CV789

CV789 is an RF power triode of the 3C24 family, recognizable by its top anode connection and side grid terminal. English Electric’s March 1970 sheet, headed 3C24 (B1109), explicitly lists CV789 among service types and CV2736 for matched pairs. It describes a naturally cooled tube for amplifiers, oscillators and modulators, with 25 W maximum anode dissipation and full ratings up to 60 MHz. The sheet’s date identifies that documentation edition, not the year CV789 was introduced.

The directly heated filament is thoriated tungsten and requires 6.3 V at 3 A. The base is small UX4: pins 1 and 4 supply the filament, while 2 and 3 are unconnected; grid and anode use the side and top leads respectively. The sheet specifies vertical mounting, base up or down, and large-area connections capable of dissipating heat from anode and grid. The photographed specimen shows a cylindrical anode formed from deeply corrugated sheet, the grid cage and helical filament; the retained description relates the anode folds to heat dissipation. Cooling and external connections are thus part of operation, not merely appearance.

For Class C RF telegraphy, the English Electric document gives absolute maxima of 2000 V anode voltage, 75 mA, 25 W anode dissipation and 7 W grid dissipation. Typical points are separate from these limits: at 1000 V, −70 V grid bias and 72 mA anode current it lists 47 W output with 1.3 W drive; at 2000 V, −130 V and 63 mA it lists 100 W with 4 W drive. The 100 W is RF output under those conditions, not anode dissipation. Eimac sheets likewise list 47, 75 and 100 W at 1000, 1500 and 2000 V, but editions specify different bias and drive figures, which must remain within their respective data sets.

Modulation requires different figures. For Class C anode modulation up to 100%, English Electric specifies carrier-condition limits of 1600 V, 60 mA and 17 W anode dissipation; the 1000 V example gives 47 W output with 3.3 W drive. This differs from the preceding telegraphy point despite identical output power. The same sheet includes Class AB2 audio-amplifier and modulator service: a pair at 1000 V is listed at 85 W output into a 17 kΩ anode-to-anode load. An interesting family detail is Eimac’s description of 3C24 as corresponding to 25T apart from the side location of the grid terminal; this similarity does not remove the need to check mounting, connections and the actual type specification.