by Norm Wilson N6JV – Visit the museum at N6JV.com
8011 (The Micropup)
In 1940, the British were just holding their own in the Battle of Britian. The outcome was not certain as their cities were being flattened by the Luftwaffe and the German “U” boats were stopping much of their shipping. Nations don’t like to share their top secrets with even their best allies, but if they lost, their allies could use their research and possibly stop the Axis.
A delegation under the leadership of Sir Henry Tizard, sailed to the United States with a collection of equipment they wished to share with the United States and Canada, They met at the Massachusetts Institute of Technology (MIT) and shared their “Holy Grail”, the cavity magnetron, and some other equipment including a working RADAR system that would allow a plane to find surface ships and “U” boats in any weather. The British were hoping to trade for the Norden bombsight. It was decided to form a new working group to conduct research. This became the MIT ”Radiation Laboratory” or just the “Rad Lab”.
The RADAR was the ASV (Air to Surface Vessel) Mark 11. Its development started in 1937 and it had been successfully deployed against a “U” boat. The transmitting pulsed oscillator used a pair of British VT90 valves that had an output of 7 kW at 175 MHz. Copies of the VT90 were made by each country. The 8011 was the RCA version. The Canadians made the REL1 and Western Electric made the WE710A but all were interchangeable. The sets were basically the same and the US sets were designated ASE/SCR-521. The Canadians alone made 10,000 units. A search aircraft could spot a destroyer or submarine at about 20 miles using the Mark II. Larger vessels could be spotted up to 35 miles.
The 8011 operated with 9 kV on the plate with a dissipation on 100 watts. The filament operated at 8.25 volts at 7 amps. The mu of the tube was 15 and the maximum frequency was 600 MHz. Air for cooling was applied to the side of the plate through a notched tube. I have never found the reason they called these tubes “micropups”.
The British had been mounting their Mark II sets in their PBY Catalina flying boats. As new sets were available, starting in Dec. 1940, they were mounted in the U.S. Navy’s PBYs and were an instant success. By the start of the U.S. involvement in WWII, the Mark IIs were widely deployed. The Catalinas played an important role in spotting Japanese ships in the Battle of Midway and the Guadalcanal campaign. The Mark II had a receiving antenna mounted near the end of each wing. Other multi-engine aircraft were used including the B-17 bomber. I have seen photos of B-17s flying long range security for a large convoy traveling to Europe.