(002W)

On some Home-made Triodes
By Dr. Hidetsugu Yagi
Abstract
This is the report of tests of some home-made triode vacuum tubes, carried out
in the Tohoku Imperial University about eighteen months ago.
The static characteristics are first given, from which the operational constants
such as “Mutual Conductance”, “Amplification Constant” etc. are derived.
After reviewing the behavior of the different types of tubes, some essential
points are brought out about their design.
How the mutual conductance varies with the filament heating is thenexperimentally studied. The “Lumped Characteristics” of two entirely different
kinds of triodes are plotted, as suggested by Prof. Eccles.
The photograph of the triodes under test is reproduced.
When author conducted research on the wireless communication by receiving science
research subsidy from the government, a chance had given by collecting domestic triode
tubes and test their characteristics as foreign specimens were hard to obtain. The results
have suggested that some promising points exist although there seems some limitation in
their manufacturing skills. As we realize that there must be big progress carried on therecent foreign technology and problem solving skill, reporting results of this test series may
not be useful, but have decided to report it as there may have value to some people. Since
these tests were conducted mainly from the year 1919 through spring of 1920, and therefore
ask readers allowing us to somewhat outdated and insufficient results.
There were only five factories from which the specimens we have tested this time weresupplied, and only two factories in them were manufacturing Pliotron*1 and Oscillion*2 typetubes for oscillation, and all others were manufacturing only small tubs which are in thesame category of Audion*3. Moreover, one of the Pliotrons supplied this time was failed togive an acceptable result, and had to be excluded from this report. Therefore there was only
one product reported here as Pliotron.
*1: Pliotron is a trade name of Transmitting Tube by G.E., U.S.A.
*2: Oscillion is a trade name of Transmitting Tube by deforest, U.S.A.
*3: Audion is a trade name of Receiving Tube by DeForest, U.S.A. ------ Ed.
1

At first, tested static characteristicsby keeping plate voltage constant (invarious value) with the connection
diagram as shown in Fig.1. From thesetests, curves were obtained as in Fig. 2,and from them mutual conductance*4
canbeconductancedetermined.

Mutualequalsagainstslope

horizontal line.
Next is amplification constant (orFig.1: Test Circuit

voltage amplification)*5. This is defined
graphically as Eccles described in RadioReview.
*4: Now known as μ
*5: Now known as Gm ------ Ed.
In Fig.2, draw arbitrary horizontal line
PQRS, then draw vertical line po, p, qo, q, etc.,
and make their length proportional to plate
voltages. And draw a straight line nearest to p,q,etc. and let it reach the horizontal line. AsPQRS is a straight line with constant plate
current, (Ep + kEg) is constant. Therefore whenFig.2: Typical Curves obtained

Ep has changed, kEg compensate the variation.
Therefore slope of the line pq--- should showk (Refer to p.74, Vol.1, No.2: Radio Review, Nov.,
1919).

The value of k (amplification constant) determined by static characteristics is expressed
as a function of plate current. When mutual conductance μ and amplification constant k aredetermined, internal impedance R can be calculated as: R = k / μ. But here, μ is expressed
as a function of grid voltage Eg with plate voltage Ep as parameter, and k is simply a functionof plate current Ip. Therefore not easy to determine R. As to these three constants, refer toTohoku University Report.
In order to determine right values in filament current, plate voltage Ep and grid voltage
Eg for the tubes gathered here are somewhat difficult. As described below, in case of Audion2

