David:

I bought a Valhalla 2734A in June of 2003 for $270.  I soon found out that it wasn't as stable as Valhalla would like you to believe.  It does meet specs but week to week stability is around 0.5 ppm, up and down.  The Fluke 732A is much more stable on a week to week basis.  I found this out after buying a few 732A's.

A few years back I opened the 2734A up and looked inside the ovenized reference.  I remember seeing it using 4 each 1N827 (or something close to that) zener diodes.  Then there was an opamp for each diode to raise the 6.2 volts of the zener up to 7 volts and allow adjustment to exactly 7 volts.  Then these 4 opamp outputs were being summed into another opamp that raises the total to 10 volts and allows adjustment to exactly 10 volts.  All of this was inside of an oven that was running at around 45 degrees centigrade.  It seemed very room temperature sensitive and there was no insulation around the oven assembly so I added some insulation around the oven to try to help this problem.

I kept looking for a manual, as Valhalla won't even acknowledge that they ever made this instrument.  I finally found one from Tucker Electronics for $25.  The manual does not show anything about the reference board assembly and tells you to replace this item as a unit.  They do tell you how to adjust the instrument.

I think that the 732A is a much better instrument.  I can scan in my manual if you need it and email it to you as a pdf.  I can't scan "B" size prints so I would have to break these into 2 pages.

Bill

Hi

Sounds like the Valhalla is a candidate for a LM399 or LTZ1000 transplant if you can get one at the right price. As others have shown an ovened "plain" zener can work, but only if you test, burn-in and test again to find the good ones and adjust the current for the individual diode. Sounds like Valhall went for the statistical approach.

Robert G8RPI.

From: Bill Gold wpgold3637@att.net
To: volt-nuts@febo.com
Sent: Sunday, 19 August 2012, 0:50
Subject: Re: [volt-nuts] Valhalla 2734A

David:

    I bought a Valhalla 2734A in June of 2003 for $270.  I soon found out that it wasn't as stable as Valhalla would like you to believe.  It does meet specs but week to week stability is around 0.5 ppm, up and down.  The Fluke 732A is much more stable on a week to week basis.  I found this out after buying a few 732A's.

    A few years back I opened the 2734A up and looked inside the ovenized reference.  I remember seeing it using 4 each 1N827 (or something close to that) zener diodes.  Then there was an opamp for each diode to raise the 6.2 volts of the zener up to 7 volts and allow adjustment to exactly 7 volts.  Then these 4 opamp outputs were being summed into another opamp that raises the total to 10 volts and allows adjustment to exactly 10 volts.  All of this was inside of an oven that was running at around 45 degrees centigrade.  It seemed very room temperature sensitive and there was no insulation around the oven assembly so I added some insulation around the oven to try to help this problem.

    I kept looking for a manual, as Valhalla won't even acknowledge that they ever made this instrument.  I finally found one from Tucker Electronics for $25.  The manual does not show anything about the reference board assembly and tells you to replace this item as a unit.  They do tell you how to adjust the instrument.

    I think that the 732A is a much better instrument.  I can scan in my manual if you need it and email it to you as a pdf.  I can't scan "B" size prints so I would have to break these into 2 pages.

Bill

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