[volt-nuts] HP 735A DC Transfer Standard

[R.Phillips]

Hi Bill
Well I suppose I should have guessed it - Fluke are probably the # 1 when it 
comes to DC 'Standards'  I had never encountered an HP-735 before and this 
one is in overall good condition - I will complete the restoration and keep 
it as a 'collectors item (its not too big!) As for the fluke range, I have 
two 731B's and better, a Fluke 732A which has been running non-stop for more 
than a year - it now reads the same on my HP 3458A , which is still in 
calibration. I agree that the Fluke 731B is a good standard for its size, 
pity about the 'poor' battery back-up circuitry, and the NI-CADs which have 
damaged so many. The other shortcoming was the rotary switch - it would have 
been better with a set of terminals for each range.
Regards
Roy


From: wb6bnq
selection
-----Original Message----- 
Sent: Monday, May 18, 2015 10:29 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] HP 735A DC Transfer Standard

Hi Roy,

I hate to tell you but the hp-735 does not compare to the Fluke 731.
The hp-735 had a drift that was constant.  This information came from a
friend of mine that was responsible for the US Navy's Primary DC voltage
standard at their Primary Lab in San Diego, CA in the 1970's.  The
actual drift rate I do not recall anymore, but it was significantly
higher than the any drift in the Fluke.

Bill....WB6BNQ

R.Phillips wrote:

>
>
> -----Original Message----- From: gilbenl at nickgilbert.org
> Sent: Sunday, May 17, 2015 4:13 AM
> To: volt-nuts at febo.com
> Subject: [volt-nuts] HP 735A DC Transfer Standard
>
> Recently acquired a HP 735A DC Transfer Standard. Replaced some caps, but 
> its otherwise clean and has since been powered. Read a post recently about 
> a 735A oven failure that included a teardown that revealed why HP states 
> the oven/ref assembly a non-serviceable part. The failure in this person's 
> device was the heater, specifically the thermistor.
>
> Anyone on this board have a 735A in use? Do you keep it powered 24/7 or 
> as-needed? Any failures/repairs/mods?
>
> Best
> Nick
> ______
>
> Hi Nick
> I also very recently  acquired a HP 735A DC Transfer Standard. Mine has a 
> Power Transformer with the centre tap 'open circuit' - this I guess was 
> the result of a failure in the pre-regulator circuit which in turn caused 
> a resistor to 'burn-out'. I have 'hooked-up' external positive and 
> negative rails and the unit works, including the oven !  So, I will 
> rebuild this to the later and I think final specification - which 
> eliminates the 'pre-regulator' circuit. Otherwise the unit is in excellent 
> condition, in keeping with HP of that period, and probably superior to the 
> Fluke 731B. I gather that these are quite rare items now. Let us know how 
> you get on with the 'project'
> Regards
> Roy Phillips.
>
>
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