US3693044A

US3693044A - Firing means for discharge tubes

Info

Publication number: US3693044A
Application number: US101334A
Authority: US
Inventors: Gareld I Gilman; Robert H Wallace
Original assignee: Honeywell Inc
Current assignee: Pentax Corp; Honeywell Inc
Priority date: 1970-12-24
Filing date: 1970-12-24
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19
Also published as: DE2158921A1

Abstract

A triggering transformer having windings surrounding a photographic flash tube fires the latter when the transformer primary winding is energized by the closure of a switch. This switch closure also turns off a transistor which then unblocks a light sensitive integrator including an LASCR which receives the flash tube light by reflection. When the integrator has received a predetermined quantity of light, the LASCR turns on and energizes the primary winding of a second triggering transformer having windings surrounding a quench tube connected in parallel with the flash tube. This fires the quench tube which in turn extinguishes the flash tube.

Description

United States Patent Gilman et a1.

[54] FIRING MEANS FOR DISCHARGE TUBES [72] Inventors: Gareld I. Gilman; Robert H. Wallace, both of Littleton, C010.

[73] Assignee: Honeywell Inc., Minneapolis, Minn. [22] Filed: Dec. 24, 1970 [21] App1.No.: 101,334

[52] US. Cl. ..315/57, 315/151, 315/239, 315/241 R, 315/241 P, 315/274 [51] Int. Cl ..H0lj 17/34, H05b 41/30 [58] field of Search ..315/241 P, 241 S, 57, 239, 315/262, 267, 274-275, 344, 241 R, 151;

[151 3,693,044 [4 1 Sept. 19, 1972 2,352,231. 13/1944 Stratton ..315/344 x 2,624,858 1/1953 Greenlee ..313/201 2,977,524 3/1961 Lingle ..315/241 P ux 2,347,715 5/1944 Spencer ..315/267 x 3,340,426 9/1967 Elliott ..315/241 P ux Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin Nussbaum Attorney-Arthur H. Swanson, Lockwood D. Burton and George E. Bodenstein 4 [57] ABSTRACT A triggering transformer having windings surrounding a photographic flash tube fires the latter when the transfomier primary winding is energized by the do sure of a switch. This switch closure also turns off a transistor which then unblocks a light sensitive integrator including an LASCR which receives the flash tube light by reflection. When the integrator has received a predetermined quantity of light, the LASCR turns on and energizes the primary winding of a second triggering transformer having windings surrounding a quench tube connected in parallel with the flash tube. This fires the quench tube which in-turn extinguishes the flash tube.

12 Claims, 7 Drawing Figures PATENTEnsEP 1 9 I972 v 3 693, 044

SHEET 1 OF 2 INVENTORS. GARELD I GILMAN ROBERT H. WALLACE )kwf.

AGENT.

PATENTEDSEP 1 9 1912 F l G. 7 40 1N TORS.

GA D I.

0 T H. WAL

AGIENT.

BACKGROUND OF THE INVENTION The present invention relates generally to apparatus for firing or triggering discharge tubes, such as the gaseous discharge tubes used as photographic or other light sources or as means for controlling such light sources. Specifically the invention relates to the trigger transformer and trigger electrode portions and connections of such apparatus which effect the firing of such tubes when supplied with triggering voltages which of themselves are incapable of firing the tubes.

It is well known in the illumination art to utilize a discharge tube as a source of illumination, the usual procedure being to fire or flash the tube when it is desired to provide illumination. The known apparatus for effecting the controlled firing of such tubes has usually included means for permanently connecting the usual tow electrodes of such a tube across an energy source of suitably high voltage, such as a charged capacitor. In order to provide control of the firing of the tube, the magnitude of this voltage between the main tube electrodes is made to be sufficiently low so that the tube will not break down and discharge by itself, and the tube is provided with some form of firing or triggering electrode. This electrode is so arranged that, when a voltage of suitably high magnitude is applied between it and one of the main electrodes, the tube fires.

