US2353677A - Arrangement to disconnect transmitter tubes - Google Patents

Description

July 18, 1944. w. KUMMERER ARRANGEMENT TO DISCONNECT TRANSMITTER TUBES Filed July 8, 1941 INVENTOR BY ATTORNEY Patented July 18, 1944 ARRANGEMENT T DISGONNECT TRANSMITTER TUBES Wilhelm Kummerer, Berlin, Germany; vested in the Alien Property Custodian Application July 8, 1941, Serial No. 401,473 In Germany May '23, 1940 8 Claims.

This invention is concerned with an arrangement adapted to cause disconnection of the plat potential of transmitter tubes upon the occurrence of flashovers or short-circuits.

It happens occasionally that flashovers are produced in high-vacuum tubes while they are in actual operation, for example, as a result of gas release, and this is liable to result in arcing. Unless such an arc is. speedily broken, it will destroy parts of the electrodes with the result that the tube is rendered unserviceable. It is therefore necessary to disconnect the potential as fast as feasible from such a tube immediately after the production of an are or flash-over or internal breakdown.

Now, safety and protection devices have been disclosed in the prior art which are predicated for their operation upon a relay which is traversed and energized by the plate current, the relay responding to the sudden rise of the current as a result of a fiashover in a tube thereby causing disconnection of the plate potential rectifier. In the direct current circuit of the plate supply is included, moreover, a resistance in circuit organizations of thi kind which is designed to limit the short-circuit current. From the instant the flashover of the tube happens until the oil-break switch is opened, there is an appreciable lapse of time inherent in the time mechanical switches take for response; and throughout this entire period the entire short-circuit current flows through the flashover or are and this is likely to eventuate in destruction of the tube.

To avoid this difliculty, it is possible to use gridcontrolled rectifiers upon the grid of which a blocking potential is impressed in case of a shortcircuit, To be sure, in this arrangement, the cutoff of the rectifier is produced inside a few thouandths of a second; however, the flow of current through the flashover or are ceases only when the phase of the rectifier which happens to burn passes through zero. Quite apart from this shortcoming, however, this mode of insuring disconnecticn inheres the further drawback that the energy stored up in the filter is also drained by way of the arc. Where transmitters of extremely large power are concerned, this alone may cause damage to the tube or render it completely unserviceable.

There is known in the prior art another arrangement designed to cause disconnection of the plate potential of large-power transmitters upon the production of fiashover or arcing in which between filter and transmitter tube is arranged an inertialess or non-sluggish disconnecting device operating with Thyratrons for high potential direct current. Tripping of the disconnecting arrangement occurs by way of a transformer included in the plate circuit; the said transformer upon the sudden production of a rise of current ignites an auxiliary discharge device from which a counter-acting potential is impressed upon a grid-controlled rectifier included in the plate circuit to compensate the burning potential thereof, with the result that the discharge ceases.

Now, all of these disconnecting or circuit opening mean responding to increase of current upon flashover do not operate satisfactorily whenever the plate circuit of the transmitter tube contains an inductance, say, the output winding of a modulation transformer. If the plate circuit includes such a modulation transformer, then this highspeed relay or the impulse transformer must be so proportioned that no disconnection will be occasioned when the plate current attains twice the normal direct current value, for it will be noted that upon the direct current L1: is superimposed by the modulation a tonal frequency A. C. Ia the crest value of which, in the presence of per cent modulation, is equal to the direct current. If, then, the transmitter tube experiences a fiashover, so that the drop of potential across it becomes suddenly very small, the sudden rise of the current will nevertheless be very small inasmuch as the internal resistance of the modulator tube transferred to the output end of the modulation transformer is rather high. Then, the plate current through the inductance of the output end of the modulation transformer begins to rise at a delayed rat and the relay or the disconnecting device will respond only after the current ha gone sufficiently far beyond the level 210.: However, in the meanwhile, the flashover in the tube may have already resulted in damage to the tube. This shortcoming of the scheme will become so much more apparent where more rather than only one tube are used. For in that case, the particular tube that has suffered flashover or arcing will immediately take the plate current of all of the other tubes, and it is only when the aggregate current has surpassed the value 2Ia= that the relay and thus the disconnecting switch are able to respond.

Now, in an arrangement designed to cause disconnection of the plate potential for transmitter tubes, in case of flashovers or short-circuits according to the present invention, two potentials are impressed upon a relay, one thereof being proportional to the plate direct current volta e acting at the tube, while the other one is proportional to the plate direct current of the tube, these potentials being chosen of such a value that under normal operating conditions, there will arise no potential difference at the relay. According to a further object of the invention, means are provided which are designed to prevent a discharge of the energy contained in the filter means through and across the tube fiashover point or arc.

