January 1937 Radio-Craft
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Assuming the 10 enumerated advantages of a gridless vacuum tube
may be added to the 17 enumerated disadvantages of a gridded
vacuum tube, there are 27 reasons, per author Henri Dalpayrat
why one should consider abandoning the 'old style' tubes for
his revolutionary concept.
Part 1 of this 2-part series discussed the unavoidably
negative features of a gridded vacuum tube. Part 2, presently,
extolls the wonders of a gridless tube. Chief among the features
is the use of 'compressor bar' elements that are situated parallel
to the electron flow rather than in series with it. Another
major difference is the cathode element running vertically up
the center of the tube and the cathode wraps around it. If I
had to draw a comparison of gridless versus gridded vacuum tubes
with semiconductor devices, the former more closely relates
to a field effect transistor (FET) and the latter to a bipolar
junction transistor (BJT). I say that because the compressor
bars' action on the electron flow is to change the concentration
(density), effectively having the ability to cut off the current.
Although not related functionally to the BJT, the gridless tube
uses 'collectors' to help control the transconductance.
Gridless vs. Grid Vacuum Tubes
Henri F. Dalpayrat
Ever since the grid element was first incorporated in a vacuum
tube it has been a dogma that all subsequent tubes be similarly
constructed. The author points the way to a new era, in electron
tube designs, in which the previously-discussed disadvantages
of a grid are eliminated by means of a "compressor."
Fig. A - Phantom view of basic gridless tube;
note the "compressors."
By the simple expedient of arranging "compressor" elements
to control by electronic means the electron emission from cathode
to anode, a radically new design in electron tubes is effected.
Coincidentally, many new and important functions are made available;
one of the most outstanding of these is automatic noise suppression;
in this design, both the above- and below-signal-level interference
voltages are counteracted.
the preceding issue of Radio-Craft, an enumeration of several
disadvantages inherent in all grid tubes, were discussed, to
point the way to much-needed improvements in electronic amplifying
The new electronic principle described in the present article,
and discussed in connection with gridless tubes, indicates the
possibility of designing greatly-improved radio vacuum tubes
without adhering to the conventional arrangement of electrodes.
"Grid" Tubes Fundamentally Unsound
Contrary to popular belief, the standard "grid" tubes now
available in the industry, although highly perfected, still
have many objectionable features which cannot be corrected as
long as grids are used, and which cannot be overcome by electrical
The source of most of the difficulties now found in thermionic
amplifiers is in the tubes themselves, and it seems more logical
to produce new and better tubes, rather than to improve an old
and inefficient electronic technique; even though it is now
generally conceded that much is to be gained by attempts to
The average radio engineer, accustomed to think in terms
of "grids," is inclined to take grids for granted, or as almost
indispensable; though a little thought on this subject, along
new theoretical principles, will disclose innumerable and important
advantages derived by the total elimination of all grids!
The great number of new electrical circuits possible with
the new type of "gridless" tubes (here illustrated in theory
and practice) open up new fields for experimentation and invention,
independent of the patent restrictions or technical limitations
usually allied with well-known, well-developed standard tubes.
The Design of Gridless Tubes
One important feature of this invention is the complete elimination
of the grids and their disadvantages.
Another object of the principle disclosed in these illustrations
and data that follow, and the novel combinations of new electrodes
in the devices, is to provide new types of vacuum-tube designs
for a wider range of applications and, generally, greater usefulness
than the now well-known vacuum tubes using a number of solenoid
wire grids, or their perforated equivalent, concentrically positioned
around a heated cathode emitting electrons.
Referring to the drawings, Fig. A shows a new type of amplifying
vacuum tube, or thermionic relay, with an evacuated envelope
made of glass or metal (shown in this figure as glass) on a
base having contact prongs connected within the tube to separate
or similar electrodes. The centrally-located cathode sleeve
is coated externally with rare-earth oxides and heated internally
by a filament. Two plates in close proximity to the cathode
are shown as "collectors," and two wires (rods or hollow metal
cylinders) placed in spaced parallel relations with the cathode
and "collectors" are the "compressor bars," within the anodes
or plates, as shown sectionally in Fig. 1.
The anodes may be separate plates, either electrically connected
or insulated from each other, or formed of a single tubular
plate having its facing surface plates stamped out, to decrease
capacity coupling between the anode and. collectors.
Figure 1 (A, B and C) shows the arrangement of the tube electrodes
mentioned, as seen endwise. The filament-heated, coated cathode
is emitting electrons which are repelled by negatively-charged
electrodes or compressor bars; thus forming 2 electron beams
which are each attracted and collected by the positively-charged
collectors; these have their positive potential regulated to
be much lower than that of the anode plates. The voltage on
the "collectors" is made small enough to allow the compression
of the stream of electrons by the "compressors"; but also high
enough to establish a constant electronic emission to the "collectors"
or absorption electrodes.
Figure 1A shows how a high negative charge, applied on the
compressors, directs all electrons towards the central portion
of the surfaces of the collectors. The combined positive charge
of the collectors and negative charge of the compressors completely
prevents any electrons from reaching the anodes. Note the width
of the electron beams, spreading over the surfaces of the collectors;
in Fig. 1A; while Fig. 1B shows how these electron beams spread
in cross-sectional areas, and impinge upon a larger portion
of the collector surfaces when the negative charge of the "compressors"
Figure 1C shows how a further decrease in negative potential
of the compressors, or even the application of a positive charge
on them, reduces the compression of the beams of cathode electrons,
and allows them to spread over and beyond
Fig. 1 - Approximate representation of gridless
the surfaces of the collectors; thus allowing electrons to
reach the anode plates in the form of 4 electron beams. These
beams vary in electronic density according to the voltage variations
applied on the compressors, which control the direction of the
cathode electrons towards the collector plates, and vary the
number of electrons either absorbed by these collectors or passing
between the collectors and compressors to be received by the
Figure 2 shows how an individual A.V.C., per stage, can be
obtained with the electron- beam compressor tube described above.