The required magnitude of the last-mentioned voltage is such, however, as to make it undesirable in many instances to apply this voltage directly to the control means which is to control the application of this voltage to the triggering electrode. This is particularly true when the tube is being used in the photographic field to provide flash illumination of objects to be photographed, since said control means is usually then the shutter contacts of a photographic camera. Therefore, it has been the usual practice to include in said known apparatus a step-up, or so-called triggering, transformer which is connected between the controlled source of triggering voltage and the triggering elec trode and one main electrode of the tube. The use of such a transformer makes it possible to utilize a relatively low triggering voltage to produce a voltage on the triggering electrode which is sufficiently high to fire the tube. Under these conditions, the triggering voltage can be sufficiently low as to make it practical to control this voltage directly by the camera shutter contacts, even though such a low voltage would, of itself, be incapable of firing the tube. An example of known apparatus employing such a triggering transformer for firing a photographic flash tube upon the closure of camera shutter contacts is included in the apparatus disclosed in the Hoffer et al., U.S. Pat. No. 3,517,255.

The use of a triggering transformer in apparatus for firing a photographic flash tube has been found to be advantageous also in those known forms of such apparatus wherein the firing of the tube is controlled by a photoelectric device, instead of by camera shutter contacts, to provide so-called slave flash illumination. In such known slave apparatus, the tube is usually fired by means, such as a semiconductor device, which operates more satisfactorily at voltages which are lower than those required to fire such a tube directly.

It is also known to utilize a discharge tube of the foregoing type as a means for controlling another tube which is used to produce illumination. Since such a controlling tube is usually fired by means, such as a semiconductor device, which operates more satisfactorily at voltages which are lower than those required to fire such a tube directly, it has been found to be advantageous in the known apparatus of this type to util- 1 ize the above-described trigger transformer and trigger electrode-equipped tube combination. An example of such apparatus, wherein a first tube is used as a socalled quench tube and is fired to control a second tube operating as a flash tube, is also shown in the aforementioned Hoffer et al., patent.

While the above-described known apparatus arrangements have operated in a generally satisfactory manner, they have also been characterized by certain shortcomings. Specifically, it has been necessary to provide each of the tubes in these known arrangements with the aforementioned triggering electrode, thereby increasing the cost and complexity of such tubes and making their manufacture and handling more difficult. Also, it has been necessary in each instance to provide an electrical connection between the triggering transformer secondary winding and the triggering electrode of the associated tube. These connections, including the wires running from thetransformers to the triggering electrodes, have had to be very carefully insulated because of the magnitude of the voltage involved and the compact nature of such arrangements, thereby increasing the cost and complexity of the latter. Also, the presence of such high voltage connections has made these known arrangements subject to failure due to insulation break-down and high voltage flash-over actions.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved form of the discharge tube firing apparatus of the foregoing type, which form is simpler, less costly, more compact, and more reliable than the known forms of such apparatus as described hereinbefore. A specific object of the invention is to provide such improved apparatus wherein the circuit portions which are at the high voltage necessary to fire the tube are confined within the triggering transformer itself and hence do not require special insulating means. A more specific object of the invention is to provide improved apparatus as just specified wherein no tube triggering electrode or any connection thereto or any high voltage connection to the triggering transformer is required.

In accomplishing the foregoing and other desirable objects, the improved apparatus provided in accordance with, and embodying, the present invention includes a triggering voltage step-up transformer which encircles or surrounds the tube which is to be fired, thereby eliminating the tube triggering electrode and any connection thereto. Specifically, the winding means of this transformer surround the envelope of the tube, and include portions which are arranged in mutually inductive coupling relationship in order to provide the desired voltage step-up. Said winding means also include input connections which are so arranged that, when the relatively low triggering voltage is ap plied thereto, a relatively high voltage, of sufficient magnitude to fire the encircled tube, is produced across at least one of the portions of the .winding means, such as a secondary winding portion, and effects such firing. The construction just described therefore permits the tube to be fired without requiring any triggering electrode or any high voltage connectionsor structure external of the transformer.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention may be had from the following detailed description when read in connection with the accompanying drawing, wherein FIG. 1 is a circuit diagram of controlled flash apparatus utilizing the novel tube firing structure according to the present invention for both a flash tube and a quench tube thereof;

FIGS. 2 and 3 are diagrams illustrating a preferred manner in which the windings of the triggering transformers of the FIG. 1 apparatus may be constructed and arranged; and

FIGS. 4 through 7 are illustrations of several ways in which the triggering transformers and the tubes of the FIG. 1 apparatus may be mutually arranged.

