(005W)
Excerpt from “NEC Total Engineering of Electrical Communication”
No.22, Feb. 1954

IIII: Vacuum Tube (p.p.: 66-80)- 11 Pages
4.1. Summary
It is our pleasure to see that many of NEC branches have grown with flower, and broughtpresent success in our vacuum tube business after 20 years from its birth. In the following
sections, we intend to explain process of growth and present situation in each area, but first,
wish to describe our general philosophy here as: quality mind, new technology, process ofprogress changed by world situation, mind for future growth, etc.
We have started our challenge for vacuum tube production in 1931, and was solely forvoltage amplifier tubes and power amplifier tubes for repeater in wired communication
system. And then started trial production of transmitting tubes from 1933. It included
water-cooled type, air-cooled type and mercury-vapor rectifiers for wireless equipment in
HF broadcast transmitters and VHF transmitters. Thus all of such equipment demanded
extremely high quality. The foreign partners we worked together at that time wereWestern Electric Co., STC Co., etc. which were top rated companies in the world, and thevacuum tubes we have challenged were based on their products. Therefore our mind against
quality was:a. High reliability
b. Uniform performancec. Long life
This policy has never been changed more than past 20 years, and will never be changedin the future either. As the result, price of our products were quite high in the past, andmaybe similar trend be seen at the present, too. A long time ago, when cost of a radio tube
was approx. 1 yen, a repeater tube was 25 yen. But the fact told us that it should be paid
off for such application i.e. high quality and long life tubes. Unfortunately, quality of our
products have dropped considerably during the war particularly at the end, but this was
because all materials were in short supply, and therefore could not keep our quality
standard. We spent every effort to maintain our reputation.
1

By talking this way, people may think that we are too conservative and only try surething. But fact is totally reversed, and we have been very aggressive against new technology,
and in introducing new technique, researching new theory and apply the result for new
products, etc. were always running about top among the industry. In early days, we haveadopted oil diffusion pump as the forerunner, and more recently, completed kovar sealing,
succeeded sealing with arc welding for large transmitting tube, introducing powdered glass
stem, etc. were few examples. A 50kW transmitting tube for short wave was the first one in
the world. After the war, we have started study in micro wave tube, metallic reflex klystron,
planar tube, etc., and built our own footsteps. We succeeded production of MT tubes in theearliest among Japanese companies as well known fact. Recently, we have completed
preparation for sub-MT tube production, and again surpassed others. As to applying quality
control, we were again fastest, and it has assisted birth of new products quickly as describedearlier.
Our 20 years has passed, but during this period, world had greatly changed as
Manchurian incidence to WWII, and finally reached recovering stage of present. Our
situation in tube production has passed various epoch. We will list several of them looking
back our trail:First, when we started up this business, our work space was only one corner of anexperimental room in the engineering department. Little later, it was assigned as inresearch section, but still no individual organization existed, and some engineers assigned
for vacuum tube research were in research group, and others were in trial section, etc.
Under those conditions, however, TW-504-A tube for 10kW short wave transmitter has
completed.
In 1934 vacuum tube group has born in research section, staff associated with tubes
were all together, but still only less than 50 staff. In this condition, TW-502-A tube installedin 100kW transmitter was born. In 1936 we finally upgraded to individual vacuum tube
section, and at the same time, moved into new Tamagawa factory. It was still a small section
at first, but gradually expanded, and research, design, production, etc. were organized as
separate groups. At the end of 1940, research department has born, research work hasconcentrated into the department, and design and production work were reorganized in thefactory. In 1942, matching the war time demand, a large organization, vacuum tube factory
was organized, and inflated to 3,000 people including student assistants. In April 1943, welost half of activity in the factory because of fire. But fortunately, it was recovered in 2
months with assistance of army and other factories. From early 1945 bombing by U.S.
aircraft has getting severe, and moving to Ohtsu branch factory, and shift part of activity
to Niigata has started, and when Tamagawa factory has become almost empty, the war has
ended. After the war, facilities have gradually returned, and started as the first production
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division. At that time, first order to reopened factory was from U.S. occupation forces, andwas large transmitting tubes for high powered broadcast transmitters. And next,
communication tubes to reactivate damaged wired communication system were required,and at the same time, quality improvement of the products were highly demanded. For thereason, U.S. military headquarter has dispatched QC staff and educated us. And we haveaccelerated improvement of quality of our products. We presume that it was the first caseof establishing quality control organization in Japan. In February 1947 inspection division
has born to organize QC activity, performed product inspection by the independent
organization. After this, research and design staff have separated from the factory andformed vacuum tube engineering section, merged into engineering division and today’sorganization has materialized.
By looking at actual products, we can find various processes. In the beginning, it was
mostly triode tubes for wired communication, and then water-cooled tubes, air-cooled tubes
and mercury vapor rectifiers. X-Ray tubes were one of others born around that time. And
then short wave/ in high power age has followed, and in the other hand, pentode
communication tube development associated with unloaded cable took place. As pressure
by war comes, high powered pentode series in transmitting tubes was demanded, and mass
production of pulse transmitting tubes and CRT were ordered by invention of wirelesslocator. At that time, our factory has continued expansion to answer the military demand.
After the war, as vacuum tubes were one of the most needed items in recovery process, muchfund has spent for it, and production of large transmitting tubes and communication tubes
have recovered quickly. Next, one of the industrial application, high frequency heating, hasrealized, and shown active situation. And to fulfill market demand, active movement was
required as; development of MT and sub-MT tubes, mass production of CRT to accommodate
TV broadcasting, etc. In the other hand, development of micro wave tubes were accelerated.
The application of vacuum tubes to industrial field has further increased, and expected to
be a big market in the future. Therefore preparation for such movement has also carried on.
The details of these products should be covered in the following articles, but the writer
wishes to add one thing here: The vacuum tubes should have a great future as its
application increased, and for such usage, our motto as “high reliability”, ”uniform
performance” and “long life” are strongly demanded, and therefore intend to pay continued
effort in keeping quality and developing new products.
By Hidehiko Nishio34.2. Transmitting Tubes and Thyratrons
In 1932 our chief engineer Dr. Shoji Kobayashi visited Europe for technical investigation,and especially spent one year at French laboratory L.C.T. under I.S.E. for studying
production technique of vacuum tubes, and returned to Japan in 1933. We started producing
transmitting tubes since 1933 utilizing the result.
4.2.1. Products before the war(i)TW-502-A
The representative product during the cradle age must be a water-cooled triode having

