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A number of recent developments have contributed to the design of multiplier phototubes having improved time discrimination, as well as improved pulse-height resolution. In the 6810-A, a modified version of the first commercial high-gain, high-speed tube, a curved faceplate (flat on the outside) is used to reduce transit-time variations in the region between the photocathode and the first dynode. Special geometrical construction is used to minimize transit-time spread in the 7046, a five-inch tube developed under an AEC contract. Curvature of the inner faceplate is also used to improve pulse-height resolution and time discrimination of developmental versions of the 6342 and the 6655. In a new developmental tube, RCA Dev. No. C-7251, cathode curvature is combined with a new electrode structure between the cathode and the multiplier structure to reduce transit-time spread to less than a few tenths of a millimicrosecond.