[time-nuts] A HP738BR experience - Was: HP quality... a HP5065Aexperience

WB6BNQ wb6bnq at cox.net
Sat Sep 10 23:56:00 UTC 2011

Hi Bob,

I also have one of those and its companion Frequency Response test set; hp-739.
The attenuator is strictly a high impedance device designed to look into 1
MegOhom or more.  Aimed at high impedance meters and scopes.  Quite stable for
the "day," but could be improved by changing out the Vref tube with a modern
zener, like a TL431, in a scaled circuit to provide the proper voltage

I would keep it in tact.  Nothing wrong with tube technology.  I will email you a
738 manual in PDF.


Bob Smither wrote:

> J. Forster wrote:
> > That is not a unique incident.
> >
> > I'm interested in LASER Interferometry. Attached is a pic I took of an HP
> > 5529A LASER head.
> >
> > (Aside: If anybody is interested, there is a Yahoo Group for LASER
> > Interferometer fans)
> >
> > Note the two leads to CR5 near the top, center of the pic. They go to a
> > feedback photocell and obviously have never been trimmed or soldered.
> >
> > The unit ran fine that for several months before suddenly failing.
> > Soldering the leads fixed the LASER head.
> It was not always this way.  Today I stumbled on a 1965 HP 738BR
> Voltmeter Calibrator at my favorite surplus electronics store.  I
> offered $20.00 and it was accepted.
> This unit is based on vacuum tubes!  I got it home, plugged it in, and
> it is still in spec on the DC range.  The AC part is not working - I
> suspect the small incandescent lamp that stabilizes the oscillator.
> I may end up junking the vacuum tube half.  The other part of the
> instrument, in a separate compartment, has a precision 40 step
> attenuator with a 10^6 / 1 range (300 Volts to 300 uVolts) which I will
> certainly keep.
> Best regards,
> --
> =====================================================================
> Bob Smither, Ph.D.                                  Smither at c-c-i.com
>          Q: What is the square root of 4b^2?
>          A: To be or not to be.
> =====================================================================
>   ------------------------------------------------------------------------
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