GB2033144A - A high vacuum valve - Google Patents

Abstract

A high vacuum valve incorporating two valve systems - a diode-triode or diode-tetrode as described - includes a common, annular, cylindrical cathode, with lead K as shown; a first anode, with lead Ar, disposed around the cathode, with the interposition of grid electrodes G2 and G1, to form a high power tetrode; and a second anode, with lead Ad, disposed in the space bounded by the cathode, to form a lower power diode. The use of the valve in a pulse-length-modulated switching amplifier is described (Figure 2). <IMAGE>

Description

SPECIFICATION A high vacuum valve The present invention relates to a high vacuum valve.

Receiver valves have been disclosed in which two valve systems are accommodated either above each other or beside each other in a common vacuum container with a common socket. Mostly, a common heater filament is used for heating separate, indirectly heatable cathodes. The dissipation of the loss heat takes place by means of radiation heat through the high vacuum to the vacuum container and from there by means of convection.

In high power valves, especially transmitting valves, a composition of several valve systems in a common high vacuum container has not hitherto been carried out. It also does not appear sensible when the problems are considered, which arise with such high power valves.

It is firstly to be considered that the anode of a high power valve is to be cooled directly because of the high loss loads to be dissipated, for example through a forced air current, through a water current or by way of boiling cooling. The anode is therefore mostly constructed as part of the vacuum container at the same time. For this, it is evident that there is little sense in arranging two valve systems beside each other for high power valves, because no round vacuum container could any longer be used and there would hardly be any constructional space saving.

There is also little sense with high power valves in placing above each other two valve systems in a common vacuum container because the feeds to the electrodes of the upper system would then have to be brought through the lower system to the socket.

Also, such a long mode of construction of a high power valve with two systems can lead to cavity resonances within the systems. With boiling cooling, too, it is endeavoured not to allow the length dimension of a valve to become too great in order that uniform cooling can still be attained.

In a commercially available transmitting triode, a short mode of construction is attained in that a part of the control grid is disposed in the interior of a hollow cylindrical cathode as well as round the outside and both the control grid parts are enveloped by a single anode which is constructed annularly with U-shaped cross-section and is cooled in the centre as well as outside by water.

It has however proved that thermal problems can arise in the inner part of this valve system and influence the duration of its life, while such problems occur to a lesser extent in the outer part of the valve system.

In transmitting techniques, in place of one thoroughbred high power valve, two transmitting valves have been used which are connected in parallel to each other with the same life expectancy. One is thereby not forced in case of a defect of one valve to replace more than this valve.

In other circuit arrangements, in which valves which are not completely similar are connected together, the expenditure for one of the valves is sometimes found to be disturbingly high. For example DE-PS 12 18557 discloses an amplifier which can be used as a modulation amplifier for the anode voltage modulation of a high frequency transmitting valve, a switching valve being connected with a freewheel diode. The oscillation to be amplified is converted before amplification into a pulse-duration modulated pulse, by which the switching valve is controlled. Current flows through an energy store and alternately through the switching valve and the freewheel diode. A low-pass filter is connected behind the switching valve to suppress harmonics of the pulse frequency (switching frequency).

For example, in such a so-called D-amplifier, executed as a modulation amplifier for a large transmitter with a power in the order of for example 100 kilowatts or more, the effort for the freewheel diode is then found to be burdensome when it is executed as a vacuum rectifier as well as when it comprises a chain of semi-conductor valves (DBGM 7 439 808). The previous solutions appear less satisfactory since although the freewheel diode in itself requires relatively little dissipation loading in relation to the switching valve, special precautions for the cooling of the freewheel diode are nevertheless necessaryforthis.

According to the present invention, there is provided a high vacuum valve comprising a vacuum container, a first and a second electrical system disposed within the vacuum container and comprising an annular cathode, the first system comprising a first anode disposed around the cathode and the second system comprising a second anode within the space bounded by the cathode and being adapted for a lower dissipation loading than the first system.

