ECH21 Telam is a heptode - triode tube with indirectly heated oxide cathode. Both systems are working separately, cathode is common for both of the systems. Heptode may be used as a mixer, hf or lf amplifier. Triodes like oscillator or lf amplifier. ECH21 was a part of many old radio receivers (for example Tesla Riava, Signal, 506A Arie, 619A Dalibor, 620A, 623A Máj, 621A Opera and many others). New in box tubes. Tested.