February 1936 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.
Competition amongst countries and businesses existed long before
the advent of radio receivers. Here is an interesting story
which demonstrates how international politics and corporate
policies has been part of the electronics industry since its
inception. In order to circumvent what were considered to be
outlandish patent licensing fees, Danish engineer Carl Arne
Scheimann Jensen developed a new 'gridless' type of vacuum tube
(aka valve) which was called the
Rather than using a screen grid in the path between the cathode
and plate, the Renode employed two sets of beam concentrator
and deflector plates on either side of the electron beam's path
to modulate the conduction. According to measurements it provided
a slight improvement in both linearity and selectivity. The
article's author hints at the possibility that further manipulations
and back-room deals might eventually scuttle the effort to bring
Renodes to the mass market; given that even finding information
on the Renode is nearly impossible at this time, evidently he
The Renode - A New Gridless Tube
A revolutionary Danish radio receiving tube of "cathode-ray"
type is announced in this exclusive story by our Danish correspondent.
First Published Description!
In this exclusive article Radio-Craft presents the first
description in America of the radically new cathode-ray type
of detector, amplifier and oscillator tube. According to available
data it apparently results in more selective, sensitive, and
noiseless performance than present grid-type tubes! It appears
to rank in importance with the recently-announced (Jan. 1936
issue) Zworykin electron-multiplier "ray"-type tube.
Fig. A - The internal structure of the tube
showing the cathode surrounded by a shield having a slot cut
parallel to its axis; an "intensifier" to speed up the electrons;
two "deflectors" to control the electron stream; and a plate.
Gridless vacuum tubes, in a new series, have just been introduced
in Denmark! Due to a peculiar patent set-up, Denmark has been
subjected to excessive licensing fees, and it is this situation
which the new tubes have been designed to circumvent.
The following technical and political explanation outlines
the characteristics and conditions under which the Renode, as
the new tube is called, has been introduced.
Operates on Cathode-Ray Principle
In principle, the Renode has some resemblance to the Braun
tube, the workings of the former being founded upon deflection
of cathode rays (first utilized in the latter).
The interior arrangement of the electrodes in the Renode
is shown in Fig. 1A. The circle indicates a cross-section view
of heater; and cathode, K. Element C is a metal screen or shield
(hereinafter called the concentrator); it surrounds the cathode,
and has a slit across it parallel with the length of the filament.
Electrode I is an auxiliary plate termed the intensifier; it
is plate-shaped and has in the middle of it a slot of exactly
the same size and position as the one in the cathode screen.
Plates D1 and D2 are called deflectors. The ordinary plate or
"anode" is identified as P.
Now let us proceed to see how this arrangement works, by
referring to Fig. 1B. Potentials are applied to the electrodes
as shown; cathode, and deflecting electrodes D1 and 2 are at
zero voltage; the intensifier, I, and ordinary plate, P, under
a certain positive potential; and the concentrator, C, at a
suitable negative potential (as indicated by [- - -]).
Under such conditions a concentrated, straight-line electron
beam, the outlines of which are defined by the apertures of
the concentrator and intensifier electrodes, will flow across
Fig. B - The appearance of the tube elements.
Controlling the Beam
Now, if the numerical value of the concentrator potential
is decreased (as indicated by [ - - ], in Fig. 1C), the beam
will spread itself out in the middle between the deflectors.
A further decrease of the concentrator potential ( - ], in Fig.
1D) will result in some of the electrons touching the deflectors,
which are thus compelled to receive a certain number of electrons.
When the value of concentrator potential required to bring
the tube functions into the state illustrated at Fig. 1D is
found, the goal of "ordering the cathode ray" to suit a purpose
has been reached. If R.F. currents are now applied to the deflectors,
as shown in Fig. 2A, the beam will be deflected alternately
towards either of the opposite deflector electrodes, which must
again absorb a certain number of electrons varying according
to the deflection. As the beam is "ordered" so that a very insignificant
number of electrons are caught by the deflectors when these
are at zero potentials, an increase of the total number of electrons
caught by the deflectors will practically always result when
an R.F. current is applied.
Fig. 1- The tube action in detail.
The momentary number caught is a function of the rise and
fall (fluctuation) of the R.F. voltage, and condenser C2 will
be charged to a value depending on the momentary value of the
controlling voltage; i.e., the voltage of condenser C2 will
vary according to the modulations of the incoming R.F. voltage.
Besides the R.F. controlling voltages we thus get impressed
on the deflectors a negative potential that numerically varies
with the R.F. modulation. creating in the space between the
deflectors a negative electric field that counteracts the positive
field from the intensifier, and thus permits less electrons
to get through to the plate.
Fig. 2 - The circuit for detector action.
The plate current therefore will vary with the R.F. modulation;
i.e., an increase of the applied R.F. voltage will result in
a decrease of the plate current (or detection).
