HP 4260A Universal Bridge

Brooke Clarke, N6GCE, 2003 - 2022

HP 4260A
HP 4260A


My first HP 4260A Universal Bridge has a plate on the top cover that reads:
Bridge, Capactance,-Inductance-Resistance, ZM71A/U, Serial No. 12A, Hewlett-Packard co., PIIN:  DAAB07-82-C-H036, Warranty Thru 02/84, U.S.  So this one was built on a government contract.
This is a manually nulled LCR bridge operating form an internal 1 kHz (or external 20 Hz to 20 kHz) oscillator.  It's packaged in one of the HP "sub modular" sized cases and can be rack mounted.

From the serial numbers it appears this instrument ws made from 1970 through at least 1975.  Maybe this was replaced by the HP 4332 LCR Meter, or maybe one of the digital auto balancing LCR meters in the 42xx model series..

C range 1 pF to 1,000 uF in 7 ranges with D from 0.001 to 50
L range 1 uH to 1,000 H in 7 ranges with Q from 0.02 to 1,000
R range 10 milli Ohms to 10 Meg Ohms in 7 ranges
Accuracy 1% in the center ranges and 2% at the extremes.

What Goes Wrong

This instrument has seen some very rough times.  Looks like it was subjected to an extremely high shock.  

The shaft on the "DQ" control that's attached to the CAL pot was broken.   I'm now trying to find a replacement "DQ" pot or maybe just make a replacement shaft.  This can wait to see if the bridge is operational.

One of the 2 wires going to the main "CRL" pot with the odometer counter attached was disconnected, I think by someone trouble shooting it since it tests open, and not the 5 k Ohms it should be.  Inside the rod that rubs against the resistance wire was disconnected form the wiper and a very fine wire that connected to the end of the resistance wire no longer makes the connection.  May need acid flux or silver epoxy to get a good joint.  The plastic that supports the resistance wire had numerous radial cracks all the way though, these were fixed using acrylic cement.


There are many more Japanese and English patents assigned to Yokogawa HP

JPS61276400 Shielding case, Kazu Suzuki, YHP, 1995-01-30, - to new to apply to the LCR meter
3274501 Voltage to frequency converter, Edward A Heinsen, HP, 1966-09-20, - Heinsen in mentioned in the HP Journal article.
3377603 Slide rheostat having linearity adjustment, Suzuki Kazu, YHP, 1968-04-09 - requires manual tweaking - just the think for an LCR meter
3474334 Automatic nulling measurement bridge using double phase angle detection, Giichi Yokoyama, Toshio Muraoka, Hitoshi Noguchi, YHP, 1969-10-21, -
3947760 Integrating component measuring device, Hitoshi Noguchi, Kohichi Maeda, Takeshi Kyo, HP, 1976-03-30, - dual 5-digit displays, beginning of 4-terminal pair?

4841228 Apparatus for indicating the resistive characteristic of a capacitor, Hitoshi Noguchi, Hideki Wakamatsu, HP, 1989-06-20, - ?


HP Journal September 1966 - This may be the first HP impedance instrument from Japan.

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