amplitron

A crossed-field amplifier (CFA) is a specialized vacuum tube, first introduced in the mid-1950s and frequently used as a microwave amplifier in very-high-power transmitters. A CFA has lower gain and bandwidth than other microwave amplifier tubes (such as klystrons or traveling wave tubes); but it is more efficient and capable of much higher output power. Peak output powers of many megawatts and average power levels of tens of kilowatts can be achieved, with efficiency ratings in excess of 70 percent.
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amplitron