120kW of output, TW-502-A. Therefore we can say that our transmitting tube production
has started with high powered tube. This was a double-end type, filament was of puretungsten, single phase with coaxial-shaped terminal. On the grid and filament terminals,
radiator made by silmin are installed which was very modern design for that time. The
anode voltage of 20,000V was a record breaking value, and we are still holding hightechnology since then. This tube was used in final stage amplifier and modulator of 100kW
broadcast transmitter, but its production has discontinued at the present.

(ii)

QC-715-C
This tube was made for rectified power supply of the above mentioned transmitter.

The average anode current: 15A, maximum PIV: 20kV, with large indirect heated oxidecoated cathode, and was a record making product completed after great effort of ourengineering staff. This tube has still been used as power supply of 50kW short wave
transmitter for overseas as described later.
4

(iii)

TW-504-D

This was a water-cooled transmitting tube of 15kW output which was popular to earlyexperts in wireless field. As letter D shows, it was fourth modified model since its first
design. It had good reputation for high stability and long life.
(iv)

TC-517-A and TC-522-A

These were also popular air-cooled transmitting tubes. The former was 750W output,
and the latter was 1.5kW, and both of them had thoriated tungsten filament. These uniqueconstruction were by special design of Western Electric Co., having excellent frequency
characteristics and usable up to 22Mc. These tubes had high reputation as long lived aircooled tubes, and are still used in our transmitters today.
(v)

TW-530-B
In 1937 a 50kW short wave transmitter for overseas broadcast was installed in Nazaki,

Saitama by International Wireless Co. This was the world highest powered short wave
transmitter made by us, and this TW-530-B used as last stage amplifier was of course theworld largest short wave power tube at that time.
For stable amplification up to 22MC, reducing inductance at grid input portion, making
dimension of its operating area smaller for reducing grid temperature in order to minimize
grid emission, etc. were applied. As the result, anode dissipation per unit surface area has
increased, and difficult problems i.e. cooling of glass part of grid/anode and filament/anode,etc. have finally resolved. This type was both-ended water-cooled type, and glass portion
was forced air-cooled. This tube is still used actively for overseas broadcasting.
(vi)

