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Excerpt from “50 Year History of Tokyo Electric Company”(1940) in JapaneseRadio Equipment (p.p.:424-454 )Part I: Receiving Tubes (p.p.:424-437)- 17 pages

Foreword
In recent scientific field in Japan, nothing should surpass radio technology in viewof its surprising development and most effective application. Looking at the radio
broadcast having nearly 5 million listeners at the present, or wireless communication
between land and ocean, it is really amazing situation.
However, if we search source of such development, they are solely as a result oftechnology of vacuum tubes, and therefore, more than 20 years of our vacuum tube
production history must be long remembered as a glorious memorial tower.

1) Dawn of vacuum tube industry

In 1904 Diode vacuum tube has found by Fleming, and Triode has invented by
deForest in 1907. And then hard valve concept has followed by Langmuir in 1913 which
contributed much to the development of vacuum tube industry. But major advancement
came after WWI, and research of vacuum tube occupied a major field of national
military interest. In view of this, our company started research project of vacuum tube
in 1916 based on our experience of vacuum technology gained by light bulb production.
And in 1917 succeeded manufacturing nation’s first vacuum tube named Audion.
In 1919 we produced so-called French type tube with a cylindrical anode for army
as his standard product, and about the same time, produced a transmitting tube with１

Tungsten spiral anode to post office. In 1920 we manufactured navy type tube by his
request, and also supplied type D Pliotron in 1921. The name Pliotron stood for ourtransmitting tubes.
After 1920 demand of vacuum tubes increased, and the production technology finally
got out of prototype stage, but the catastrophic earthquake occurred in 1922 which has
destroyed our research and production facility completely, and many of our experienced
research staff and documents have lost by the accident. But our effort afterward as achallenge given by heaven finally surpassed the difficulty.
The first Japanese radio broadcast started in 1925, and production of vacuum tubes
has become real stage of advancement.

2) Progress of Receiving Tubes

a. Radio Broadcast and Receiving Tubes

The word Radio sounded as a big charm among general public when the radio
broadcast has started in U.S. in 1920. Many R & D projects were held in various fields
of Japan as well. In our company, UV-200 (soft valve) and UV-201(hard valve) were
manufactured for radio amateur, and marketed under the trade name “Cymotron”.
Cymo stood for wave in Greek, and therefore meant as “component for wave”. This
name Cymotron was used only for transmitting tubes after March, 1932, and all ofreceiving tubes were called “Mazda Tube” thereafter.
UV-200 and UV-201 tubes described above were using pure Tungsten filament, but
in 1924 we have succeeded production of Thoriated Tungsten filament, and marketed
UV-199 and UV-201A with it. This has received enthusiastic welcome of the radio fan.
In 1925 the first radio broadcast station in Shibaura, Tokyo has open, and radio wason the trail of huge success, and situation of our vacuum tube factory was out ofdescription. Our effort of tube production, day and night, could never fulfill demand,２and never caught up such a demand even building new facility, etc.
Shortly after that, appearance of tubes for A.C. power supply was a big event.

b. Appearance of A.C. RadioAs the first interest when the radio broadcast has started was popularize radio togeneral public i.e. increasing number of radio sets regardless of crystal or tube model ,and therefore, crystal sets were more popular as of lower cost, but gradually, demandof tube radio was increased, and therefore demand for tubes have greatly increased.
But in the beginning, tube radio needed battery which is extremely inconvenient forhandling , and gave general impression as “radio is troublesome and easily breakable
thing”.
Soon afterward, a research has conducted to use household A.C. power line inEurope, and as the result, tubes for A.C. power line were developed. In our company,
the same research has carried out, and in September 1928, UX-112A with oxide-coatedfilament was made, and in December of the same year, UX-226 has followed. And in
February of 1929, first rectifier tube KX-112A and in October in the same year, firstindirect-heated tube UY-227 has introduced, and finally, radios became operable with
A.C. power line.
About this time, our company has set a firm policy as radio should only be
popularized by A.C. power operated, planned lecture/presentation events and publisheddocuments for general public emphasizing advantage of A.C. powered radio.
We believe that the major reason for present-day success of radio is greatly owing
to realization of tubes for A.C. operation.

c.

