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

-----Original Message-----
From: gilbenl@nickgilbert.org
Sent: Sunday, May 17, 2015 4:13 AM
To: volt-nuts@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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