For high linearity, high gain and greater isolation, the tetrode is the tube of choice. Many manufacturers offer tetrode design transmitters to meet increasing power needs. In fact, tetrodes are the primary means for achieving power levels above 1 MW. Shortwave transmitters, including those broadcasting in Digital Radio Mondiale (DRM) format, turn to Eimac products from 100 kW to 1 MW. While a mainstay in AM, FM or TV broadcast transmitters; tetrodes are being used today in high power RF heating systems where the designer uses a separate oscillator driver to attain tight frequency control. Air-cooling is used with plate dissipation ratings of up to 40 kW; while water, vapor-phase and multi-phase cooling is used above 40 kW. Richardson Electronics offers the world's largest selection of power tetrodes from stock for names like CPI-Eimac, Amperex, Thales, BURLE, and National Electronics, as well as rebuilt product from CPI-Econco.