Advent of Multi-Electrode Tubes
The improvement of radio has never ended, and A.C. operated tubes keep progress,３and finally, age of multi-electrode tubes has arrived. In 1930 a screen-grid type tube
UY-224 which demonstrates a great performance in high-frequency amplifier was
introduced as a forerunner of tetrode tube, thus most of household radio used screengrid tetrode, and seemed bringing its height of glory together with indirectly heatedtube as detector.
However, there was a drawback in ordinary tetrode tube which creates modulation
distortion, cross-modulation, etc. in some situation, and variable-mu tube was designed
as a solution. In 1932 UY-235 has marketed for the purpose.
In the other hand, the output tube available up to that time was only triodes, but as
higher powered tube was demanded, so-called Pentode which has output sensitivity of
30 times higher than triode, UY-247 has introduced. And then a smaller version named
UY-47B has followed, and next year, high-frequency amplifier tube UZ-57 and UZ-58
replacing UY-224 and UY-235 were marketed. Audio amplifier showed tremendous
improvement by them because only one stage of audio amplifier gave sufficient volume
and sensitivity as it needed two stages before.
Also a new technology made smaller and more rigid tubes possible which was a
result of introduction of smaller ST styled bulb and use of mica spacer.
In other hand, demand of tube for high powered class-B amplifier has created, andUY-46 to suit the purpose has marketed.
And this time, answering demand for much less voltage variation for such highPowered equipment, mercury vapor rectifier tube HX-82 has introduced for use with
UY-46. And further, a larger version, UX-83, has marketed and welcomed by the users.
At the end of 1933, power amplifier pentode UZ-43 and rectifier KZ-25Z5 wereintroduced and made so-called transformer-less receiver possible.

d. Popularization of Radio and Receiving Tubes
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In the history of vacuum tube production and advancement, we hardly note betteryear than 1934. In this year, UX-12A, UX-26B, UY-27A, UY-24B, UY-47B, etc. weremarketed, and as a rectifier, KX-12B has introduced. They have replaced older UX112A, UX-226, UY-227, UY-224, UY-247B and KX-112B with new and smaller ST
styled glass bulb, gained more rugged construction by using mica, and played an
important role for smaller sized and more popularized radio possible.
Also, the filament voltage of older tubes were mainly 2.5 volt, but 6.3 volt model has
gradually adopted in Japan, too. Ut-6A7 was one of the many examples.
Looking at the recently designed tubes, you may notice that many of them show
higher efficiency i.e. one tube serves more than 2 purposes, triode and pentode show
higher efficiency than earlier types, and one tube contains more than 2 units such as
twin-diode/triode, twin-diode/pentode, etc.

e. Recent Battery Tubes

Although battery tubes looked as if all disappeared as a result of introduction of A.C.
operated tubes, but still various progress was shown in this field, too. One example isfor military application like airplane use, etc. and showing unusual progress, but its
detail will not be described here.
From about 1932, demand for battery operated radio is revived, and therefore new
type of tubes have appeared again. They are for use in areas where A.C. power is notavailable, or for portable radio. For those purposes, so-called economical type wasdemanded instead of old and high power consumption types. We have manufactured
the following types for the purpose:
UX-109 (Feb., 1932), UX-110 (Apr., 1933), UX-230 (Nov., 1931), UX-232 (Nov., 1931)
and UX-233 (Apr., 1932).
Among them, UX-109 (triode for det./amp.) and UX-110 (power amp.) are for
operation with dry battery for both A and B source, and filament operates at 1.0 through５

1.3 V, and they are also low battery consumption.
UX-230 , UX-232 and UX-233 tubes are for battery set operable in the area where
no power line is available during daytime, and therefore contributed for popularizing
use in this purpose. This type of battery sets are for storage battery operation, andrecharge after use is required, and therefore 2V of filament voltage is adopted.

3) Recent Receiving Tubes

It should be noted that recent progress in radio receiver is largely owing toinnovation of small-sized multi-electrode tubes. However, not only them, diodes andtriodes are also showing big improvement, and desired tubes having high conductancewith relatively small filament power are available.
We are unable to ignore presence of all-metal tubes although there may not beessential to domestic market. Also transformer-less receiver may become popular as
it consumes less power which matches our national policy, and therefore many new
type of tubes have marketed. We will overview recent receiving tubes:

Diode Tubes

Diode tubes are mainly used for rectifier of A.C. power or detector. For detector,
many types are combined with amplifier tube. Typical diode tubes are: KX-5Z3, KX12F, 12X-K1, 24Z-K2, KX-80, HX-82, HX-83, KY-84 (for rectifier), and Kt-6H6A (fordetector).

Triode Tubes

As early types of triode were for general purpose, and mutual conductance was low.
６But they were improved recently, and development for both voltage and power amplifiertubes were advanced, and mutual conductance value reaches 1 to several milli-mho
level. They are in one way born to compensate drawback of multi-electrode tubes, andfor example, UX-2A3, a power amplifier triode, exhibits excellent performance at theoperating condition as μ: 4.2, rp: 800Ω & Gm: 5.25mS. And UY-6301 suited for
microphone amplifier shows 7.7mS of Gm at 9mA of plate current, 100 of μ and 13kΩof rp, and low noise.
Class-B amplifier tubes are normally used without bias, and therefore need to havehigh μ, but in this case, push-pull connection is required, and therefore twin triode
tubes in one bulb are marketed.
The representative triodes are: UX-2A3 (power amp.), UX-12A (audio amp.), UX-30(detect, amp., osc.), UX-45 (power amp.), UY-56/ UY-76 (detect, amp. & osc.), UZ-19(power amp.), UT-6A6/ UT-53 (class-B amp.), UY-6301 (low-noise/ high-gain amp.),etc..

