February 1933 Radio-Craft
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles
Here is a vacuum tube chart everybody needs. Well, not really, but
surely somebody out there in the RF Cafe audience will find it useful.
By 'audience' I mean most likely a hobbyist who is restoring or
repairing a vintage tube-type radio, television, piece of test equipment,
etc., and has never even heard of RF Cafe, but finds exactly what
he (or she) needs as the result of
a Google (Bing, Yahoo, whatever) search.
If it seems like you can find information on just about anything
you need on the Internet these days, it is at last partly because
of efforts like mine that uses a LOT of personal time and some personal
funds to establish and perpetuate the reality. Others of you contribute
in different ways; this is mine. A helpful way to make it worthwhile
is to visit websites of companies that advertise on RF Cafe. A lot
of great products and services are offered, and it doesn't cost
you a penny to investigate. Thanks.
Tube Characteristics & Data Chart
Francisco Pinto Basto*
Fig. 1 - Tube Data Chart
A graphic representation of the following factors of
tubes: amplification factor, mutual conductance, plate resistance,
power output in milliwatts, power output in decibels, and
R.F. performance factor. Forthcoming tube characteristics
may be interpolated as the data becomes available. This
procedure is discussed on the preceding page, and in the
August, 1932 issue of Radio-Craft.
In reference to the article of Mr. C. H. W. Nason. entitled "Tube
Characteristics at a Glance." published in the August issue of your
journal. insert page 128A. I would like to submit to Radio-Craft
a handy. graphic chart for tube characteristics. I have never seen
such graph in any paper; only in the "Telefunken Zeitung," April,
1930 is shown together with the triangular chart another graph employing
log-log paper, where the penetration factors
(in German-Durchgriff - 1/mu) are marked as abscissae and
the resistances as ordinates, and the mutual conductances are given
by a 45° lines net.
In my chart. Fig. 1. a log-log paper is also used. As abscissae
(A) are marked the amplification factors and as ordinates (B) the
mutual conductances in mA per volt. The A. C. resistances are given
in kΩ by a family of straight lines (C) easy to construct.
For better comparison of power tubes. another family of 45°
lines, perpendicular to the former, may be drawn. These lines (D)
will give the maximum power output per peak volt squared input that
a tube can deliver:
To avoid a complexity of lines, only the lines for 1, 10 and
100 milliwatts per square volts (peak) are set up. The power subdivisions
P may be read on a resistance line, say, on the 1 kΩ line.
Together with the milliwatts scale is inscribed a decibels scale
(E) having the 0 level in 1 milliwatt per square volt, but any other
level may be used.
Any tube is represented by a point which gives at a glance the
three parameters: mu, mutual conductance, and resistance.
Now, suppose that we wish to compare two power triodes, for instance.
the '10 and the '50. The graph shows (dotted) that the '10 gives
5 decibels above the level and the '50 3 decibels. It is to be noted
that a triode gives 0.4 - to 0.8 - decibel less if the undistorted
output is considered because the load is twice or three times the
A. C. resistance. Without great error we can assume a 0.5-db. loss
for all the triodes; consequently it may be taken into account merely
the decibels difference of the two tubes and we say that the '10
gives 2 decibels more per square volt input than the '50. If the
largest input voltage to be handled is low enough not to overload
the '10. this tube will be preferable to the '50.
For identical power pentodes this simple comparison may be made,
but if we compare a triode and a pentode, a deduction of 2 (to 4)
db. must be made from the pentode's power, due to the fact that
the pentode requires a load 5 (to 11) times less than the A. C.
resistance. By this means the graph indicates for the '47 (deducting
2 db.) 13 db undistorted output more than for the '45. for the same
Another family of 45° lines, perpendicular to the resistance
lines' may be constructed, giving the R. F. Performance Factors:
the scale (F) R. F. P. F. is plotted on the 10 kΩ line.
In radio frequency. it is well-known that the maximum voltage
gain obtainable with a tube followed by a suitable transformer is
provided that the turns ratio of the transformer is properly
is the dynamic resistance of the coil and Rp the A. C.
resistance of the tube, w and r being respectively the inductive
reactance and the radio frequency resistance of the coil.
Hence, factor F may give a fair idea of the maximum voltage gain
that we can obtain with an R. F. transformer coupled tube.
A little investigation shows readily that the decibels scale may
be used to give a computation of the gain obtainable with a given
radio frequency tube.
If G. is the voltage gain, the decibels gain is given by db =
20 log G = 10 log G2 =
As the decibels scale divisions are proportional to log
may be used also for this case.
The power lines may be plotted also in the triangular chart,
referred to in the August issue, but it will be very laborious work.
Other charts employing log-log paper may be constructed, for
instance, with mu, as abscissae and Rp as ordinates.
Posted March 10, 2015