In this I.F. (the same principle is applicable at R.F. or A.F.)
amplifier, the signals are applied on the compressors, varying
the electrons passing through to the anode. The D.C. potential
applied on the collectors is obtained through a potentiometer
R and a signal-load ohmic impedance high-resistance) R1. When
the signal voltage variations, or excessive noise impulses,
rise above the A.V.C. signal level, the positive potential of
the collectors is increased through capacity C. The positive
voltage, increasing in these collectors, absorbs a greater number
of electrons from the cathode; thus diverting electrons from
the cathode to the anode streams, and decreasing automatically
the amplification of the tube for only the excessive amplitudes,
as adjusted by the positive absorption potential obtained through
The addition of regeneration to this circuit through a tickler
coil T, connected in the anode circuit at point (X) can be advantageously
utilized for greater sensitivity, improved selectivity, or larger
power output, or accentuation of certain modulation frequencies;
while the voltage-controlling functions, previously described,
enable this circuit to provide stable and constant automatic
regeneration, a feature unusually useful in short-wave reception.
The foregoing described only a few possible applications,
such as individual (per stage) automatic volume control, automatic
regeneration control, and a combination diode and power output
amplifier tube. Other circuits, such as automatic volume control
and noise suppression controls, incorporated in each stage of
a receiver, in order to produce a practical "noiseless" or "static
proof" receiver, will be described, exclusively and for the
first time, in a future issue of Radio-Craft.
Referring again to the advantages of "gridless" tubes, and
more particularly to the type invented by the writer and described
in this article, a number of advantages will be given below.
Fig. 2 - Experimental circuit in analysis
of gridless tube operation.
Advantages of Gridless Tubes
It is one purpose of this invention to eliminate solenoid
wire grids, and the method of passing electrons through spaces
between wires, or slots, or small perforations in any controlling
electrodes. Another purpose is to simplify the mechanical construction
and assembly of parts in tubes, while providing stronger, more
rigid structures, and insuring the manufacturing production
of tubes having uniform characteristics.
Still another purpose is to greatly decrease interelectrode
capacities, and to render practical these tubes for the faithful
amplification of audible frequencies, or the amplification of
very short waves, or the generation of constant oscillations,
Fig. B - Actual gridless tube in an experimental
The "gridless" design also provides a new vacuum tube, having
inherent self-limiting amplification properties, and/or self-selecting
amplitude-selection properties, or automatic current or voltage
stabilizing properties, in addition to their normally intended
functions such as detection, rectification, and/or amplification.
There are many other important advantages to be obtained
by applying the "gridless" principle of construction to tubes
of all types. Some of these features are listed, numerically,
(1) Combine, in a simple manner, several functions in one
electronic device, without one function interfering with another.
(2) Permit the manufacture of simple, inexpensive, small
tubes, practical for short-wave operation, and capable of delivering
(as working models have proven) stable, constant, undistorted
and highly amplified current.
(3) Provide new tube designs, especially applicable to power
output-tube operation and capable of delivering relatively high
undistorted power output, with a minimum of positive voltage
applied on the main output anode.
(4) Reduce or eliminate internal vacuum-tube noises, which
are due to electronic bombardments upon electrodes, or to unwanted
electronic reflections or uncontrollable electronic emissions.
(5) The reduction, or the elimination, of currents in certain
electrodes, in order to minimize a type of output current distortions
caused by these electrode currents.
(6) Inherent ability to limit either their own output current
automatically, within any fixed range of variations, or unwanted
signal or noise amplitudes, either below or above a given intensity
level, as determined by adjustable electrical circuit constants-thus
producing an "anti-noise" tube!
(7) Possibility of modulating several electron beams similarly
and simultaneously, or else differently and independently, as
desired to utilize their various outputs for a common purpose
or for individual and different purposes.
(8) Production of (relatively) very short electron beams
of the full and complete cathode electronic emission, without
resorting to the use of so-called "electron gun" or other electrical
means well-known to the art (which. however, are unable to cause
the utilization of the full cathode emission).
(9) Possibility to cause purposely the liberation of secondary
electrons, by coating certain electrodes with appropriate rare
earth oxides; and to utilize the secondary emission produced
by primary electron impacts thereon to obtain a higher voltage
and/or current amplification.
(10) Another new and advantageous feature (available in one
design) is a novel type of controlling electrode, shaped and
positioned in such a manner as to divide an electronic emission,
radiating uniformly around a cathode, into a number of electron
beams; while exerting electrostatic pressure upon all these
beams simultaneously or independently.
There are many more features and advantages to be found in
the radically-new "gridless" priciple of operation, and tubes
that, by means of "compressor" electrodes, utilize this principle
of operation; but space does not permit further elucidation
at the moment. However, the writer will be glad to answer any
inquiries, concerning the gridless tube, if these inquiries
(addressed in care of Radio-Craft) are accompanied by a stamped
and return-addressed envelope.
Posted December 3, 2015p>