DESCRIPTION OF THE PREFERRED EMBODIMENT The controlled flash apparatus illustrated in FIG. 1 is one which, on command, effects the firing of a flash tube to produce light to illuminate an object to be photographed by an associated camera, not shown. The apparatus then automatically effects the firing of a quench tube, which firing terminates the production of light by the flash tube, as soon as a predetermined quantity of light has been received by a light sensitive portion of the apparatus. In this way, the apparatus automatically controls the duration of each flash of light produced by the flash tube as required to cause a predetermined quantity of light to reach the film of said camera from the object being photographed, said quantity being that required for the proper exposure of the film.

To this end, the FIG. 1 apparatus includes the usual flash storage capacitor 1 which is connected between the usual supply voltage conductors 2 and 3, and includes a first discharge tube 4 which is utilized as a flash tube and is provided with an envelope 5 and

electrodes

6 and 7. The latter are connected, respectively, to the conductors 2 and 3. The apparatus also includes a second discharge tube 8 which is utilized as a quench tube and is provided with an envelope 9 and electrodes 10 and 11. The latter are connected, respectively, to the conductors 2 and 3.

The means in the FIG. 1 apparatus for firing the flash tube 4 on command include a resistor 12 and a normally open firing switch 13 which are connected in series between the conductors 2 and 3 and have a common junction 14 to which is connected one terminal of a triggering capacitor 15. The switch 13 is representative of the usual camera shutter contacts and/or the The means in the FIG. 1 apparatus for automatically firing the quench tube 8 at a time, subsequent to the firusual open flash or test switch of such apparatus. The

ing of the flash tube 4, at which the apparatus has received a predetermined quantity of light include a light activated silicon controlled rectifier (LASCR) 17 which is arranged to be exposed to light coming from the object being photographed. The LASCR 17 has an anode 18, a cathode 19, and a gate 20. Two resistors, 21 and 22, are connected in series between the conductors 2 and 3, and have a common junction 23. The anode 18 is connected to the junction 23, and the cathode 19 is connected to the conductor 3, whereby the anode-cathode path of the LASCR 17 is connected across the resistor 22. An integrating capacitor 24 is connected between the gate 20 and the conductor 3, whereby the capacitor 24 is connected between the gate 20 and the cathode 19. One terminal of a triggering capacitor 25 is connected to the junction 23.

An NPN transistor 26, having the usual collector, emitter, and base, forms a resetting and gating switch for the capacitor 24. To this end, the collector of the transistor 26 is connected to the upper terminal of the capacitor 24, while the transistor emitter is connected to the conductor 3. This places the collector-emitter path of the transistor 26 across the capacitor 24. The transistor 26 base is connected through a resistor 27 to the junction 14, whereby the base-emitter path of the transistor 26 is connected in series with the

resistors

12 and 27 between the conductors 2 and 3, and is connected in series with the resistor 27 across the switch 13. The tube 8 firing means also includes a triggering transformer 28 which, like the transformer 16, is arranged and connected in accordance with the present invention, as will be described below.

It can be seen from the foregoing description that the FIG. 1 apparatus, except for the form, arrangement, and connections of the triggering

transformers

16 and 28, is the same as the apparatus illustrated and described in the aforementioned I-Ioffer etal patent.

In accordance with the present invention, each of the triggering transformers l6 and 28 is a coreless voltage step-up transformer having winding means consisting of a primary winding and a secondary winding which are inductivelycoupled to each other and which surround or encircle the envelope of the associated one of the tubes 4 and 8. Specifically, according to the preferred construction for the

transformers

16 and 28 illustrated herein, the transformer 16 has a primary winding 29 consisting of a plurality of turns of wire connected between

end terminals

30 and 31, and has a secondary winding 32 consisting of a plurality of turns of wire connected between

end terminals

33 and 34. As best seen form FIGS. 2 and 3, which illustrate a preferred way in which the transformer 16 and its windings may be constructed and arranged, the secondary winding 32 surrounds the tube envelope 5 immediately adjacent thereto, and the primary winding 29 is wound on top of, and surrounds, the secondary winding 32. As seen from FIG. 3, the illustrated transformer is of disk form, and the turns of wire of each of the

windings

29 and 32 are desirably arranged in coaxial layers, with the secondary terminal 34 being-connected to the end of the secondary turns which are at the greatest radial distance from the envelope 5, and with the secondary terminal 33 being at the end of the secondary turns which are closest to the envelope 5. Also, the primary winding terminal 30 is connected to the end of the primary turns which are at the greatest radial distance from the envelope 5, while the primary terminal 31 is connected to the end of the primary turns which are closest to the envelope 5. As indicated, the secondary winding 32 has a greater number of turns than does the primary winding 29 in order to provide the desired voltage step-up action.