in general, static characteristic curve indicates convex against horizontal line, and when Eg
has changed from negative to zero, form of saturation rarely appear. However, some Pliotron
already show saturation in Ip when Eg is still negative. From this observation, it seems thatfilament heating may be too much for Audion, and insufficient for Pliotron. But this may
not be avoidable. In case of Audion, it is impossible to raise Ep much as it has low vacuum.
Namely, high level of thermion is obtained as filament heating is sufficient, but as Ep is solow, and therefore never saturates. But in case of Pliotron, Ep can be much higher as its
vacuum level is very high, but having relatively narrow distance between electrodes, andtherefore describe a result for tendency of saturate even filament generates high thermion.
Therefore Pliotron shows maximum value in mutual conductance (refer to point of inflection
in static characteristics). Many Audions show no point of inflection and therefore nomaximum point in mutual conductance. Even in case of Audion, similar curves will beobtained as in Pliotron if filament heating is insufficient.
Total number of tubes we tested this time reached 50-60, but few pieces in eachcategories are picked up here, and characteristic curves are shown and explanation addedfor 16 selected specimens. And lastly, we intend to describe a result for influence of filamentheating, and so-called Lumped Characteristics.
Pliotron: “T” Company: Tubular- #2, Spherical- #a
Audion: “T”

Company: Type A- #b / #e, Type F- #b / #d“N.M.” Company: Tubular- #La / #Lb“A”

Company: Type- #p / #s / #c / #r“O”

Company: Spherical- #b / #d“J.N.” Company: Spherical- #a / #b
Note: a.: The company names assumed are: “T” as TEC, “N.M.” as Nihon Musen (JRC), “A”
as Annaka??, “O” as Oki??, and “J.N.” not sure.
b: We guess that there was a trend in Japan at that time not to disclose a specificproduct and/or name of the company who made it, but it is quite regretful matter tous. Frankly, this report does not have much value without tube types and supplier’snames, but editor decided to report here because it was one of the earliest reports
in this category, specially referred in the first document (001W), and the author wasDr. H. Yagi, famous as inventor of Yagi Antenna. ----- Ed.

3

Pliotron (“T” Co., Tubular- #2)
This tube shows quite satisfactory results as oscillator. As its filament issurrounded by grid, amplification constant shows large value as 14. Vacuum levelis good, and no grid current flows at Eg < 0. It suggests good design andmanufacture. It is unknown if it is still good when higher voltage than 700V andmuch higher power output is required as we could not test this time.

Fig. 3a: “T” Co.- Pliotron, Tubular- #2

Fig.3b: “T” Co.- Pliotron, Tubular- #2

Pliotron (“T” Co., Spherical- #a)
This specimen looked also
good, but sufficient result could
not be obtained as there was alimitation in plate battery.

Fig. 4: “T” Co- Pliotron, Spherical- #a4

Audion (“T” Co., Type A- #b & e)Note: High vacuum version of Spherical Audion by TEC? --- Ed.

So-called U.S. type and have only 5 in k value. The sample #b has maximum
point in μ, and this may be caused by current diverted to grid rather than shortageof filament heating. Tubes of type A are generally uniform in quality, having small
k value and Ip is hardly reaching zero when Eg gets negative. It is preferable to bein high reliability, but in case of receiving tube, there are product of less reliable,
but having higher sensitivity.
We are always obtaining satisfactory results by generating oscillation withstable specimens.

Fig. 5a: “T” Co.- Audion, Type A- #bFig. 5b: “T” Co.- Audion, Type A- #bFig. 6a: “T” Co.- Audion, Type A- #eFig. 6b: “T” Co.- Audion, Type A- #e5

Audion (“T” Co., Type F, #b & d)Note: May be UF-101 by TEC ----- Ed.

Called French type. Filament is surrounded by cylindrical grid, and therefore
large amplification of k value (13-15) is obtained. As 0.6 Ampere of filament current
has passed, curve of μ is bent as in the graph. If filament current gets higher, theμ curve should bend reversed (refer to “O” Co.’s product described later), but as
their filament looks fragile, we assumed that this may be a limit. Looking fromcharacteristic curves, it is obvious that the French type is more superior.

Fig. 7a: “T” Co.- French Type- #b

Fig. 7b: “T” Co.- French Type- #b

Fig. 8a: “T” Co.- French Type- #dFig. 8b: “T” Co.- French Type- #d6

Audion (“N.M.” Co.- Tubular- #a & b)

Note: Maybe C1 or C2 by JRC ---- Ed.

