The problem involved in this thesis was to construct a source of microwave frequency electromagnetic energy to be used as the signal source of a microwave maser. The maser was intended to have a signal frequency of 9 - 10 kmc. and a pump frequency of 22 - 25 kmc. For this purpose it is necessary to have a signal source whose frequency is accurately known and will remain constant. The frequency-stabilized source constructed made use of a reflex klystron and a Pound discriminator. The components of the system, the klystron, the discriminator, and the amplifier, are analyzed and their calculated and actual performance presented. It is shown that the Pound discrimiator can be made more sensitive by allowing its crystal detectors to have unequal sensitivities, instead of the usual practice of equalizing their sensitivities. The actual performance of the system in stabilizing the frequency of oscillation is presented and compared with the expected requirements of the signal source of a microwave maser. The system was found to provide a frequency stability of 5 parts in 106, which will in general be adequate for the intended purpose.