Triode RD70VL

Evaporation-cooled triode for frequencies up to 100 MHz, 14 V / 260 A heater, 15 kV maximal anode voltage, 70 kW anode power. Three of these tubes, connected in parallel, were used in the high-frequency output stage of the Dobrochov medium-wave transmitter, which operated until 2021. The anode of the tube is submerged in cooling water, which is boiled by the tube's waste heat. The water vapour is run into a cooling system, condensed and reused. Evaporation takes up much more heat than simple liquid cooling, so the water flow can be much lower. The system has to be designed in a way that ensures no bubbles will form on the surface of the anode, otherwise the anode would overheat immediately. Due to this, any detergents were strictly forbidden from use for cleaning of the cooling system. To provide insulation, distilled water had to be used, as it was in direct contact with the anode, which was on high voltage potential. Distilled water is electrically non-conductive.