The CAT9 is a water cooled external anode power triode with an anode dissipation of 18 kW and an output power of 27 kW when operated in Class C at frequencies below 20 MHz. The CAT9 has a pure tungsten filament and due to the high operating voltage is hard pumped and not gettered.
These valves found use in many BBC transmitters. In the Marconi 100 kW SWB 18 senders at Daventry a pair formed the penultimate PA stage feeding a CAT14 (in later years CAT17 and finally CAT27). The CAT17 weighed 91 kg and stood over a metre tall.
The top of the re-entrant glass envelope. It was normal to blow air at the filament seals to limit the operating temperature. The top anti-corona ring is clamped to the glass. The grid connection is the side terminal.
The lower anti-corona ring is hollow and forced air is directed through small holes at the Housekeeper glass to metal seal to cool the junction.
The valve is operated vertically with the anode encased in a water jacket. The valve is secured via the thread in the brass anode extension.
The holes in the anti-corona ring can be seen near the top of the image. In the centre of the picture is the grid support and the grid rod support ring as it enters the anode cavity. The grid looks to be a cylindrical cage of vertical rods.
This picture has been taken looking down from the filament connections to the filament seals.
The Housekeeper seal. An alloy of 50:50 iron to nickel that had an expansion coefficient to match the glass used was brazed onto the copper anode. The surface of this cone was copper plated and copper oxide will wet the molten glass and form a complete seal. The expansion coefficients matched over a wide range of temperatures thus making the Housekeeper seal both efficient and long lasting. M-OV found that their CAT range were so reliable at the 10,000 hour mark that eventually they offered a guarantee.
A close-up of the top of the grid cage showing the wires attached.
The wide glass tube envelope is 100 mm in diameter, and excluding the base pins is 790 mm tall.