Wednesday, January 4, 2012

HP 331A Distortion Analyzer Teardown

While messing with my RC Wien Bridge Oscillator I noticed I was getting some erratic readings now and then,  so I decided to do a bit of a teardown on my HP 331A Distortion analyzer. I did notice that some of the boards were connected with pins and sockets and they were pretty loose. Grabbing the soldering iron I hard soldered the wires to the boards in hopes my erratic behavior would go away.

Once I put the Distortion Analyzer back together I remeasured my RC Wien Bridge Oscillator Distortion and was getting a very repeatable 0.025-0.030%. I am still off from Jim's 0.0025%, but I think I am really pushing the resolution on this old piece of equipment that was last serviced in 1965 and last calibrated in 1987.

Below are picks from the HP 331A tear down:


  1. I noticed that you also have a Heathkit IM-5258. Did you ever find a schematic for that? I'd really like to see how that devil works -- especially their auto-nulling circuit.

  2. Awesome blow with beautiful images. Thanks for sharing detailed information about Bridge oscillator.
    ECS Crystal Oscillators