|
In the UK the commercial EF91 appeared around 1948, however, the CV138 had been used in WWII radar equipment and was developed in about 1944. as John Wilson explains here.
The B7G base originated in America in 1941 as a 'button base' where pins were sealed into a hard glass base and the electrodes connected directly to the internal ends of the pins. The construction thus mirrors developments in the late 1930s in several places. The earliest was probably the RCA metal valves of 1935 but the M-OV Catkins of the early 1930s did not use a pinch. The Footless valves from Europe and the B9G base of the EF50 originated in the late 1930s as did Sylvania's Loctal valves. The drivers for these developments were a quest for efficiency at ever higher frequencies and an reduction in material and production costs.
John Randall writes that he has acquired a RADAR IF strip from a WWII airborne RADAR set probably an ASV Mk15. This is an RU Type 196, serial number 0198. It has ten valves: 1 CV417, 8 CV138 & 1 CV140.
John comments: these images were taken after some components were replaced. The resistors are new, all the originals were way out of tolerance. They all had to be replaced, along with all paper 0.001 μF & 0.002 μF decoupling capacitors. Finally, the RF chokes were all o/c and corroded and so too had to be renewed.
Screening I found is important, when feeding in a signal, the valve cans and the bottom cover had to be fitted.
| 