[Andrew Sinclair]

Hello,
I have been struggling to repair one of these bridges, but I am now reasonably happy that it is working. Like many WK instruments it uses transformer ratio arms and has a synchronous detector and uses an auto-balance technique. The best manual I could find on the web is a Royal Navy document, BR1771(63) dating from 1967. My instrument dates from 1975, judging by the component date codes, and is the B421 civilian version.
Mine has more modern transistors (BCY70 in place of OC202) and many value changes from the manual I have. The inductance calibration procedure cannot be used with my bridge. I have attached some rough notes for anyone else trying to repair one of these instruments.
Like a lot of WK kit, the design is much cleverer than it seems, and it is a very useful instrument when working properly.
I spoke to a helpful gentleman at WK, and he sent me a manual dated 1973, but it does not have the modifications fitted to mine.
Does anyone have a copy of a more recent manual?
Andrew