In high power valves, for example transmitting valves, the cathode is mostly in the form of a hollow cylinder and is directly heated. The space surrounded by it can therefore be utilized for a second valve system with a lower dissipation load than the outer (first) system. With this co-axial arrangement, there is the advantage that mountings for the one system do not have to be brought through the other system and that at least a carrying part of one system, for example the anode of the second system, can also be utilized for the other system, for example as part of a mounting of one electrode. thus significant constructional simplifications, a reduction of the space required and, in some circumstances, a reduced heater power requirement result.

Particularly when the inner system is a diode, the composition of both the systems in a common vacuum container entails no problems in respect of life duration, because the additional costs for the diode system in the high vacuum valve are small and the life expextancy of a diode mostly greater than that of the first system, which is preferably constructed as a controllable valve system, for example as a triode or tetrode.

With the use of the high vacuum valve as a switching valve and a freewheel diode in a switching amplifier, the life duration of the common cathode might even be increased compared with the use of separate valve systems, because the common cathode is no longer loaded in pulse shape in the rhythm of the switching frequency, but the space charge cloud surrounding the directly heated cathode is conducted away alternately from one of both the anodes.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a circuit diagram for a known switching amplifier, Figure2 shows a circuit diagram in which a high vacuum valve embodying the present invention is employed, and Figure 3 shows the internal construction of a high vacuum valve embodying the present invention.

Figure 1 is based on Figure 8 of DE-PS 12 18557 and corresponds substantially to the upper part of Figure 1 of German Patent Application P 2715133. A switching valve 4 is fed through a choke 3 and a transmitting valve 6, which is illustrated only as load resistance, through a low pass filter 5 from a unidirectional voltage source 1, which is connected in parallel with a capacitor 2. The modulation voltage needed for the anode modulation of the transmitting valve 6 is put at disposal by the switching valve 4, which is driven by pulses which are pulsemodulated in the rhythm of the modulation oscillation. A driver 7, at the input 8 of which the pulse-duration modulated pulses are illustrated, serves for the driving of the switching valve 4 by way ofthe control grid G1.

The switching valve 4 is constructed as a tetrode with a screen grid G2. The heater currentforthe cathode Kcomesfrom a heatertransformer9, having a secondary winding which is bridged over in terms of high frequency by centre tapping of capacitors 10.

In the conductive state of the switching valve 4, current flows through the choke 3 through the switching valve 4 to the low pass filter. Since a choke 11 is coupled with the choke 3, so that both together act as energy store in the form of a storage choke, the current on blocking the switching valve flows through the choke 11 and a freewheel diode 12. This current is designated by Id, while the current flowing through the switching valve 4 is designated by Ir.

Both currents together complement themselves in the low pass filter 5 into a unidirectional current, however superimposed by the modulation oscillation, by which the input pulse at the input 8 of the driver 7 is pulse-duration modulated. Also residuals of the switching frequency of for example 50 kiloHertz, by which the switching valve 4 is switched, appear at the switching point 13. These residuals are filtered out by the low pass filter 5 so that passing to the transmitting valve 6 is onlythe modulation oscillation of the pulse-duration modulated pulses, which can comprise a mixture of sound oscillations and for the amplification of which the switching valve 4 with the freewheel diode 12, the energy store 3 and 11 and the low-pass filter 5 are provided.

For a transmitter with a power in the order of 100 kilowatts or more, it has hitherto been attempted to build up the driver 7 and the freewheel diode 12 from semi-conductor components, while a vacuum valve was used for the switching valve 4.

By combining the switching valve 4 and the freewheel diode 12 in a single vacuum container substantially reduced production costs for a switching aplifier and a constructionally simplified build-up results.

The high vacuum valve is designated by 14 in the circuit diagram shown in Figure 2, in which the reference symbols for like components are the same as in Figure 1. It contains a cathode K common to the controllable valve system and the diode system. The diode system is additionally formed by the diode anode Ad, while the controllable valve system apart from the cathode K still contains the grids G1 and G2 and the valve anode Ar.

Figure 2 shows that the current leads could be improved since only unidirectional current with superimposed, low-frequency modulation current (Id + Ir) still flows out of the cathode K of the high vacuum valve 14. Accordingly, pulse current (proportional to Ir) is no longer coupled out in Figure 2 as in Figure 1 in direction of the arrow 15 from the primary side of the heater transformer 9, because the secondary winding of the heater transformer 9 according to Figure 2 is flowed through by the current Id + Ir.