The invention will now be described in more detail by reference to the appended drawing in which Fig. 1 shOWs a basic circuit diagram of a push-pull modulated transmitter class B amplifier, and Fig. 2 shows a circuit diagram of another amplifier with a spark-gap.

Referring now in detail to Figure 1, I denotes the grid-controlled multi-phase rectifier which produces the plate potential Ua: of the transmitter power stage and usually also of the AF power stage. In the rectifier circuit are included the filter choke-coil 2 and the smoothing capacity 3. The two power tubes 5 and 6 of the push-pull class B amplifier work upon the modulation transformer 4, the output winding of which is connected in series with the transmitter tube, the output potential Uathereof being superposed upon the plate direct current voltage Ua: so that the transmitter stage comprising elements I, 8, 9, is subjected to plate potential modulation. Instead of a tube I, it would also be feasible to parallel a plurality of tubes. 8 denotes the plate oscillatory circuit, while 9 stands for the plate blocking condenser of the power stage which is chosen only of such a size that the resistance thereof for radio frequency turns out to be sufiiciently low.

To produce the two potentials required for the operation of the relay, a voltage divider II] is connected in parallel relation to the plate blocking condenser 9. The potential taken off at points or terminals a and b of this voltage divider is proportional to the superposed audio frequency potential Ua-. Furthermore, a resistance II is cut in the cathode lead of the transmitter tube or tubes. The drop of potential which arises across the said resistance I I is proportional to the plate direct current Ia: and the plate alternating current Ia-. The size of the said drop of potential, according to the invention, is chosen so high that the potential across terminals a and b is equal to the drop of potential across resistance II. Then, no potential difference will arise across terminals I2 and I3 which are connected with points I) and 0. Between these points is connected according to the invention a high-speed relay which may be provided with suitable contacts. Now, as soon as a flashover occurs in the tube I, the voltage of the transmitter stage, that is, across 9 and I9, collapses immediately and thus also the voltage across points a and b so that instantaneously a voltage arises across points I2, I3 which is equal to the drop of potential across resistance I I. The high speed relay connected between I2 and I3 is about to respond immediately and the rectifiers producing the plate direct current voltage as a consequence are cut off. The arrangement here disclosed offers the advantage, as can be seen from what precedes, that in case of a tube flashover the high-speed relay will be caused to become operative and respond even when the supplied current has not yet suffered any alteration.

In actual operation and service, there is no need to make the high-speed relay too sensitive. On the contrary, means to adjust the sensitiveness may be expedient and to set the relay so that, in

the case of small load fluctuations associated with alterations of the plate current such as may be occasioned, say, by variations of the tuning or the coupling in any of the circuits of the transmitter equipment, there will be no response. In some instances, for instance, in transmitters modulated in one of the earlier stages, it will be preferable to use a polarized relay which will be caused to respond only upon the electrical quantities being changed in a definite sense.

Where transmitters involving very high powers are dealt with, the protection afforded by the relay responding upon a fiashover of a tube will not be adequate if it merely blocks the grids of the multi-phase rectifier in Fig. 1. The capacity 3, as will be seen, is so high where transmitters of extra large power are concerned that even by immediate cut-01f of rectifier I, the energy of condenser 3 becoming discharged through tube I will suffice to occasion destructive actions in the tube. Hence, according to a further object of this invention, additional means are provided designed to preclude discharge of the condenser through a flashover or are in case this has been produced in a tube. In the case of large-power transmitters, therefore, according to the invention, the relay connected between I2 and I3 fulfills this further purpose to initiate instantaneous discharge of the condenser through a resistance upon the occurrence of a tube flashover. Such an example is schematically illustrated in Fig. 2.

In the exemplified embodiment shown in Fig. 2, a horn-type discharge-gap I5 is connected with the two terminals of the condenser 3 by way of a discharge resistance I4, and in the neighborhood of the said horn spark-gap is a needle-point electrode I6 which is united with a high-potential coil (Tesla coil) IT. NOW, as soon as a fiashover happens in the transmitter tube I, the relay connected between I2 and I3 cuts in circuit a radio frequency generator I8 which is designed to set up in the high voltage coil I1 such a high potential that the needle electrode I6 begins to exhibit corona, that the condenser 3 has a chance to dis charge through resistance I4 and the sparks between the electrodes I5.

Instead of causing the relay between points I2 and I3 to start operation of the radio frequency generator for the flashing of the spark-gap, it would also be possible to use directly the potential between I2 and I3 arising upon a fiashover for the purpose to initiate oscillating in the auxiliary transmitter I8. In the absence of a potential difference between I2 and I3, under normal operating conditions such a high negative biasing voltage will then prevail at the grid of the radio frequency generator tube I8, which is furnished from the source of voltage supply I9, that the said auxiliary transmitter i8 will have no chance to start oscillating. A coupling condenser 26 is connected between the high voltage coil II and the anode of transmitting tube Upon the occurrence of a disturbance or trouble in the transmitter tube, a voltage arises between I2 and I3 which is in opposition to the biasing potential so that the negative biasing voltage or transmitter I8 diminishes to a point where it is able to start oscillating, with the consequence that by way of II discharging of condenser 3 is initiated. So far as the said auxiliary transmitter I8 is concerned, a very small power will sufiice since it serves solely to flash the spark-gap. The frequency of the same is chosen so high that oscillating is started as fast as feasible.

