[Test-Equipment] Bridge Parts

[k2cby]

Three suggestions:

First:     Don’t change anything. I looked at the schematic and it appears
you can use an external 
            generator as the signal source. Use one set to 50Hz and you’re
in business.

Second:  As the old saying goes, you’ve got the keys to the jail in your
pocket. 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%.

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).
            

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400
Fax.: (631) 725-2223
e-mail: k2cby at optonline.net