Triode ZD1000F

Radiation-cooled triode, best suited for modulators. 7,5 V / 34 A filament, 60 MHz top frequency, 4 kV maximal anode voltage, 1 kW anode power. The anode is cooled in the same way as in small vacuum tubes for household radios - by thermal radiation through the glass. But with the 1 kW anode loss, the technology is pushed to the limit. The anode was red hot during operation, the glass bulb and the electric terminals also got very hot and the glass could easily break if improperly installed. These tubes were used in the Liblice and Topolná transmitters as the first stage of the modulator. While all the other tubes, used in these transmitters, had a ceramics envelope and were enclosed inside a cooling system, these tubes were made of glass and could be directly observed during operation. The red hot anodes were thus often photographed by the few visitors who were lucky enough to be allowed to see the transmitters in operation.