ABSTRACT There are two important problems that arise in the use of amplitrons, as broadband microwave amplifiers in high power radar systems with frequency agility. The first one is to modify the conventional high vacuum tube modulator to obtain proper operation with good efficiency in case of very high power levels. The second one is to modify the modulator circuit by increasing its output impodance and thus limiting the poak current variations in the transmitted frequency band. In this paper analyses are made of both these problems, some practical results are given, and the implication in actual transmitter design is examined.