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A new type of voltage-tuned microwave oscillator, called the helitron, is described. This device is a practical example of E-type interaction. Electron focusing is accomplished by balancing centrifugal force against a radial electric field force and RF field interaction is both radial and angular. No magnetic field is required. The device employs a spirally-traveling electron beam interacting with the angular and radial components of RF field provided by an internal circuit structure. Experimental results include continuous voltage tuning from 1.2 to 2.4 kmc with an accompanying change in tuning voltage of from 650 to 1700 volts. Start-oscillation current is approximately 0.4 ma for a structure 4 inches long. Power output is in the vicinity of 1 to 10 milliwatts. Second-harmonic output is more than 25 db down, and all other spurious output is more than 60 db below the main oscillation. Possible advantages and limitations of the helitron are described together with brief mention of the accompanying theory of operation.