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HP-8590A Mixer Diodes

Question asked by LarrBeard on Nov 14, 2011
Latest reply on Nov 25, 2011 by k2ue
I end up learning more and more about the HP-8590A even though I don't start out on a voyage of discovery.

Now that I have found a source for a replacement attenuator module for the unit, it turns out that most units with blown-up attenuators have damaged First Mixer diodes.  The AMPLITUDE CAL routine does wonders to compensate for excessive conversion loss, but if you look in enough places, you find out that things just don't work right.

The First Mixer is very similar to the A4 module in the 8558B.  That mixer uses a pair of matched diodes (A4U1) as the non-linear mixing element.  The original HP P/N was 08558-20095, later changed to 08558-60152.  Neither part is still in HP support.  The 8590A A4U1 was P/N 5062-0785.  Same status.

But, my guess is that the diodes were selected from a diode family that had another P/N.  They might have been 1N5712's, or HP-5082 series parts.  Does anyone have any insight into just what these diodes were?