641,342. Electric resonators. SPERRY CORPORATION. Aug. 2, 1944, No. 14799. Convention date, Aug. 11, 1943. [Class 40 (viii)] [Also in Group XL (a)] High-frequency electric discharge apparatus comprises one or more hollow resonators having relatively movable wall portions and a bimetallic tuning strut interposed between extensions of said wall portions. In the construction shown in Fig. 1 the volume of the resonator 21 having a flexible annular wall portion 26, and the spacing between the grids 27 and 28 is controlled by a plurality of adjustable threaded sleeve members 34 within which are rod members 38 extending between a threaded apertured ring 32 secured to an annular flange 31 on the evacuated envelope 12 and an annular flange 15 secured to the wall 14, equally spaced tension springs 53 being connected between the flanges 15 and 31. Coarse adjustment of the volume and the grid spacing of the resonator 21 is effected by rotation of the sleeve 34 in the ring 32 by means of the slot 51, and fine adjustment of one sleeve and rod device is effected by the micrometer screw 45 acting on the lever 42 fulcrumed on a pair of hard steel projections 44 on flange 15 and having a conical depression 41 in which is positioned a rounded tip 39 on the lower end of rod 38. The other sleeve and rod controlling devices are formed without the fine adjustment means as shown in Fig. 2. The sleeves 34 are .formed of a metal or alloy having a low coefficient of thermal expansion such as one of the ferrous alloys known under the Registered Trade Marks " Invar," '' Kovar " and " Nilvar." The rods 38 are made of a metal or alloy having a very high coefficient of thermal expansion such as the alloy known under the Registered Trade Mark " Duralumin," the arrangement reducing changes in the volume and grid spacing of the resonator 21 due to changes in ambient or operating temperatures. The sleeve 34 may bo rigid or integral with flange 31 and Fig. 4 shows such a sleeve 67 having a rotatable end plug 68 threadedly mounted in its upper end and formed with a slot for adjustment. In the construction shown in Fig. 5, coarse tuning is effected by rotation of screw 73, and large thermal expansion of " Duralumin " rod 72 effects compensating tuning for eliminating frequency drift due to temperature variations. Effective shortening of the strut when ambient temperatures fall below a predetermined value is limited by the hollow sleeve 79 loosely resting on flange 15 and terminating short of the closed end of sleeve 69. Sleeve 79 is made of an alloy such that it has substantially the same high coefficient of thermal expansion as the strut for temperatures above a selected value, e.g. 0‹ C., but has a far lower coefficient for temperatures below the selected value. Alternatively, the rod 72 and/or screw 73 may be made of materials which accomplish the function of sleeve 79 by slowing or stopping the strut contraction, e..g. exponentially, at the selected low temperature. In a further construction provision is made for regulating the effective length of the high thermal expansion part of the tuning strut. Specifications 535,767, 582,487 and U.S.A. Specifications 2,261,154 and 2,294,942 are referred to. The Specification as open to inspection under Sect. 91 describes the invention as applied to hollow resonator devices having two or more resonators such as buffer oscillators and frequency multipliers. In the construction shown in Fig. 7 (Cancelled) an electron beam from cathode 81 is projected through spaced grids 82, 83 of input resonator 84, along drift tube 85 and then through spaced grids 86, 87 of output resonator 88. A radial flange 89 is rigid with drift tube 85 and similar flanges 91 and 92 are rigid with resonators 84 and 88. Drift tube 85 is flexibly connected to resonators 84 and 88 by flexible end walls 93 and 94. A plurality of equally spaced thermal compensating independent compound tuning struts 95, 96 as previously described are interposed between flange 89 and flanges 91 and 92 respectively, biassing springs similar to those at 53 in Fig. 1, but not shown, being employed. In the construction shown in Fig. 8 (Cancelled) electron beam from cathode 97 is projected through spaced grids 98, 99 of input resonator 101, along drift tube 102 and through spaced grids 103, 104 of output resonator 105. Manual tuning adjustment of the resonators is effected by threaded struts 113 and associated nut pairs. Thermally responsive frequency regulation is effected by making the walls 123 and re-entrant pole 124 of resonator 105 of " Kovar " or other material having a low thermal expansion coefficient, resonator 101 of copper having a higher coefficient, and tuning strut member of a section 125 of e.g. stainless steel having a high coefficient and of a rigidly-joined section 126 of e.g. " Nilvar " or " Kovar " having a low coefficient. Strut sections 125 and 126 may be replaced by compound strut sections similar to those shown in Fig. 2. Fig. 9 (Cancelled) shows a compound strut for use in the device shown in Fig. 1 comprising a sleeve 128 of " Kovac " threadedly mounted in apertured flange 31 and a threaded rod 129 of " Duralumin " supported in the closed end of the sleeve.- Lock-nuts 132 and 133 are mounted on rod 129 for coarse tuning and a lock-nut 134 protected by cap 135 is provided for altering the effective strut length. A lock-nut 136 holds the sleeve in axial adjustment. The various strut constructions may be interchanged. Specification 531,067 and U.S.A. Specifications 2,250,511, 2,281,935 and 2,311,658 are referred to. This subject-matter does not appear in the Specification as accepted.