MD-546-C

In 1938 an air-cooled pentode with 250W output has completed. This tube was used in
final stage tube with first suppressor grid modulation. This was for our shipboard wireless5

transmitter. This tube was not only for the first suppressor grid modulation, but also record
making as 250W crystal oscillator. As its driving power was extremely small, large
oscillation output could be obtained without damaging crystal vibration element in the grid
circuit. One item noteworthy in the history of pentode transmitting tube development.
(vii)

MC-580-A

Following completion of MD-546-C, we marketed MC-582-A (500W output), and in 1940
introduced MC-580-A with 1.5kW output. By those pentodes, wireless equipment having
2kW output was realized in much smaller size. The former was being used in Nakano
station of national police station and Kemigawa station of national communication station
for some time, but after introduction of movement for unifying tube type numbers, this tube
was replaced with 6P70 which was an improved model.
(viii)

TW-558-A

In 1940 TW-558A which was our second 120kW output class tube has completed. This
was the newest designed tube at that time, filament was 3-phase heating to reduce A.C.
hum with tri-axial terminal, smooth shaped both-end type. The best layout was adopted toreduce A.C. hum after ample research. And our first 100kW broadcast station in Taiwan
using this tube has installed with Doherty modulation system as the forerunner. Thistransmitter has still been working today. But new production of this tube has terminated,and 8T21 tube as the successor is under production now.
(ix)

TC-1507

In 1944 Japan’s first UHF multi-channel telephone system with 670MHz has installedin Japan National Railway’s Aomori-Hakodate line by us. For the final stage of this system,
our TC-1507 tube was used, and no competitive product existed which can produce 5W of
output at this frequency. This tube was with thoriated tungsten filament, and anode andgrid leads were at both ends and designed as operated at the center position of lecher tuning
circuit. This tube has still been in use today, and marked the first in UHF transmitting tube.
(x)TR-593-A, TR-594-A, TR-1501
During the war, we developed high peak powered forced air-cooled tubes for wave finder

or wave locator. TR-593-A had peak output of 10kW, TR-594-A was 50kW, TR-1501 was
30kW. Those were first examples using copper anode and thoriated tungsten filament, andanode voltage was high 10,000V. After paying great effort for obtaining high vacuum,
considerably long life was obtained which was unusual for pulse use. This result made basis
for use of thoriated tungsten filament to large powered transmitting tubes today.
64.2.2.

Products after the war

4.2.3.

Thyratron(i)

Products before the war

Excluded---Ed.

Our first thyratron was XB-712-C, argon gas filled type produced in 1935. This tube wasused for relay, voltage control, saw-tooth wave generator, etc. After this, several mercuryvapor type thyratrons were made. Among those, record making model was XC-732-A. This
tube was used in 100kW transmitter installed in Taiwan in 1940 as described in transmittertube section. It was used for shutting down the power source within several cycles if thelast stage tube had internal flash. The surge current in this case should reach 100A, andtherefore thyratron action must withstand against it, thus record making item at that time.
The representative products from 1933 through 1945 are shown in table 4.2.6.
XB-767-A was argon filled type made in 1944. It was tetrode construction differed fromolder type, and anode, grid and cathode were all in rectangular frame, and the frame wasdivided into 2 sections shielding anode and control grid by screen grid. Feature of tetrodetype is low control grid current, and therefore can be used in high impedance grid circuit,and also have steep starting characteristics. Also starting characteristics can be changed
by varying screen grid potential. At the present, an improved type XB-785-A is in production.
(ii)

Products after the war

Excluded---Ed.

4.3. Small Tubes for Communication
Small tubes are general definition of tubes covering detect, rectify, voltage and power
amplify, frequency conversion, etc. having less than 20W of anode dissipation. Within the7category, we have separated production of major part to newly established New NEC, andour company is concentrated in tubes for communication purpose. The communication tubes
include tubes for measuring instrument, part of sound system and industrial use, etc.
4.3.1.

