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The term "platinotron" is the nomenclature given to a class of tube which, in general, comprises a circular, but nonreentrant, dispersive network matched at both ends over the frequency region of interest, and a reentrant electron beam originating from a continuously or nearly continuously coated cathode coaxial to the network. A dc potential is applied between the cathode and anode and a magnetic field is applied parallel to the axis of the cathode and transverse to the electric field between anode and cathode. In operation, the device works within the pass band of the network and exhibits directional properties, acting as an efficient, broadband, saturated amplifier when the signal is passed through the device in one direction and as a passive network when the signal is passed through in the reverse direction. The platinotron has no region of linear amplification and may self-oscillate if the driving signal is removed. When the platinotron is being driven from an rf source, there is little or no power flow from the platinotron toward the driver. This behavior distinguishes the device from a conventionally locked magnetron oscillator. Desirable characteristics of the platinotron include: efficiencies of 50 to 70 per cent; high peak and average rf power outputs, electronic bandwidths of 10 per cent with nearly constant efficiency over the entire bandwidth, low-phase pushing figure, low operating voltage, nominal gain of 10 db over a ten per cent frequency range, and a simple, compact mechanical structure.