Many of this type have large amplification constant k (like over 20) because of
tubular shape, but vacuum level is found very low and poor uniformity between
each product. But some of them show unusually high receiving sensitivity incertain conditions.
This type is hardly usable for oscillation as it is too easy to generate glow, andtherefore be limited to receiver use. But it tends to generate self-oscillation even in
the receiving equipment as it is operated near glowing condition. As obvious fromthe test results, its characteristic curves are not smooth, and grid current appears
early which confirms that it is not pure electron discharge. When Eg is positive, iteasily generates ion bombardment which cause glow, and mutual conductancecurve deforms vigorously. At near Eg = 0, detecting sensitivity tends to gets
extremely high, and show much superior sensitivity over other high-vacuum
products like “T” Co.’s type A. Therefore it seems good sensitivity does not always
satisfy reliable products too.
This company’s new product looks similar to French type, but level of vacuum
and other parameters are similar to the above product. We assume that this isbecause of incomplete vacuum system they use which is shame, but similar
situation may be seen in other companies. For example, Moorhead Audions whichis marketed by DeForest for amateur use show fairly good sensitivity, but seems
having inferior vacuum which may be appealing to amateur users.

Fig. 9a: “N.M.” Co.- Audion, Tubular- #a

7

Fig. 9b: “N.M. Co.- Audion, Tubular- #a

Fig. 10a: “N.M.” Co.- Audion, Tubular- #b

Fig. 10b: “N.M.” Co.-Audion, Tubular- #b

Audion (“A” Co.- #p)
This product has a unique construction. Both grid and plate consist of Tungsten
wire wrapped around square jig. We are unable to evaluate merit and/or demeritof wired plate, but test results suggested that this tube is far superior to ordinary
Audions for oscillation as they claim. As its vacuum level is extremely high, it could
be used up to 400V of plate voltage although outer diameter is only 6cm. We rate
this tube as good for oscillation as Pliotron.

Fig. 11: “A” Co.- Audion- #p8Audion (“A” Co.- #s)
This is a small version of #p, and found as Audion with low vacuum. The reasonfor having high amplification factor (20 toward 40 for higher Eg) may be because ofwired plate rather than that of ordinary sheet metal. It seems that higher
amplification constant may be obtained
when both grid and plate are wired. Thissubject must be calculated as a problemof

staticfield,

but

Germanword“Durchgriff” has deep meaning, and in
this case, k value appears larger as
durchgriff of plate against filament issmall. Therefore large k value does notalways mean good tube

Fig. 12: “A” Co.- Audion- #s

Audion (“A” Co.- #c)
Plate is cylindrical shape
as in French type, and k value
exceeds 20. As grid pitch isfine, durchgriff is small as in#s.

Fig. 13: “A” Co.- Audion- #c
9

Audion (“A” Co.- #r)
Plate is a circular disc at the top,
grid in the middle and filament at thebottom,

andspace

betweeneach

electrode is not narrow. Therefore plate
current could not be minimum evenwith negative Eg. Although k value
reaches 20, we are unable to say that
this tube is a successful sample.
As a conclusion for evaluating tubes
by “A” Co., first #p type is rated as good,
but all of them seem having too small
durchgriff, and suggests that area ofplate and pitch of grid wire must be
important factor for design.
Fig. 14: “A” Co.- Audion- #r

Audion (“O” Co.- Spherical- #b and d)
From external appearance and characteristics, uniformity of products may lookbetter than type A of “T” Co. (early DeForest Audion type), amplification constantranges 11-13 whereas the ones by “T” Co. is around 5. Therefore these specimens
should be evaluated as quite good for ordinary Audion. Recently, French type withlarge amplification are popular, but this company only offered so-called U.S. type.

