(007W)

Conclusion: Dawn of Tube Production in JapanBy H. Ohtsuka

As everybody knows, Japan was a late comer for vacuum tube development comparedwith western countries. Therefore first production of Spherical Audion was approximately
10 year behind in Japan. But fortunately, TEC (changed company name to Toshiba in 1939)
had a family tie between GE (and RCA), and NEC was associated with Western Electric(and STC). Therefore, once started development program, they picked up its essence quickly,
and made their copies first. JRC, another forerunner in Japan, started work by himself first,
but a little later, showed influence from Telefunken which he was associated with.
For that reason, it is only natural to see that majority of our early products wereequivalent or similar to those of our teachers.
Look at table (015L) included here. This table was made by an idea of editor trying tocompare how Japanese tube industry followed up U.S. and European tube development
trail. As it is impossible to list all tubes developed in each year, picked up only
representative ones forming one line in the particular year. Although it is difficult tovisualize the whole situation, it may give you some idea for how Japanese tube production
has chased U.S. and European development.
You can see that it became considerably shorter. For example, production of UV-200 /201 was 3 year behind U.S. If you compare it with Spherical Audion’s case which took about
10 years as described above. It may suggest that Japan’s speed catching up new technology
at that time.
You may also notice that many, if not the most, of our products bear similar type numbers
which you can easily find their sources, mainly U.S.
Please find some photo copies in (001P) which we have on display at UEC (University ofElectro-Communications) museum in Tokyo. We must admit that there are relatively few
specimens here mainly because of the editor who is practically managing old tube sectionin our museum was out of country for too many years, and when he came back to his homecountry, majority of good items were already gone. Here, we must admit weakness
particularly in transmitting tubes, microwave tubes, etc. We have few specimens of them,of course, but decided not to list in this report.
Talking about transmitting tubes, editor was quite surprised that NEC had a uniquestart in developing them. Most companies in the world started producing transmitting tubes
from real small ones. But NEC was an exception. He has started tube development a little
late in time, and many people understand that he was specialized in wired telephone tubes
1like WE’s 101, 102 and 104 series. But actually, NEC has started transmitting tube
development from large water-cooled tubes. The first one, TW-504-A (c.1933) was 15kW
output, and the second one, TW-502A (c.1935) had 120kW output. Please find information
on pages 2-4 in (005W).
Editor found an impressive photo of TW-502A (page 11 of same literature), but could not
find similar one like this double-ended water-cooled tube anywhere. Wonder if he had apartner in the world at that time? WE does not list such a tube (according to “75 Years ofWestern Electric Tube Manufacturing” by B. Magers, etc.). Maybe STC in U.K. gave theirknow-how in this area.
Going back to the photo copies (001P), you may notice that there are a series of RCA type
metal tube made by Toshiba, and few by NEC. The Toshiba models are in the oldest style ofRCA types, but editor wonders how Toshiba secured special machinery necessary formanufacturing them. It was 1935 when RCA announced its introduction, and the outbreakof war in Pacific Ocean was in 1941, only 6 years in between.
Among WW II tubes Toshiba has produced, Sola (means sky) and Umi (means sea) may
be of your interest. The former, similar to 12SJ7GT (MG), was a standard sharp-cutoff
pentode, but Toshiba could not produce big volume of button stem at that time, andtherefore had to use pinch stem instead. At that time, Dr. E. Nishibori hinted applying a
conductive coating (like aquadag) on the surface of stem for reducing capacitance between
G1 and anode. And Sola was designed so that even untrained women can assemble them,and from geisha girls to noble ladies worked in the factory or even in their home. At thattime, JRC has introduced FM-2A05A, an improved model of German NF2. It was similar toSola and RH-2 (one of the other series by Toshiba), but had better performance includingmuch lower Cp-g. The Japanese military offices forced to produce them, but JRC could notmeet their huge demand. Therefore other tube makers were forced to assist it, but could not
do well as the tube was too difficult to make. In that situation, Sola was to fill the gap evenwith somewhat inferior performance.
As to Umi, there was a long time rumor for existence of this tube as a pair to Sola, but
actually, nobody knew what it looks like. But last year, multiple specimen were appearedon Japanese internet auction, and editor was lucky enough to get them. It was a directheated diode with a slim coaxial anode, and in fat MT- like bulb with special 3 pins whichis totally against people’s imagination, and can not tell what it was used for. We will
welcome for any information on Umi.
Another samples of metal tube are by NEC. Look at their photo in (001P). MC-804-A is
not well documented, but MB-850 is similar to 6SH7. Their construction looks like WE’sKlystron, etc., and again a question arises for how NEC secured manufacturing machinery2

at that time.
Editor expresses sincere appreciation for his colleagues in UEC’s tube group in finding
source of literature and various assistance. Without their support, this article could never
be completed. Thank Kentaro Aoyama, Koji Maki, Motoaki Tokida and Akio Yamakata.
October, 20163