Electron tube, especially transmitting tube, with a device for eliminating interfering retarding-field effects

Electron tube assemble having coaxial electrodes and grids, including a tube with given electrode trajectories and oscillation period, and interfering retarding-field effect elimination means disposed around the tube for generating a magnetic field having field lines running inside the tube substantially parallel to the electrodes and grids deflecting the trajectories of the electrons moving radially with respect to the anode during operation of the tube and substantially perpendicularly intersecting and elongating the trajectories of the electrons for increasing the oscillation period of the electrons and eliminating interfering retarding-field effects.

The invention relates to an electron tube, especially a transmitting tube, 
with a coaxial construction of the electrodes and their grids. 
Such electron tubes are generally known such as from German Patent DE-PS 
No. 26 25 021. 
It is also known to provide means, in a high vacuum electron tube having 
electrodes disposed along cylindrical surfaces and several incandescent 
cathodes, for the generation of a magnetic field parallel to the 
cylindrical electrode surfaces. These generation means are provided in 
order to have the magnetic field help keep the electron stream away from 
the control electrodes at positive control potential of the control 
electrodes and thus be able to reduce the control power. Such a device is 
shown in U.S. Pat. No. 3,610,996 and Swiss Patent CH-PS No. 483 116 
corresponding thereto. 
In the heretofore customary applications, transmitting tubes were always 
operated at residual plate voltages equal to the screen grid voltage in 
tetrodes and equal to the positive control grid voltage in triodes. 
Operation at lower residual plate voltages was not possible with 
conventional grid technology for reasons of limited screen grid and 
control grid loading. 
Only in special application as a pulse width modulator tube (PDM tube) and 
greater loading of the grids in modern grid technology as a prerequisite, 
is operation at zero residual plate voltage desired in order to obtain the 
better efficiency associated therewith. 
However, with higher modulation and residual plate voltages near zero, 
interfering retarding-field effects will occur in electron tubes. These 
effects are also called Barkhausen-Kurz oscillations, such as is shown in 
the publication Lexikon der Hochfrequenz-, Nachrichten- und Elektrotechnik 
by Rint: (High Frequency, Communications and Electrical Engineering 
Lexicon,) Vol. 1, 1957, pages 527 and 528. 
It is accordingly an object of the invention to provide an electron tube, 
especially transmitting tube, with a device for eliminating interference 
retarding-field effects, which overcomes the hereinafore-mentioned 
disadvantages of the heretofore-known devices of this general type, to do 
so at high modulation with residual plate voltages near zero, and to 
eliminate the interfering retarding-field effects (Barkhausen-Kurz 
oscillations) in order to create, in particular, a PDM tube of high 
efficiency. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, an electron tube, especially transmitting 
tube, assembly having coaxial electrodes and grids, comprising a tube with 
given electron trajectories and oscillation period, and elimination means 
for aforesaid interfering retarding-field effect disposed around the tube 
for generating a magnetic field having field lines running inside the tube 
substantially parallel to the electrodes and grids deflecting the 
trajectories of the electrons moving radially with respect to the anode 
during operation of the tube and substantially perpendicularly 
intersecting and elongating the trajectories of the electrons for 
increasing the oscillation period of the electrons and eliminating 
interfering retarding-field effects. 
According to the invention, the electrons moving radially to the anode are 
deflected by the magnetic field disposed almost perpendicular thereto so 
that their trajectory becomes longer. 
In accordance with another feature of the invention, this is expediently 
accomplished by a relatively small magnetic induction B, wherein the 
elimination means has a magnetic induction of approximately 200 Gauss 
which is equal to 200.times.10.sup.-8 Vsec/cm.sup.2, which increases the 
oscillation period of the electrons so that the interfering 
retarding-field effect of the electrons disappears completely. 
In accordance with a further feature of the invention, the elimination 
means is in the form of a permanent magnet system. 
In accordance with an added feature of the invention, the permanent magnet 
system includes a plurality of ploe piece segments disposed around the 
tube. 
In accordance with an additional feature of the invention, the elimination 
means is in the form of an electromagnet system with current-carrying 
coils. 
In accordance with a concomitant feature of the invention, the elimination 
means has a magnetizing current which is the anode operating current of 
the tube. 
The invention offers the advantage that the electron tube, especially 
transmitting tube, makes operation at zero residual plate voltage 
achievable, and the increased ifficiency associated therewith allows the 
application of the tube as a PDM tube. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in 
electron tube, especially transmitting tube, with a device for eliminating 
interfering retarding-field effects, it is nevertheless not intended to be 
limited to the details shown, since various modifications and structural 
changes may be made therein without departing from the spirit of the 
invention and within the scope and range of equivalents of the claims.

Referring now particularly to FIGS. 1 to 4 of the drawing as a whole, there 
is seen an illustration of a tetrode as the electron tube 1. The 
electrodes, i.e. the cathode 4 and the anode 5, as well as the grids, i.e. 
the screen grid 6 and control grid 7, are coaxial or concentric with each 
other, as seen in FIG. 4. FIGS. 1 to 3 show a heater lead 8 of the cathode 
4 having a terminal 9 which is visible. The screen grid terminal 10 and 
the control grid terminal 11 are also shown. A cylinder of the anode 5 is, 
for example, fastened to an anode flange 12. Between the anode flange 12 
and the screen grid terminal 10, there is disposed an insulating section 
13 formed of a material such as glass or ceramic. Other insulating 
sections 14, 15 are disposed between the screen grid terminal 10 and the 
control grid terminal 11 as well as between the control terminal 11 and 
the cathode lead 9, respectively. 
To eliminate interfering retarding-field effects, a device 2 for generating 
a magnetic field is disposed around the tube 1. The device 2 has field 
lines inside the tube 1, which run essentially parallel to the cathode 4 
and anode 5 as well as to the screen grid 6 and control grid 7. During the 
operation of the tube 1, the electrons travel radially from the cathode 4 
to the anode 5. 
The trajectories of the electrons are intersected essentially 
perpendicularly by the field lines 3. This causes the electrons to be 
deflected into circular orbits which have become longer. The consequence 
thereof is that the oscillation period of the deflected electrons is 
increased so that the interfering retarding-field oscillations are 
eliminated. 
The device 2 shown in FIG. 1 for generating the magnetic field 3 includes a 
coil through which a current I flows. The device 2 shown in FIG. 2 is a 
cylindrical permanent magnet coaxially enclosing the tube 1. A permanent 
magnet system is also used to generate a magnetic field 3 in the 
embodiment example shown in FIGS. 3 and 4. In that embodiment example, the 
permanent magnet system of the device 2 includes several substantially 
kidney or hook-shaped pole piece segments which are disposed around the 
tube 1 and have longitudinal axes which run parallel to the longitudinal 
axis of the electron tube 1.