February 1933 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
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/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 grid swing.
Another family of 45° lines, perpendicular to the resistance lines' may be
constructed, giving the R. F. Performance Factors:
F = ; only 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 given by
provided that the turns ratio of the transformer is properly adjusted where 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
As the decibels scale divisions are proportional to log ,it may be used also for
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 September 21, 2022
(updated from original post on 3/10/2015)