Thetransformer 16 is provided with an input connection 35 which connects the primary terminal 30 to the remaining terminal of the capacitor 15, and is provided with an input connection 36 which connects the primary terminal 31 to the conductor 3 and hence to the lower terminal of the switch 13. The secondary terminal 34 is connected bya conductor 37 to the conductor 3 and hence to the electrode 7 of the tube 4. The secondary terminal 33, however, is connected only to the inner end of the turns of the secondary winding 32 and, in fact, is actually merely the inner end of that winding.

The conductors 2 and 3 are provided with

respective terminals

38 and 39 for connecting these conductors, and hence the capacitor 1, to the usual capacitor charging means, not shown. As noted in said Hofier et a] patent with respect to the flash storage capacitor therein, the capacitor 1 is normally maintained in a charged state by the aforementioned capacitor charging means, whereby a relatively high voltage is normally maintained between the conductors 2 and 3 and hence between the

electrodes

6 and 7 of the tube 4. This voltage also appears between the electrodes 10 and 11 of the tube 8. However, the magnitude of this voltage is made to be insufficient to cause the tubes 4 and 8 to break down anddischarge by themselves.

By virtue of the elements and their connections which have been described above, the closure of the switch 13 fires the tube 4. Specifically, the capacitor 15 is normally maintained charged through a path which can be traced from the conductor 2 and through the resistor 12, the capacitor 15, the input connection 35, the winding 29, and the input connection 36 to the conductor 3. Accordingly, the closure of the switch 13 connects the charged capacitor 15 between the input connections and 36 and hence across the winding 29. This applies across the winding 29 the triggering voltage which is across the capacitor 15, which voltage, of itself, is not of sufficient magnitude to fire the tube 4. The appearance of this voltage across the winding 29, however, causes a much higher voltage to be produced across the secondary winding 32, which voltage fires the tube 4. It should be noted that this occurs without the need for any triggering electrode on the tube 4, or for any high voltage connection to the transformer 16. By way of illustration and example, and not by way of limitation, it is noted that the triggering voltage applied to the primary winding 29 may well have a magnitude of the order of 350 volts, while the magnitude of the voltage which is needed to fire the tube, and which is produced by the secondary winding 32, may well be of the order of 2,000 volts.

The tube 4 then conducts and emits light until the charge on the capacitor 1, and hence the voltage between the conductors 2 and 3, drop sufficiently to cause the tube 4 to become extinguished. This action is brought about either by the automatic firing of the quench tube 8, or by the continued conduction-of the tube 4, depending upon the quantity of light received by the apparatus. After the tube 4 becomes extinguished, the

capacitors

1 and 15 recharge to be ready for the next firing of the tube 4. All of this operation is the same as that described in said l-loffer et al patent in regard to the apparatus thereof.

The triggering transformer 28 for the quench tube 8 may well be, and will be assumed herein to be, identical to the transformer 16 as described above. Thus, as shown in FIG. 1, the transformer 28 includes a primary winding 40 having a plurality of turns of wire connected between end terminals 41 and 42, and includes a secondary winding 43 having a greater number of turns of wire connected between

end terminals

44 and 45. As in the case of the transformer 16, the secondary winding 43 surrounds the tube envelope 9 immediately adjacent thereto, while the primary winding 40 surrounds the winding 43. The terminal 45 is the secondary winding'terminal which is connected to the end of the secondary turns which are at the greatest radial distance from the envelope 9, while the terminal 44 is that which is at the end of the secondary turns which are closest to the envelope 9. Also, the primary winding terminal 41 is connected to the end of the primary turns which are at the greatest radial distance from the envelope 9, while the terminal 42 is connected to the end of the primary turns which are closest to the envelope 9.

