Patent GB-198359-A (GB)
Title: Improvements relating to vacuum tube amplifier systems and the like
IPC: H01J19/02
Filed: 1923-05-23
Abstract: 198,359. Western Electric Co., Ltd., (Assignees of Oswald, A. A.). May 23, 1922, [Convention date]. Thermionic oscillation generators, and modulating systems; measuring and testing apparatus.- Relates to high-power amplifying systems for wireless transmission wherein as shown in Fig. 1, the output from a first or low-power stage A is fed to the input circuit cf a bank B of highpower amplifying tubes which in turn supply the aerial circuit C. The filament current is supplied from transformers 15, the plate tension from a common high-voltage generator 9, whilst a second generator 12 furnishes a polarizing potential to the grids, commutator fluctuations being eliminated, by the use of filters F. By suitably back-coupling the input and output circuits of either or both the stages A and B the system may be used as an oscillation generator. The invention is mainly directed towards the provision of suitable automatic protective or safety devices designed to cut off the power supply on the occurrence of any one or more of the following conditions : (a) failure of the grid polarizing supply; (b) reduction below the desired minimum rate of flow of the cooling fluid; (c) over-heating of the cooling-fluid; (d) excessive space-current in any particular amplifying tube. In addition to such provision of automatic control a number of manually operated cut-off switches are distributed at strategic points about the system. Figs. 2 and 3 show the details of the protective devices, Fig. 3 being a continuation to the right of Fig. 2. Grid control. A control circuit extends from the negative terminal of the grid-polarizing generator 12 through resistances 37, 38, contacts 39 - - 42, conductor 43 and coil 44 to ground. Should the circuit be broken the coil 44 releases an armature 35 from a contact 36, which in turn breaks the flow of current through a winding 34 and thereby opens the main switch 17 and so cuts off the high-voltage supply from the generator 9. It is therefore impossible to energize the system unless a proper negative grid voltage is being supplied from the source 12. Flow of cooling fluid. Cooling fluid is circulated around the amplifier tubes through the piping system 21 - - 23 and 59 as shown by the arrows and out through a pressure-controlled alarm system 24 connected with a contact device 25 inserted in the main control circuit. Should the flow stop or slacken, the fluid pressure at the constricted by-pass 27 lowers the level of a mercury layer in a chamber 29, causing a float. 31 to drop and rotate a switch 25. This breaks the main control circuit between the points 42 and so opens the main switch 17. A second contact 72 energized from a transformer 68 shunted across the circuit of the filament supply actuates an alarm bell 70 if the filaments are lit up before the cooling-fluid is in full flow. Overheating of cooling-fluid. If the temperature rises too high, the secondary of the transformer 68 is grounded through the corresponding thermometer 32 and 33, thereby ringing an associated alarm bell 70. Simultaneously the main control circuit from the generator 12 is grounded through a relay 74 and conductor 47 so as to open the main switch 17. Excessive space current. The existence of a dangerously high plate current, in the case of any one of the amplifiers B, Figs. 1 and 3, actuates a relay 7 which releases a detent 52, Fig. 3, and causes a spring-pressed rod 53 to swing against an arm 54 on a spindle 55 and so break a contact 40 in the main circuit controlling the main switch 17. In the case of the amplifiers A, a marginal relay 79, Fig. 2, opens a contact 41 which again breaks the main control circuit. In order to facilitate a quick breaking action of the armature 35 in cases where the main control circuit is merely grounded and not broken a branch circuit is taken from the resistance 38 through a relay 48, resistance 49 and coil 50 to earth through the coil 44. So long as the main control circuit is closed at all points, the branch circuit is practically short circuited, but when the former circuit is actually broken current is diverted through the branch and by energizing the coil 50 accelerates the breaking movement of the armature 35, and therefore the opening of the main switch 17. Master switches 45, 46 are placed at strategic points to earth the main control circuit and open the switch 17 as occasion arises. A restoring switch 51 shortcircuits the resistance 38 on restoring contact be tween the armature 35 and contact 36. Electrically driven clocks PC, FC, Fig. 2, measure the total time during which the filament and plate circuits are energized. A shunt path containing a large condenser 91 which passes the speechfrequency components enables an ammeter 90 to indicate the percentage modulation of the outgoing wave. Short lengths 60 of rubber hose are inserted in the piping system 59 in order to be taken from each tube on a single ammeter A by means of an insulated hand plug 64 co-operating with jacks 20.