AV11

The AV11 is a high-vacuum half-wave rectifier developed in Australia during the Second World War for radar high-voltage supplies. Colin MacKinnon's account, published in 1994 and based on Radiophysics Laboratory reports, places its development amid the supply crisis of late 1940 and early 1941. The laboratory was adapting the British ASV Mk II radar for ground use and sought greater pulse power than the original system's approximately 6 kW; a supply of about 10,000 V was required. These figures describe the radar and its supply, not the rectifier's power. AWV, Amalgamated Wireless Valve Co., part of the Australian AWA group, began the project after receiving the government order.

The filament requires 2.5 V and 1.75 A. The article gives provisional specifications of 14,500 V peak inverse voltage, 30 mA maximum average plate current and 350 mA maximum peak plate current. The later experimental comparison table instead lists 5000 V RMS AC plate voltage, 12,500 V peak inverse voltage, 300 mA peak current and 30 mA DC output for the AV11. These are different contexts that must remain separate: RMS AC voltage, peak inverse voltage and DC voltage are not interchangeable quantities. The comparisons also involved RCA 2X2/879 and Mazda V.1907 valves, without constituting a statement of equivalence between those types.

Testing began in January 1941 and continued to the end of February. The first two specimens showed residual gas, blue glow and filament failures even at low voltage; subsequent versions allowed high-voltage testing. It was found necessary to switch on the filament about 30 seconds before applying high voltage to prevent destructive flashover. A time-delay relay was therefore introduced in the radar equipment. An interesting detail concerns the initial request for a very severe test on every valve: AWV objected that such testing risked using up the item in the very act of proving its reliability. A request followed for a guaranteed 1000 hours at 14,500 V peak inverse voltage and 30 mA average current, together with a five-minute test at 21,000 V peak inverse voltage and 40 mA. These were historical qualification requirements, not a guarantee of remaining life for surviving specimens.

The construction uses the same envelope and top cap as the AWV-produced 807, but with a different function and internal structure. The horizontal W-shaped filament is supported by five wires; its two ends connect to pins 1 and 4 of the four-contact base, called USM4 in the article. The plate, connected to the top cap, consists of two flanged half-shells welded together and supported by four glass rods; it surrounds the filament with approximately 5 mm clearance. The account states that the AV11 was accepted for production and several thousand were made for ground and airborne radar. Documentary source: Colin MacKinnon, The AWA AV11 Rectifier, H.R.S.A. Radio Waves, October 1994, pp. 3–4; the article cites Radiophysics Laboratory reports RP57/1, RP72/1, RP72/2 and RP72/3.