653,243. Control systems for consumption apparatus. BUDD CO. June 5, 1947, No. 14847. Convention date, June 14, 1946. [Class 38 (iv)] Thermionic (and like) control.- The current in an A.C. welding load circuit, which is interrupted by a device 25 upon abrupt voltage change at the weld point upon weld fusion, is progressively varied during the period of application by automatic shifts of the phase of the grid potentials of valves 11, 12 controlling the firing instant of a pair of backto-back ignitrons 9, 10 in the load circuit according to the potential across a charging or discharging condenser so as to vary the fraction of successive half waves of the load current. The phase shift is effected through a transformer 35 included in an A.C. bridge 30 which has included in one arm the A.C. winding 34 of a saturable choke, the D.C. winding 36 of which is supplied with current through valves 39, 40, the grid potentials of which are dependent on the potential across a condenser 59. To obtain a progressive increase in load current a falling grid potential to valves 39, 40 is derived from a D.C. bridge 54 comprising two parallel arms, each having respectively a constant potential discharge device 65, 68 and a resistance 66, 67 and reversely connected, with a potentiometer 69 connected between the functions of the discharge devices 65 and 68 and associated resistances, the slider of which is connected to valve grids 41 and 42 ; connection to the cathodes of valves 39, 40 being made through a potentiometer 73, in series with a resistance 72 shunted across the discharge device 65. The D.C. bridge is energized during the non- welding period from a rectifier 46. When the welding period is initiated by valve 16 a relay 19 opens contacts 53 and 58 and closes contact 60 so that the bridge is then energized by a precharged condenser 59 thereby providing a falling potential to grids 41 and 42. Progressive decrease in the load current during the post-weld period, for annealing the weld, is provided by the circuit shown in Fig. 2 which is substituted between the terminals 95, 96, 97 and 98 in Fig. 1. The grids 41, 42 are normally maintained at a potential corresponding to that existing between points 90 and 94 and upon initiation of the post-weld period, contact 84 is closed resulting in the potential across the condenser 90a increasing to that across points 86 and 94 at a rate determined by the setting of resistance 93. This latter circuit may also be used to obtain the progressive increase in load current by arranging for the contact to be normally closed but opened upon initiation of weld period and thereby provide a decreasing potential to the grids 41 and 42. The device 25 (Fig. 1), may be as described in Specifications 606,958 and 642,468, and may be supplemented by a timing circuit comprising a valve 17 which disconnects the load circuit after a predetermined number of cycles in the event of the device 25 not operating within this period.