Tetrode Tubes

Tetrode tube consists of space-charge grid type, screen-grid type, variable μ type and2 grid type for power amplifier.
The space-charge grid type does not seem to show progress except special application
like measuring extra-low input signal, and for portable receiver. This is because recent
triode exhibits progress in design and higher Gm at low anode voltage became possible.
The screen-grid type tetrode has gradually replaced to pentode as a characteristic
disadvantage due to secondary emission.
There are still some tetrode tubes in the market such as: UY-24B (H.F. amp., det.
& A. F. amp.), UX-32 (H.F. amp. & det.), UY-46 (power amp.), UX-111 (det. & A.F. amp.)
etc., and especially UX-111B is designed for dry battery operation, and therefore
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best suited for portable receiver.

Beam Power Amplifiers

The tetrode tube was considered unsuited for power amplifier as it has a drawback
due to secondary emission, and therefore range of usable anode voltage is limited, but
owing to innovation in engineering, it was found that secondary electron emission canbe suppressed without suppressor grid, and beam power amplifier has born as ahighlight of recent small tube development.
In the beam power amplifier, screen-grid current is minimized by matching control
and screen grid pitch toward flow of electron. And also electric potential between
screen-grid and anode become more uniform than pentode, shoulder on the anodecharacteristic curve becomes more steep which results in better voltage utilization ofanode, and also less amount of

third-order harmonics is expected.

Pentode Tubes

The pentode tube was first designed for power amplifier, and then this concept has
adopted to H. F. amplifier i.e. as screen-grid pentode and variable μ pentode.
Pentode tube surpasses tetrode type for higher rp and lower capacitance between
anode and control grid.
By recent development of television, demand of high Gm pentode arose. For thispurpose, UZ-6302 has introduced with a surprising Gm of 10millimho at 12mA of anodecurrent.
The power amplifier pentode tend to show higher third-harmonics compared withthe triode, but requires much lower input voltage, and therefore gives great advantage
in receiver design.
８The typical pentodes are: UZ-2A5 (power amp.), UY-33 (power amp.), UZ-42 (poweramp.), UY-47B (power amp.), UZ-57 (H.F. & L.F. amp., det.), UZ-58 (H.F. var. μ amp.),
UZ-77 (H.F. & L.F., det.), UZ-78 (H.F. var. μ amp.), UY-133 (power amp.), UX-134 (H.F.
amp.), UZ-6302 (TV amp.), etc.

Heptode Tubes

The heptode tube has 5 grids between cathode and anode, and is used as the firstdetector (frequency converter) in the super heterodyne receiver. There are Ut-2A7, and
Ut-6A7, etc. as example.
The 1st and 2nd grids form local oscillator circuit. Electrons generated from cathodeis modulated by the local oscillation frequency and reaches 3rd (acceleration) grid, but
as 4th grid is at a negative potential, forms space-charge layer and create fictitious
cathode, and electron exited from it is further modulated by 4th grid (by input signal),
and finally accelerated by 5th grid and reaches anode. Thus anode current contains
intermediate frequency component proportional to variation in input signal and local
oscillation frequency.
Namely, heptode operates at no-load, its oscillation activity is stable and have highconversion conductance, but the other hand, high harmonics in the output and highnoise level are its negative side.
Ut-2A7, Ut-6A7, UZ-1C6B (for battery operation), etc. are examples of frequency
converter tubes.

Triode/ Pentodes

These are types that one each of triode and pentode unit contained in a glass bulb,
and the typical example, Ut-6F7 can be used in super heterodyne receiver as local
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oscillator and first detector with one tube.
In this group, we also have our own type of tubes.

Twin-Diode/ Triodes

This type consists of a pair of diode and a triode, and use the former as detector, andthe latter as amplifier. Typical products in this category are UZ-2A6, UZ-55, UZ-75 andUZ-85. They all place a triode unit at the top and diodes at the bottom (in a shieldedcompartment) of a common cathode.

Twin-Diode/ PentodesThis is the type replacing triode in the type described above with a pentode, and Ut2B7 and Ut-6B7 are the typical examples. Usage of them has no big difference between
Twin-diode/ triodes; use diodes as detector and feed its output to audio amplifier; use
one each of diodes for detection and AVC; make only one tube for I.F. amp., detection
and audio amp.,
etc.

