[volt-nuts] HP 3458A Vref module

Sun Jan 24 05:30:16 UTC 2010

I was able to troll through the archives the other day and saw a post about HP 3458 Vref modules for sale. I contacted the seller listed in the post and he still had some, though he mentioned that a university was looking at buying up his remaining stock. I was able to get one and should have it here around Wed or Thur. Pretty slick way to get something quickly usable to play with. Thanks, volt-nuts!

@Bill re Fluke 510A -- I opened up the 400Hz unit, which was the real drifty one -- it was more than 5000ppm high yesterday! I reset the gain-control FET's bias, set the zero points on the integrator, and adjusted the Vref (had to pad R29 to get the pot in range, even with the A & B jumpers both open). Didn't measure the actual Vref -- will do that if and when it's re-warmed up and seems stable, and report back. Set initial level to approx. +10ppm. Still don't know why it was off so far -- nothing was too far out on the adjustments. Very strange. The 40kHz unit was low by about 70ppm; I got it to about +10ppm and we'll see. THD on the 400Hz unit is about 0.002% and is pretty independent of the FET bias. THD on the 40kHz unit is about 0.01%. The integrator capacitors are Tantalums on these, so after all this time, could have a leaky one....

Dick Moore

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