The transformer 28 is provided with an input connection 46 which connects the primary terminal 41 to the remaining terminal of the capacitor 25, and is provided with an input connection 47' which connects the primary terminal 42 to the conductor 3 and hence to the cathode 19 of the LASCR 17. The secondary terminal'45 is connected by a conductor 48 to the conductor 3and hence to the electrode 11 of the tube 8. The secondary terminal 44, however, is merely the unconnected end of the winding 43.

The operation of the apparatus :in automatically actuating the transformer 28 to cause it to fire the quench tube 8 will now be described. In the manner explained in said Hoffer et al patent, the closure of the switch 13 to fire the flash tube4 simultaneously turns off the transistor 26 and prepares the quench portion of the apparatus for operation. When the transistor 26 turns off, the integrating capacitor 24 starts charging in accordance with the quantity of light received by the LASCR 17. When this quantity reaches a predetermined value, the LASCR 17 turns on and switches to a conductive state. This causes the anode-cathode path of the LASCR 17 to effectively short-circuit the resistor 22 and hence to connect the charged capacitor 25 between the input connections 46 and 47 of the transformer 28 and across the primary winding 40 thereof. The charge which is on the capacitor 25 at this time results from the connection of the capacitor 25 and the primary winding 40 in series with the resistor 21 between the conductors 2 and 3.

When the LASCR 17 turns on, therefore, the triggering voltage across the capacitor 25 is applied across the primary winding 40. This causes a suitably high voltage to be produced across the secondary winding 43, which voltage fires the tube 8,.As in the case of the firing of the tube 4, the tube 8 is fired in accordance with the present invention without any need for a triggering electrode on the tube 8, or for any high voltage connections.

The tube 8 then continues to conduct until the voltage between the conductors 2 and 3 has dropped sufficiently to cause the tubes 4 and 8 to become extinguished. When this occurs, the capacitors 1, l5, and 25 recharge to be ready for the next firing of the tubes 4 and 8.

The transformers l6 and 28 may be arranged in a variety of different ways with respect to their associated tubes. It has been found to be desirable, however, to locate the transformer in each instance so that at least the secondary winding thereof is adjacent, or in the vicinity of, at least that one of the tube electrodes to which the secondary outer end terminal (34 or 45) is connected. An example of a preferred arrangement for the transformer 16 and the tube 4 following this practice is shown in FIG. 4. In the FIG. 4 arrangement, the transformer 16 encircles the tube envelope adjacent the tube electrode 7. This arrangement also desirably minimizes any tendency of the transformer to block the light from the tube 4, while permitting the mounted tube to support the transformer in a compact combinanon.

When the tube is of the form in which the two electrodes are relatively close together within the tube envelope, as is usually the case for tubes which are designed for use as quench tubes, the triggering transformer may well be arranged so that it is adjacent both of the tube electrodes. FIG. 5 shows an example of such an arrangement, wherein the transformer 28 surrounds and is carried by the envelope 9 of the tube 8 at approximately themidpoint of the envelope, and hence is adjacent both of the electrodes 10 and 11.

Another example of a desirable arrangement for use with tubes of the last-described type is shown in FIG. 6. The tube of this arrangement is a quench tube 8 of the known type in which both of the electrodes 10 and 11 protrude from the same end of the envelope 9. This type of tube is well adapted for mounting on a circuit board, and is shown mounted on such a board 49. The transformer 28 again surrounds the envelope 9 of the tube 8 adjacent both of the tube electrodes 10 and 11. As shown, the electrode leads, as well as the ends of the transformer windings, desirably pass through suitable holes in the board 49 and are connected to appropriate conductors on the lower face of the board in the usual manner. Such an arrangement facilitates both the locating and mounting and the connecting of the compact tube and transformer combination.

Still another example of a desirable arrangement for use with tubes of the last-described type is shown in FIG. 7. In this arrangement, the tube 8 is mounted parallel to the board 49. Again, the tube electrode leads and the transformer winding ends pass through the board and locate, support, and connect the tube and transformer combination.

