amplifier andC4D for H.F. amplifier in October 1924. Our catalog at that time said “C7 has a great
sensitivity, and usable for long time. Not many of such product exist even in the westerncountries’ ”.
Tough problems in receiving tube production about that time were burning offilament wire, reduction in emission, and difficulty in development of good cathodematerial with low heating power and high efficiency.
We started research in this area, and in the spring of 1925, produced a receiving
tube C12 having dull emitter i.e. thoriated tungsten filament with low temperature
cathode. After this, serious research has continued in this area.
As to the oxide coated cathode, application in receiving tubes by Western Electric
Co. in U.S. has introduced in 1926, and started development here first time, and convert
to eliminator radio in Japan has accelerated. In 1929 this effort was fulfilled and usedin many radio receivers.
Also at this time, research on the iron resistor tube for power supply voltage
stabilizer started by request of navy. This was to be used in 60-80V of working voltage
at 135mA of current, and big volume of this have produced up to approx. 1935.
2) Transmitting Tubes
In mid. 1920s, vacuum tube transmitters were getting popular in Japan, and at thesame time, short wave age was about to begin. At that time, our company was alreadycooperated with Telefunken Company in Germany, and was planning a big progress in
R & D of vacuum tubes and wireless equipment.
Under this policy, continued improvement in transmitter, tried to unifying toS-series of transmitting tubes, and spent effort in development of short wave
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transmitting tubes.
First, in 1928, completed S300 (with 6kV of anode voltage and 1kW of input), animproved version of TR VIII (10kV of anode voltage and 1kW of input), and it has
greatly contributed to transmitter for ships, and also completed various newspecifications. And in 1929, moved the factory to Osaki, expanded the facility,
accelerated development activity, and organized production activity of S-seriestransmitting tubes. For those transmitting tubes, pure Tungsten wire was used forfilament.
Also, for application of thoriated tungsten filament to transmitting tubes, needed tosolve problems on increasing emission capability and stability. In 1932, after solving
those problems, RCA type transmitting tubes; UV-203A, UX-860, UV-812, UV-861 etc.
were produced. In those days, U.S. styled tetrodes were used much, but after developing
transmitting pentodes by technical assistance from Telefunken Company, completed
the series by the end of next year, and saw pentode age in transmitting tube.
3) Patent Right of General Electric Company
The vacuum tube production by our company was expanded smooth up to late 1920s,
but in February 28, 1930, a patent which 3/2 power law on the high vacuum tube heldby G.E. has extended, and as TEC who held this patent insisted charging toughconditions. As the result, all of other Japanese tube makers faced a confusion, and somecompanies had to terminate tube production.
After tough negotiation, we were allowed a small part of high vacuum tube
production. It was a big problem in our tube development history, not only for ourcompany. We, therefore needed establishing a new policy as shown in the following
sections. By the way, this patent has extended up to February, 1935.
4) Expanding Plan of Tube Facility and building Senzoku Factory
In 1932 we made an expanding plan of tube facility during waiting resolution of thepatent. This policy aimed tube development without infringing G.E. patent.
For this policy, we picked up two major plans i.e. R & D of microwave tube and its
associated equipment, and same of discharge tube, and immediately started proceeding
it. This was based on our engineers’ strong will for making bright future of vacuum tube.
First, hiring research engineers (electric, physical and chemical experts) andtraining them in Telefunken Company are planned, and gradually executed.
Also continue expanding research activity and factory, and in 1934 moved to3

Senzoku in Tokyo. The space was 660m2. By this expansion, we occupied 20% of whole
Japanese transmitting tube production, and reaching one million yen’s sale in the year.
5) Research on Micro Wave Tubes
We started R & D project on micro wave tubes since 1932 by expecting future success,and first of all, opened a research room. At this time, it was far from realization of microwave technology.
This research activity led to cooperation between Japanese navy’s researchlaboratory next year, and then same thing has realized between army’s laboratory.
By around 1941, our microwave laboratory member reached 300.
6) Research on UHF Tubes
As to UHF tubes, we started from early days, but in 1934, obtained data on RS329g
tube (wavelength: 5m, output: 500W) from Telefunken, and the activity has rapidlyadvanced. By next year, U242Tg (wavelength: 3.5m, output: ar. 500W) has developed.
This tube has used in UHF medical treatment machine named Aloka, and mass
produced ‘till even after WWII.
In 1936, U330T was used in Japan’s first TV broadcast experiment. This tube wasan UHF tube having 2.5kW of output.
In 1941 a tube with wavelength of 9m and output of 250W has developed and usedin blind landing system of aircraft adopted by army.
7) Moved to Mitaka Factory
In 1938 we have moved into newly built Mitaka factory expecting a bold leap ofresearch and production. This factory had 1,320m2 of tube research division area and1980m2 of transmitting tube factory area. After moving, we put a great effort in top
secret research in micro- wave tubes, and transmitting pentodes developed with
Telefunken’s technical assistance, and various discharge tubes headed by Sendaitronlead by Prof. Watanabe of Tohoku University, and also proceeded research on getter
materials.
8) Development of Discharge Tubes
Production of hot cathode mercury vapor rectifier was started from 1929, and4

marketed in 1932. But in shipboard wireless equipment, frequency of power source was400Hz, and had poor voltage stability. Therefore a problem arose for short life ofrectifier tubes. As a remedial work, utilization of getter, use of special material forcathode (mixing activated impurities) etc., were applied, and adopting a speciallydesigned model against 400Hz of power line, and finally succeeded completion of
products suited for shipboard application.
Also completed Type A Sendaitron by leadership of Dr. Y. Watanabe of Tohoku
university, and widely marketed as discharge tube for magnetic fault detector, metalwelder, magnetizer, etc. We added types B, C & D later for similar application.
9) Receiving Tubes
Entered new emperor’ age as Showa, copy of U.S. type tubes were getting popular,and in 1927, NM201A with thoriated tungsten filament, and in 1929 NM226R, NM227R,NM112A, NM80K, etc. were completed, and mass produced.
But we have decided terminating production of radio products in view of war time,and concentrated production of military products. In 1939, manufactured Telefunken
NF2 used for landing position locator for aircraft, and in 1941, completed Telefunken
type receiving tubes RE3 and FM2A05A, and supplied them to military offices.
FM2A05A was an all- purpose tube with an excellent characteristics used in aircraftreceiver. But it required high production technique, and many engineers and workers
were concentrated, but its required volume was too much for our capability. Therefore
asked Matsushita Electric Company for help by giving our know-how, but still could not
fulfill military demand, and also asked manufacturing in TEC and Kawanishi MachineCompany as well.
We have acquired Hamamatsu factory of Toyo Spinning Company in 1944 by
military direction for additional production, and started producing receiving tubes andgetter. But within a year from its start, faced repeated bumming from U.S. aircraft andships, and was totally destroyed with many loss of life. This was only casualty by thewar in our company.

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Earliest production of Receiving Tubes by JRC

Lumion C1 by JRC (1918)
Photo from OTB Vol.37-3, Aug.,1996
By John W. Stokes

C4B

6C4C (1924)

NM90

NM180

(First Dull-Emitter by JRC)

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