Wired Communication Tubes

This category has the longest history and tradition, and hold the main stream of NEC’s
small communication tubes. Its history, products and their performance and process ofimprovement have described in NEC Nos.10-12, and 16, but the summary is shown here forconvenience:

Table 4.3.1(i)Variation and Improvement of Wired Communication Tubes
Please see Table 4.3.1. ---- Ed.
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(ii)

Process of improvement
The improvement process has planned since early 1946, and especially on CZ-501-D and

CZ-504D which are lifeline of main communication system. The major items of process are:Shown in Table 4.3.2. ---- Ed.

Process of improving Type CZ wired communication tubes
Item
Anode and other metal parts: Fe→Ni (N-tube)

CZ-501-D

After Sept.'46 partially, after Oct.'46 totally

Stem : Pb glass→Ka glass (NK-tube)
Getter: Mg→Ba→Ba

CZ-504-D

Totally after Nov.'46
After Sept.'46 partially, after Oct.'46 totally

Mount system applied to assembly

Dec.'48

G1 support bar: 0.6→0.8mm dia.

Feb.'49

G2 support bar: 0.6→0.8mm dia.

Feb.'49

G1 support bar: Ni→Steel alloy

Nov.'50

Feb.'49

G1 wire: →adopt Gold plate

Mar.'53

Apr.'49

Cathode→adopt emboss system

Oct.'51

Cathode→adopt special Ni material

June'51

Sept.'51

Grid support bar→adopt stopper system

June'51

Sept.'51

Adopt double mica for improving insulation

Feb.'53

Adopt phenol resin for base cement

Oct.'49

Adopt glue for undercoat of base & cap

Oct.'49

Adopt anti-humidity paint on base top

Sept.'49

Base cement→Silicon Resin

July,'52

Table 4.3.2. Process of Improving Type CZ Wired Communication Tubes(iii)

Results after improvement

As result of above mentioned improvement, average life of the present products exceeded
100,000 hours compared with several thousand hours when the war has ended which is adramatic improvements. See Table 4.3.3.
9

SampleN.G.

Type No.
StationEst. Avg.
Date Inspected

No.

No.

Life

Kounosu

CZ-501-D

30

8

Aug.10,'51-July 31,'53

130,000

Takahagi

CZ-501-D

154

16

June 20,'52-Apr.22,'53

122,500

Mito

CZ-501-D

42

4

May 15,'52-Apr.22,'53

ー

Mito

CZ-504D

3

0

Sept.15,'52-Apr.22,'28

ーTable 4.3.3.
(iv)

Improvement plan on CZ tubes with reduced cathode temperature

When tubes are operated for a long time, Barium scattered from cathode tend to result
in reduction of insulation and create grid emission, and therefore current CZ tubes areoperated with If of 0.95A instead of designed 1.0A intentionally. Also as relation between
lifetime L and cathode temperature Tk against emission is: log L ∽ 1 / Tk, and therefore
reduction of Tk at the rated condition makes lifetime longer. Therefore improvement planof CZ tubes with reduced cathode temperature are carried on since early 1952. Reduce Ef to
3.0V for CZ-501-D and 5.0V for CZ-504D.

By this change, Tk should be reduced by

30oC on the former, and 25oC on the latter. The estimated lifetime of NEC’s CZ-501D usedcurrently is 130,000 hours by the accelerated life test conducted at NTT’s Communication
Research Lab., and 120,000 hours by our test, and these figures approximately matches theabove mentioned actual operation results. In the other hand, if cathode temperature has
reduced by 30oC, estimated lifetime should be approx. 400,000 hours i.e. amazing value
equals about 45 years.
In the same way, present CZ-504D has lifetime of approx. 100,000 hours, and if cathodetemperature has dropped by 25oC, then estimated lifetime will be approx. 220,000 hours.
This estimate, of course, excludes all possibility of failure other than emission. We sincerely
hope that current problem on power supply and maintenance at relay stations and improved
communication tubes be in actual use soon.
(v)

Miniature Communication Tubes

Excluded---- Ed.

4.3.2. GT type Communication Tubes and Metal Tubes
4.3.3. Miniature type Communication Tubes
4.3.4. Sub-MT Tubes

Excluded------ Ed.
10

Excluded----- Ed.

Excluded----- Ed.

TW-502-A

TW-530-B

TW-558-A

120kW Output

60kW Output

120kW Output

1937

1940

1934

For Short Wave

Note: Photos from “History of Vacuum Tubes” (Japanese Version) ------ Ed.

11