phillips@fozzie.nrl.navy.mil (Lee Phillips) (05/01/91)
At a flea market I picked up, for $2, a box manufactured by General
Radio with a meter on which is inscribed "tuned amplifier and null
detector". The box has a coax input and bannana plug outputs. It
is powered by a set of exotically sized electrical cells. It is early
discrete solid state. Anyone know what this is for?
--
Lee Phillips
phillips@fozzie.nrl.navy.mil
phillips@cmf.nrl.navy.mil
phillips@lcp.nrl.navy.milwhit@milton.u.washington.edu (John Whitmore) (05/01/91)
In article <DrPHILLIPS.91Apr30140257@fozzie.nrl.navy.mil> phillips@fozzie.nrl.navy.mil (Lee Phillips) writes: >At a flea market I picked up, for $2, a box manufactured by General >Radio with a meter on which is inscribed "tuned amplifier and null >detector". The box has a coax input and bannana plug outputs. It >is powered by a set of exotically sized electrical cells. It is early >discrete solid state. Anyone know what this is for? In the days of yore, capacitors and the like were measured using RLC bridges. The bridge had a lot of knobs and a little meter. When the knobs were set at the value of the unknown Cx, the meter read zero. Bridges had some nice characteristics; your test frequency could be tuned to the region of most interest (and there was an easy test to see if that foil-wound capacitor was really capacitive at 234 kHz: test it for capacitance at 234 kHz!). They had some not-so-nice characteristics (the knobs had to be tuned two or three at a time until the 'null' meter was zeroed). You could increase the sensitivity by using an amplifier on the meter, or increase the sensitivity a LOT by using both an amplifier and a tuned detector. What you have is the sensitive AC detector that one would use to accurately balance a bridge. It wouldn't be a GR model 1231B, by any chance? John Whitmore