In summary, it is seen that the described apparatus according to the present invention fulfills the objects set forth hereinbefore by including discharge tube triggering means which neither requires nor includes any tube triggering electrode or connections thereto, or any high voltage leads or connections, but which includes a paratus including it, while at the same time increasing the reliability of that apparatus.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In discharge tube apparatus, the improvement comprising a discharge tube having an envelope containing a pair of electrodes,

means arranged for connecting said electrodes across a source of tube energizing voltage capable of producing a discharge between said electrodes once said tube has been fired,

winding means surrounding said envelope and having first and second portions arranged on said envelope in mutually inductive coupling relationship to form a voltage step-up tube triggering transformer, one of said portions having a free end connected solely to said one of said portions, and

first and second winding input connections so connected to said winding means that the application of a triggering voltage of a given magnitude between said input connections energizes the other of said portions to produce across at least said one of said portions a voltage of a magnitude which is substantially greater than the first-mentioned magnitude, and which fires said tube.

2. Apparatus as specified in claim 1, wherein at least said one of said portions of said winding means surrounds said envelope adjacent at least one of said elec trodes.

3. Apparatus as specified in claim 1, wherein said electrodes are adjacent each other within said envelope, and wherein at least said one of said portions of said winding means surrounds said envelope adjacent said electrodes.

4. Apparatus as specified in claim 1, wherein, said portions of said winding means comprise a primary winding and a secondary winding, wherein each of said windings has first and second end terminals, wherein said input connections are connected, respectively, to said terminals of said primary winding, wherein said one of said portions comprises said secondary winding, and wherein said free end is one of said terminals of said secondary winding.

5. Apparatus as specified in claim 4, wherein the other of said terminals of said secondary winding is connected to one of said electrodes.

6. Apparatus as specified in claim 4, wherein one of said windings surrounds the other of said windings.

7. Apparatus as specified in claim 4, wherein said secondary winding surrounds said envelope immediately adjacent thereto, and wherein said primary winding surrounds said secondary winding.

8. Apparatus as specified in claim 7, wherein each of said windings includes a plurality of turns of wire arranged in coaxial layers and connected between said terminals of that winding, and wherein the other of said terminals of said secondary winding is connected to the end of said turns of wire of said secondary winding which are at the greatest radial distance from said envelope and is connected to one of said electrodes.

9. Apparatus as specified in claim 8, wherein the one of said terminals of said primary winding which is connected to the end of said turns of wire of said primary winding which are at the shortest radial distance from said envelope is connected to said other of said terminals of said secondary winding, and wherein said one of said terminals of said secondary winding is connected only to said turns of wire of said secondary winding.

10. Apparatus as specified in claim 1, wherein said tube is a photographic discharge tube, wherein said firing of said tube controls the production of light for illuminating an object to be photographed, and wherein there are included means for applying said triggering voltage to said input connections when said tube is to be fired.

11. Apparatus as specified in claim 10, wherein said tube is a flash tube, and wherein the last-mentioned means include a triggering capacitor and means connected to said capacitor and to said input connections, and including terminals arranged for connection to the shutter contacts of a photographic camera, for normally maintaining said capacitor in a charged state and for alternatively connecting said capacitor directly between said input connections upon the establishment of an electrically conductive path between said terminals, as by the closure of said shutter contacts.

12. Apparatus as specified in claim 10, wherein said tube is a quench tube which is connected in quenching relationship to a flash tube, and wherein the last-mentioned means include a triggering capacitor and means connected to said capacitor and to said input connections, and including a normally non-conductive light responsive switching means arranged to receive light produced by said flash tube and to switch to a conductive state upon receiving a predetermined quantity of light, for normally maintaining said capacitor in a charged state and for alternatively connecting said capacitor directly between said input connections upon the switching of said switching means to a conductive state.

Claims

1. In discharge tube apparatus, the improvement comprising a discharge tube having an envelope containing a pair of electrodes, means arranged for connecting said electrodes across a source of tube energizing voltage capable of producing a discharge between said electrodes once said tube has been fired, winding means surrounding said envelope and having first and second portions arranged on said envelope in mutually inductive coupling relationship to form a voltage step-up tube triggering transformer, one of said portions having a free end connected solely to said one of said portions, and first and second winding input connections so connected to said winding means that the application of a triggering voltage of a given magnitude between said input connections energizes the other of said portions to produce across at least said one of said portions a voltage of a magnitude which is substantially greater than the first-mentioned magnitude, and which fires said tube.

2. Apparatus as specified in claim 1, wherein at least said one of said portions of said winding means surrounds said envelope adjacent at least one of said electrodes.