All-Metal Tubes

The receiving tubes in our country reached a turning point at 1933, and as a result,smaller size and shock-free construction with ST bulb were realized, and after 193334, this trend has continued.
But about this time, there was a surprising fact occurred i.e. introduction of Catkintube in UK. The concept of Catkin tube was differed tremendously because of using
metal around glass envelope. It was sufficient to catch curiosity of people, but as it was
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just placed anode outside the glass, and considered insufficient for defining as
unbreakable, and although recognizing its advantage, still had to be rated as atransient product.
In our laboratory, we saw this as an important matter, and R & D project was inprogress. And recently, the effort led to production of all-metal tube. This success mustbe evaluated as a conclusive result towards smaller and more rugged construction inprogress of receiving tubes.
The construction of this type of tube is totally different from existing types. Using
steel envelope instead of glass bulb, and it works as perfect shield at the same time,
and therefore capacitance between grid and anode is reduced tremendously. Also shapeof stem has totally changed, and lead wires have brought outside through eyelets
consist of special metal called fernico and special glass having identical thermal
expansion coefficient as fernico. This construction maintains vacuum seal perfectly.
By these features, realization of many advantages have resulted as follows, andmade future of all-metal tube delighted:a): excellent and uniform electric performance,b): rugged construction maintains performance against shock,c): smaller size,d): suited for short wave application because of low internal capacitanceAt the present, all-metal tubes produced by us are as follows, and the day in whichthese tubes appear in the marketplace under the name of Mazda should not be too longin a future:
US-6C5 (triode), US-6J7 (H.F. pentode), US-6K7 (variable-μ pentode), US-6F6(power pentode), US-6H6 (twin diode), US-6L7 (mixer), US-6V6 (beam power tube), etc.
Tubes for Transformer-less Receiver

It was several years ago when so-called transformer-less tubes which do not need
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transformer have introduced in U.S. The reason why it did not get popularity in Japan
at that time was because low cost power transformer was readily available. But asmaterials became in short supply and controlled by the government because of war in
China, it became very important to save precious material like copper and iron, anddemand of transformer-less tubes became essential, and production of new tubes haveaccelerated.
The transformer-less tubes are not different in their operation like amplification,
detection, rectification, etc., but only make their filaments connected in series, and heatthem directly from 100V A.C. supply without using transformer. The heating current
selected in this case was 150mA.
The existing tubes can be used for this purpose if filament current rating is identical,
and in fact in U.S., such receivers are manufactured with existing tubes having 0.3A ofheater rating. In this idea, no new type of tubes are required, but instead, it requires
30W of electric power regardless of actual need. This seems out of question in the city
areas, but in rural areas where power consumption of less than 20W was desired forlisteners because of fixed-rate power cost.
As to output power, it is desired to have minimum of 0.25W for household set. It
may be said the higher power the better, but considering use of a popular magnetic typeof speaker, more than 1W of power should not be necessary.
For these consideration, our Mazda receiving tubes for transformer-less receiver
has designed as having total power consumption of less than 20W, and their filament
voltage is rated as 12V or twice of it. Following is the list of such tubes:
12Y-V1 (H.F. variable- μ pentode)
12Y-R1 (H.F. amp. & detector pentode)
12Z-P1 (power amp. pentode)
24Z-K2 (voltage- doubler rectifier)Note: these type numbers and ratings were certified by Japan Broadcast Society as a
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standard of transformer-less receiver, and the first letter (s) indicates heater
voltage, the second letter shows type of base, the third means kind of tube or
usage, and the fourth shows order of manufacture. But for rectifier, the fourth
letter means: odd number as half- wave type, and even number as full- wave or
voltage- doubler type.

Pliotron Audion
Earliest TEC vacuum tubes
UV-199 UV-200 UV-201 UV-201A
Tubes used when radio broadcast started

Above:
Receiving Tube Production in TEC
Solid line: No. of tubes sold
Dotted line: No. of workers
Below:
No. of Radio Listeners

Horizontal axis: Year 1925 to 1939
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Comparison of newer (left) and older (right) types in typical receiving tubes

Left: UX-12A andUX-112A
Right: UX-26B and
UX-226

Left: KX-12F and
KX-112A

Right: UY-27A andUY-227

Left: UY-24B andUY-224Right: UY-47B andUY-247B

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Example of Receiving Tubes:

Part 1

１５

Example of Receiving Tubes:

Part 2

１６

Example of Receiving Tubes:

US-6F6

US-6J7

Example of Receiving Tubes:

12Y-R1

Part 3 (Metal Tube)

US-6J5

US-6C5

US-6H6

Part 4 (Transformer- Less Tube)

12Y-V1

12Z-P1
１７

12X-K1

24Z-K2