Fig. 15a: “O” Co.- Audion, Spherical- #b

10

Fig. 15b: “O” Co.- Audion, Spherical- #b

Audion (“J.N.” Co.- Spherical, #a and b)
Thiscompany

offeredfairlyprecisePliotron, but regret that we could not list here
because of inferior record. For old U.S. type
Audion, the results as indicated here wereobtained. These specimens seem taking very
long time after their production, and therefore
having slightly lower vacuum level. Theirfilament required more than 2A, and shownsmall amplification which must be points toimprove. In these points, the ones by “O” Co.
are better. But note that the ones making
record in receiving sensitivity are with lower
vacuum, easy to generate glow like tubular
Fig.16: “O” Co.- Audion, Spherical- #dtype, French type, etc. rather than U.S.typewith high vacuum as described in tubular“N.M.” type.

Fig. 17 (“J.N.” Co.- Audion, Spherical- #a)11

Fig. 18a: “J.N.” Co.- Audion, Spherical- #b Fig. 18b: “J.N.” Co.- Audion, Spherical- #b

Characteristics varies against filament temperature
We have conducted special tests finding out variation in tube characteristics
against filament temperature. The result were shown in Fig.19. From this,calculated mutual conductance as Fig.20. The point for maximum μ shifts towardright hand side when filament temperature gets higher, and when it gets to low
and unable to produce sufficient thermion, then the curve quickly saturates andmutual conductance become lower, and therefore maximum value of μ occurs at amuch lower value.

Fig. 19: Filament Temperature

Fig. 20: Mutual Conductancevs. Filament Current

vs. Filament Current

12Lumped Characteristic
According to Prof. Eccles, plate current Ip is a function of plate voltage Ep andgrid voltage Eg, and can be expressed as a function of (Ep + kEg), and therefore
when express this (Ep + kEg) as El, and name this as Lumped Voltage, Ip can be
expressed as:Ip = f (El)As already shown in Fig.1, when a group of characteristic curves are given, thenamplification factor k can be determined. And next, calculate El namely (Ep + kEg)
on each point of characteristic curve, and make a graph of the relation between Ipand El. The resultant characteristic curves concentrate into an almost single line.
Prof. Eccles named this single curve as Lumped Characteristic against certain
filament current. It is said that straight portion of the curves match well, and only
areas near saturation do not match.
In order to express characteristics of a given tube it is adequate to do it with agroup of curves, and trial for attempt to show it with single curve like lumped
characteristic may not be useless because it makes rather hard to realize as Prof.
Howe pointed out earlier at the discussion held in Physical Society of London, it isessential to actually try if lumped characteristic made by many characteristic
curves can be matched.
The author plotted many characteristic curves with vacuum tubes as describedabove, tried to draw few lumped characteristic curves.
Fig.21 shows relation between lumped voltage El and plate current Ip with

Fig.21: Lumped Voltage El for French #d13

k = 13 on French #d tube, and confirm that the curve between 20 and 45V of Ep isquite well matched.

Fig. 22: Lumped Characteristics for “T” Co.- Pliotron, Tubular- #A

Fig.22 shows lumped characteristic between 100V and 400V of Pliotron tubular#A, and verifies that it matches well in the middle, and show separation at the bothends.
Looking from those results, lumped characteristic seems not much of practicalvalue exist, but can be found that it is reasonably accurate to make Ip as a functionof (Ep + kEg), and at the both ends of curves, it should need adding another constantlike e to match actual situation as:
Ip = f (Ep + kEg + e)
(if keeping k value constant).

The author expresses his sincere appreciation to each tube manufacturer which supplied
vacuum tubes for this series of tests, and gave convenience to the author’s research work.
And also express appreciation to my assistant, Zenroku Hanzawa.
14

Triode Vacuum Tubes used for this series of test

On some Home-made Triode: by Dr. Hidetsugu Yagi, p.p. 497-511, IEEJ
Bulletin (DENKI GAKKAI ZASSHI) Vol.4, No. 396 (1921)

15