[Test-Equipment] Bridge Parts

[Barry]

> Second:  As the old saying goes, you’ve got the keys to the jail in
> yourpocket. This is a capacitance bridge, 
> so just get a bunch of high quality mylar capacitors close to
> .02 µF and .04 µF and measure them 
> on the bridge at 50 Hz (or measure at 60 Hz without using the
> auto-null feature) until you find one within 1%.


Well, that would be great if the bridge was working but it isn't.  That's why I've been into it in the first place.


> Third:    The frequency-critical circuit in the detector is a bridged T
> designed so that C411 and C412 each have a 
> reactance at the operating frequency (131k) twice the resistance
> R422 and R423; and C413 has a 
> reactance (67k) of twice the resistance of R424. 
> 
> You can get the same result for 60 Hz by leaving the 50 Hz
> capacitance values in place and 
> changing R422 and R423 to 54,580 (closest 1% value is 54900) and
> changing R424 to 27,922 
> (1% value = 28000).


Cool!  I didn't know what that part of the circuit does but that's a great idea.

Thanks again,
Barry - N4BUQ