The connections 16 and 17 to the anodes Ad and Ar can be twisted together or arranged co-axially since the much larger capacitance of the capacitor 18 is parallel to them.

In Figure 3, the internal construction of an embodiment of a high vacuum valve is illustrated schematically and in perspective in a partially cutopen state.

The connections to the electrodes are provided with the same reference symbols as the electrodes themselves in Figure 2. The second anode of the second system (diode anode Ad) is arranged within the hollow space of the cylindrically hollow cathode K.

Provided for the common cathode K is a single hollow cylinder which is provided for electron emission internally as well as externally once for the second system (diode system) and once for the controllable (pulse-duration modulated switchable) first system (tetrode system). The second system is designed for a substantially lower (for example a quarter) dissipation load than the first (controllable valve) system.

Figure 3 shows that the anode connections AD and Ar extend from the upper side of the high vacuum valve, and the cathode connections from the lower side, from the vacuum container (not shown).

In this manner, no insulation problems arise at the valve socket and the capacitances between the anodes do not disturb since they are parallel to the capacitance of the capacitor 18 in the circuit shown in Figure 2.

By arranging the diode anode Ad within the cathode K, the cathode is optimally utilized for both the systems, the valve system and the diode system, the mechanical construction which is shown in Figure 3. Cooling of the diode anode is in some circumstances not required since the dissipation load of a vacuum rectifier, as which the freewheel diode is constructed within the high vacuum valve 14, is practically determined only by the current and the residual voltage and is therefore relatively small.

The dissipation load occurring on switching in the pulse edges appears at the outer anode Ar of the first system (triode or here tetrode). A heating of the cathode arises through the dissipation load of the internally arranged diode Ad, which is about equal to the heater power. Thereby, a saving of heater power is possible.

A substantial simplification of the circuit construction by omission of a separate vacuum rectifier or a semi-conductorfreewheel diode (12 in Figure 1) and an increase in reliability can be attained since the semi-conductorfreewheel diode in a high power transmitter for example comprises a series connection of over 100 individual semi-conductors.

By reason of the co-axial build-up of both the systems according to Figure 3 with a common cathode, this at the same time acts as a screen between both the systems. The use of the high vacuum valve in a pulse-length modulated switching amplifier with conductive connection of the cathode of the freewheel diode and the cathode of the switching valve is therefore preferable.

Claims (11)

1. A high vacuum valve comprising a vacuum container, a first and a second electrical system disposed within the vacuum container and comprising an annular cathode, the first system comprising a first anode disposed around the cathode and the second system comprising a second anode within the space bounded by the cathode and being adapted for a lower dissipation loading than the first system.

2. A valve as claimed in claim 1, wherein the cathode is operatively associated with each system.

3. A valve as claimed in either claim 1 or claim 2, wherein one of the systems comprises a support member which is operatively associated with the other system.

4. Avalve as claimed in any one of the preceding claims, wherein the first system has a mean life expectancy which is unimpaired by the life expectancy of the second system.

5. A valve as claimed in any one of the preceding claims, comprising first and second anode connections leading from one axial end portion ofthe cathode and a cathode connection leading from the opposite end portion of the cathode to wall means of vacuum container.

6. Avalve as claimed in any one of the preceding claims, wherein the first system comprises a controllable valve system and second system comprises a diode system.

7. A high vacuum valve as claimed in claim 6, when used in a pulse-length-modulated switching amplifier with an energy storage means, wherein the first system froms part of the switching amplifier and the second system forms a freewheel diode.

8. A valve as claimed in claim 7, wherein the switching valve and the freewheel diode are conductively connected to a common cathode.

9. A valve as claimed in either claim 7 or claim 8, comprising anodes which are coupled to each other through a capacitor.

10. A high vacuum valve substantially as hereinbefore described with reference to Figures 3 of the accompanying drawing.

11. A high vacuum valve when used in a pulse length modulated switching amplifier with energy storage means, substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawing.