[volt-nuts] Fluke 731B parts xref

Christopher Brown cbrown at woods.net
Thu Nov 22 05:56:30 UTC 2012

On 11/21/12 6:44 PM, WB6BNQ wrote:
> Hi Chris,
> Do you mean the Fluke 750A ?  It has connections for standard cells.  The 752 is a ratio
> device designed to be used with a 10 volt reference standard.  No need for the 1.xx outputs
> from the 731B or the use of standard cells..

Your are correct, not the 752 (would like a 752 and a 720) but do have 2

> The 750A standard cell arrangement can be bypassed and set up for use with just a 10 volt
> reference using the original banana jacks for the reference and null meter as normal.  All
> that is needed is to (non destructively) remove one connection and add one wire.
> Bill....WB6BNQ

That sounds like a very worthwhile mod.  How is it done and how does it
change operation?

As far as the 731B(s), I have 2.

One is in good working order and overall great shape.  Came out of a
standards lab in the czech republic that recently switched to a 732A.

Have a replacement NiCd pack currently cycling.  Other than cleaning,
and replacing the dead pack the only changes planned are replacing the
IEC socket with a small filtered socket (have a box of them) and
replacing R30 (if needed) to adjust the float current for the new pack
(old is 450mah, new is 2100mah.

For the second (received this morning), intend to do the same, and
repair.  I may just hard-wire around the failed switch, but beyond that,
not fixing it would just bug me.

The ref board is in good shape and does not appear to have been messed
with.  The main issues being the pot and the P/S section.

Near as I can tell the Fairchild 1N5248B is a good match for CR1, and
for 2 cents each I can just grab a batch and select.

I have a bunch of 4148 and 1n914 fairchild parts around here somewhere,
curious as to suggestion of 4448 over 4148?  Looks like 2pf v.s. 4pf and
the 4148 may start conducting a few hundred mv earlier from the datasheet.

Chris - WL7CLA

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