Since in this arrangement the R.F. voltages on the deflectors
at any time will be numerically equal but of opposite polarity,
it is obvious that none of the R.F. oscillations in the input
circuit will be carried over to the plate or intensifier (auxiliary
plate) circuits. In plainer language: we get rid of those annoying
tendencies to instability in the following A.F. stages, so familiar
with conventional grid-controlled tubes.
The situation is different if we hook the Renode up in a
circuit like that illustrated by Fig. 2B. In this case the R.F.
voltages applied to the deflectors are both equal in value and
polarity, which condition naturally sets up R.F. currents in
the plate and intensifier circuits, varying in concert with
the incoming signals.
In both diagrams the tube works as an "ordered beam"; however,
in hookup A the beam moves brush-like, alternately towards either
deflector plate, while in hookup B the beam "swells" in the
middle, so to speak, and widens out towards the plates, as depicted
in Fig. 1.
With a view to further elucidating the behavior of the Renode
a few characteristic curves drawn by the inventor on the basis
of laboratory experiments are shown.
Figure 3A shows the detector characteristic of the Renode
(A) as compared with an ordinary R.F. pentode (B). The grid
leak in both cases was 2 megs. (The readings on the vertical
axis, left, are for the Renode, those to the right for the pentode;
the units are in centimeters - i.e. readings on a large scale
by means of a mirror-galvanometer - and they indicate relative
values of deflector-currents plotted against input R.F. voltages
at zero per cent modulation. To convert centimeters to inches,
multiply the former by 0.3937.)
Figure 3B shows the total amplification of a Renode (A) as
compared with that of an R.F. pentode (B). Input voltage (abscissa)
in millivolts at 30 per cent modulation is plotted against output
In Fig. 3C, is shown the selectivity curve for a Renode (A)
and a pentode (B) working in identical tuning circuits. For
the sake of clarity both curves are reduced to a peak of 1 V.,
but actually the Renode curve had its peak at 4.6 V., while
the pentode reached only 3.75 V. The two dotted lines denote
values of voltage obtained at a band width of 10 kc. For the
pentode we find a voltage of 0.77-V. but the Renode yields 0.47-V.
or 61 per cent less than that of the pentode. This spells: better
Fig. 3. Comparative characteristics of Renode
and Pentode as a detector.
The Patent Situation
A peculiar condition surrounds the development of the Renode,
as explained below.
Initial experiments on the Renode were started some 5 years
ago by A. Schleimann Jensen, a Danish engineer and radio editor.
When, after 2 years, the fruits of his efforts were brought
to the attention of the Radio Board of the Danish Post Office,
which controls broadcasting in Denmark, the Radio Board secretly
granted him a large sum to support further work. Some weeks
ago he concluded his experiments and placed before an audience
of experts (led by the chief engineer of broadcasting) - the
The Renode timed its appearance on the market at a psychological
hour when the whole Scandinavian (Denmark, Norway, Sweden, and
even Germany) radio industry is combining in a fight against
the international tube and patent trusts.
In addition to the high prices for tubes (an American 50¢
tube sells in Denmark as a result of trust manipulations, for
about $5.00!), of which about 1/2 million are imported annually,
the national receiver-production in Denmark has been liable
to payment of considerable royalties to holders of certain vital
patents. It is utterly impossible to build a modern tube set
legally unless sanctioned by the Dansk Radio Union (comprising
38 companies manufacturing radio equipment in Denmark), which,
until now, has had complete control of set production. Now,
however, with the advent of the Renode, four of the larger manufacturers
have withdrawn from the Union, and are pinning their faith on
the new tube!
The Norwegians are in much the same fix as the Danes, as
far as tube prices and patent licenses are concerned. In addition,
broadcasting is having a very tough time in Norway right now,
since the mountainous country necessitates a large number of
comparatively powerful broadcasting stations. But the building
and expansion of such a network, to service only 175,000 listeners,
who pay an aggregate license fee of about 3 1/2 million kroner
annually, is very expensive. In an effort to acquire more revenue
an attempt was made to increase the number of listeners by designing
a very inexpensive radio set - a Norwegian edition of the German
"Volksempfänger;" or All-Peoples Receiver. However, real
production has been withheld simply because the broadcasters
are openly afraid that the international tube and patent firms
will hamper the practical development by taking their toll on
tubes and patent licenses.
We find in Sweden that the association of Swedish radio manufacturers
is having a terrific battle with the tube firms, which are alleged
to have attempted to exercise a regular dictatorship over the
So, if the international trusts do not succeed in buying
the Danish Renode people out - and I, for one, am perfectly
satisfied they will not give in - it should be obvious that
the Renode spells war on all other tube firms.
Posted September 13, 2015