[volt-nuts] Fluke 335A versus HP 740B

Christopher Brown cbrown at woods.net
Sun Dec 16 20:51:59 UTC 2012

On 12/15/12 1:28 AM, Charles P. Steinmetz wrote:
> The main problem today with the HP is that it uses impossible-to-find 
> batteries.  Not only are the original batteries unobtainable, I have 
> yet to find a satisfactory replacement strategy.  It also does not 
> have a +/- 1 uV range, although I do not count that as a major fault 
> since thermocouple noise in the measurement setup frequently prevents 
> taking full advantage of the 1 uV range.

Not a 419A expert by any means, but I happen to have 3 I picked up at
parts prices and am repairing the newest of them.

The oldest has a oval 3 pin AC connector.

A newer one has a standard IEC socket.

Both of these have 3 battery packs made of some form of coin cell, NiCd,
225ma, 5 to a stack.

I found some 60ma similar cells in current production (at least in
china), but the right stuff has been impossible to find.

The newest 419 is different.  Different battery holder, and uses 4 packs
of 5 1/3AA cells.  These are not common, but are not that hard to get.

I also found ref in one of the manual change sheets about a different
battery holder.

Now, converting an older unit would not be hard.  The only thing diff is
the mount and the packs themselves.

Take a couple pieces of say 1/2in thick delrin, cut to about 2"x4"
(measure the space).  These mount to the same screw holes as the
original clamp mount.  Cross drill 4 holes for the packs, and stretch a
couple 0-rings around the packs once in.  This is what the newer
mount/pack from the factory is like...  Two flat plates with 4 cross holes.

Anyway, the older coin cell 419s are pretty badly damaged due to leakage
from the packs, am tearing them down for parts.  The newer one didn't
leak, am just shopping for 20 good tabbed 1/3AA cells.  Solder 5, inline
shrinktube, repeat 4 more times and done.

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