The circuit organization for the exemplified embodiment Fig. 2 shows also that the cathode of the auxiliary transmitter I8 is not at ground potential. Hence, the tube is preferably heated by way of a transformer, while the plate potential is preferably produced by means of a dry (oxide) type rectifier. If several tubes ar used in the wave generator, then the plates thereof may be fed with a multi-phase potential rather than direct current potential. All that is necessary is to choose the potential in such a way that there will always prevail a positive potential at least at one tube so that the auxiliary transmitter is able to start oscillating at any time.

In lieu of the spark-gap l5, Fig. 2, could be used also a controlled Thyratron tube or the like, mercury rectifier tube having the property whereby, if the grid electrode is maintained negative beyond a critical value, no anode current will flow even though high values of positive potential be applied to the anode electrode. However, if, while the anode electrode is positively charged, and the negative voltage applied to the grid electrode is reduced beyond a critical point, anode current will commence to flow and. having commenced to flow, will continue to new un-- til the positive polarization or charge is removed from the anode electrode. The are through the tube then can only be started by applying the critical voltage to the grid. After starting the arc the flow or continuance thereof can not be affected by the grid, but it can be stopped 'by removing the anode voltage. The tube therefore operates with an intermittent arc discharge whose average current is controlled by the grid. If further information as to the operation of a tube of this type under the conditions indicated above is required, reference may be made to an article by Hull appearing on page 390 of the Gen-- eral Electric Review for July, 1929 (volume 32 No. 7). Therefore, such a rectifier tube, in case of flashover in the transmitter tube, is ignited. Because of the potential difference between points l2 and i3 and the controlled Thyratron it is necessary to insure insulation between the igniter circuit and points 12 and It. For instance, the output potential of the auxiliary transmitter 18, after rectification, may be employed for starting or striking the rectifier.

Where transmitters designed for a relatively wide band are concerned, that is, transmitters working with low carrier frequency, or transmitters having a very low-damped antenna circuit or output circuit, the transmitter stage i, 8, Fig. l, for high modulation frequencies no longer behaves like a purely ohmic, but rather like a complex resistance. In that case, for high modulation frequencies, a phase displacement angle prevails between the alternating potential Uaat the voltage divider II] and the alternating current Iawhich flows through the resistance H, with the result that an alternating potential rises across points l2 and I3. In other Words, where transmitters of this kind are concerned, conditions must be made so as to prevent relays or protective or safety means connected across points I2 and I3 from responding. In some cases, it may suffice to set the relay to a point where it is less sensitive, in other words, in such a way that it will respond only when a certain threshold value is exceeded. The situation becomes most simple where it is permissible to narrow th bandwidth to a sufficient degree. If steps in that direction are not possible, or not adequate, then a low-pass filter may be cut in between the terminals I2 and I3 and the relay or other safety device designed to suppress the higher modulation frequencies for which the transmitter is no longer ohmic in nature.

Where extra large plate modulated transmitter equipment is involved, it may occasionally become necessary to destroy and suppress also the energy of the modulation transformer 4 by means of the same kind as those provided for the condenser 3. If desired, the discharge device l4, I5, Hi could be used jointly for 3 and 4.

What is claimed is:

l. A transmitter circuit arrangement for disconnecting the plate potential of an electron discharge device upon an abnormal operation thereof, comprising an electron discharge device having a plate, grid and cathode electrodes, a rectifier circuit connected to said electron discharge device for supplying a direct current thereto, a relay circuit for cutting ofi the direct current supplying said electron discharge device, resistance means connected to said rectifier circuit to produce two different potentials required for operating said relay circuit, one of said potentials being proportional to the plate direct current voltage acting on said electron discharge device, the other potential being proportional to the plate direct current of said electron discharge device, and both of said potentials being arranged by said means so that under normal operating conditions the relay circuit is in an inactive state and in an active state only under abnormal operating conditions of said electron discharge device.

