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A commonly used method is described for obtaining crystal control of high-frequency transmitters from crystals of lower frequency by means of a frequency multiplying vacuum-tube amplifier. An experimental study of the operation of the system is made when doubling and tripling the frequency of a 4000-kc crystal-controlled oscillator, and comparisons are made with the operation of the same system when balanced and amplifying the fundamental frequency. Relations between d-c negative grid voltage and r-f input voltage for maximum efficiency are shown to be critical and nearly constant for any one order of multiplication. Satisfactory operation of the system is shown to depend upon inductive reactance in the grid circuit, which produces regeneration through the grid-plate feed back in the tube. The study is based on circuit efficiencies as measured by the contact pyrometer method.