2. A transmitter circuit arrangement for disconnecting the plate potential of an electron discharge device upon an abnormal operation thereof, comprising an electron discharge device having a plate, grid and cathode electrodes, a rectifier circuit connected to said electron discharge device for supplying a direct current thereto, a relay circuit for cutting off the direct current supplying said electron discharge device, resistance means connected to said rectifier circuit to produce two different potentials required for operating said relay circuit, a condenser circuit connected across said rectifier circuit, an auxiliary transmitting device including an electron discharge device connected to said relay circuit, a spark-gap connected across said condenser circuit, a needle electrode located intermediate said spark-gap and connected to said auxiliary transmitting device to ignite upon a discharge of said condenser, said relay circuit being operated by having impressed thereon two poteniials from said means, one of said potentials being proportional to the plate direct current volttage acting on said electron discharge device, the other potential being proportional to the plate direct current of said electron discharge device, and both of said potentials being arranged by said means so that under normal operating conditions the relay circuit is in an inactive state and in an active state only under abnormal operating conditions of said first mentioned electron discharge device.

3. A transmitter circuit arrangement as claimed in claim 2 wherein said auxiliary transmitting device is directly controlled by the two different potentials acting on said relay circuit so that the grid of its electron discharge device is biased with a potential such that the auxiliary transmitter is induced to oscillate and thus cause said spark-gap to flash when an abnormal operating condition prevails on said first mentioned electron discharge device.

4. A transmitter circuit arrangement for disconnecting the plate potentials of an electron discharge device upon an abnormal operation thereof, comprising a plurality of electron discharge devices each having a plate, grid and cathode electrodes, a rectifier circuit connected to said electron discharge devices for supplying direct current thereto, a relay circuit for cutting off the direct current supplying said electron discharge devices, resistance means connected to said rectifier circuit to produce two different potentials required for operating said relay circuit, one of said potentials being proportional to the plate direct current voltage acting on said electron discharge devices, the other potential being proportional to the plate direct current of said electron discharge devices, and both of said potentials being arranged by said means so that under normal operating conditions the relay cir" cuit is in an inactive state and in an active state only under abnormal operating conditions of said electron dischargedevices.

5. A transmitter circuit arrangement for disconnecting the plate potential of an electron discharge device upon an abnormal thereof, comprising an electron discharge device having a plate, grid and cathode electrodes, a rectifier circuit connected to said electron discharge device for supplying a direct current thereto, a relay circuit for cutting off the direct current supplying said electron discharge device, resistance means connected to said rectifier circuit to produce two different potentials required for operating said relay circuit, a condenser circuit connected across said rectifier circuit, an auxiliary transmitting device including an electron discharge device connected to said relay circuit, an electron discharge device of the type in which a flow of current is initiated by a critical grid potential and continuance of said flow of current is maintained as long as a positive potential is applied to the anode of said electron discharge devices, said relay circuit being operated by having impressed thereon two potentials from said means, one of said potentials being proportional to the plate direct current voltage acting on said electron discharge device, the other potential being proportional to the plate direct current of said electron discharge device, and both of said potentials being arranged by said means so that under normal operating conditions the relay circuit is in an inactive state and in an active state only under abnormal operating conditions of said first mentioned electron discharge device.

6. A transmitter circuit arrangement as claimed in claim 2 wherein said auxiliary transmitting device comprises a plurality of electron disoperatio-n charge-devices and the rectifier circuit includes a multi-phase potential circuit in which at least one of said electron discharge devices will have a positive plate potential prevailing so that said auxiliary transmitting device is able to start oscillating at any time.

'7. A transmitter circuit arrangement for disconnecting the plate potential of an electron discharge device upon an abnormal operation thereof, comprising an electron discharge device having a plate, grid and cathode electrode, a rectifier circuit connected to said electron dis charge device for supplying a direct current thereto, a relay circuit for cutting off the direct current supplying said electron discharging device, a modulation transformer having one of its windings connected in series between the plate of said electron discharge device and said rectifier circuit, a low-pass filter connected across said relay circuit to suppress high modulating frequencies in said modulation transformer windings, resistance means connected to said rectifier circuit to produce two different potentials, required for operating said relay circuit, one of said potentials being proportional to the plate direct current voltage acting on said electron discharge device, the other potential bein proportional to the plate direct current of said electron discharge device, and both of said potentials being arranged by said means so that under normal operating conditions the relay circuit is in an inactive state and in an active state only under abnormal operating conditions of said electron discharge device.

8. A transmitter circuit arrangement for disconnecting the plate potential of an electron discharge device upon an abnormal operation thereof, comprising an electron discharge device having a plate, grid and cathode electrodes, a rectifier circuit including a plurality of grid controlled rectifiers connected to said electron discharge device for supplying a direct current thereto, a relay circuit for cutting off the direct current supplying said electron discharge device, resistance means connected to said rectifier circuit to produce two different potentials required for operating said relay circuit, one of said potentials being proportional to the plate direct current voltage acting on said electron discharge device, the other potential being proportional to the plate direct current of said electron discharge device, and both of said potentials being arranged by said means so that under normal operating conditions the relay circuit is in an inactive state and in an active state only under abnormal operating conditions of said electron discharge device.

WILHELM KUMMERER.

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