Hello to all the members

There has been considerable discussion on the time-nuts site regarding the HP3458, which I would like to add to my other HP DVM's. This is a problem due to the relative rarity, and therefore cost in the UK. But I have got a 3457 and a 3456 in my lab.
What is the general opinion of the 3457 - is it a good deal short of the 3458 - I gather it is all down to the voltage reference device.
It would seem that obtaining a good DC voltage standard (mine is a Fluke 731B), is much more difficult than the frequency standard, with a heap of GPS and other gear at inexpensive price levels. Any good designs for this purpose, or is it best to find commercial products.
Any advice on these matters would be welcome.
Roy

Danger Signs:

1. The seller states it as "untested" and/or claims not to have even
   bothered to power it up and run self-test.
   ...Note that many such boxes have hardware failures. Your original
   acquisition cost + repair can easily exceed cost of buying a fully
   tested unit.

2. The seller's photo shows it as powered up but you can see "Err" in small
   letters below the main characters in the display.
   ... "Err" means an error was reported and the seller would need
   to hit "Blue Shift" Error to find out which error(s).

Watch out for the Version of its A5 Outguard Controller:

---=====

1. Old version is 03458-66505 (first released in 1988)
   or 03458-66515 if opt. 001

    It has 3 SRAMs, each having a non-replaceable internal battery that
    lasts 10 to 15 years. When the batteries crash, you'll loose your
    cal constants and your DMM won't work. The fix is to either replace
    the 3 SRAMS (expensive) or upgrade to the new ver. A5
   
    The SRAMS are qty 2 DS1230Y and qty 1 DS1220Y.
    Check the datecodes on them.
   
    Bottom line: If date codes are more than 10 years ago,
    you're living on borrowed time!
   
    Firmware might be very old.
   ...depends on age but might be between ver. 2 to ver. 8.
   

2. New version is 03458-66547
   or 03458-66548 if opt. 001

    Much better! Uses new version Non-volatile RAM
    with user replaceable batteries!
   
    Has much newer version firmware.  (Probably ver. 8 or later.)
   

Cheers,
Greg

IMO the 3457A, 3456A and 34401A are all excellent DVMs. All three DVMs must
be adjusted at many cardinal points for DCV, ACV and Ohms. Of course these
adjustments are via physical pots in the 3456A, whereas most are via
electronic cal constants in the 3457A and 34401A.

I would say that the 3457A is a little bit the predecessor of the thinking
that went into the development of the 3458A.

But the 3458A is still king by a thousand miles. Nothing else comes close.
Its internal "ACAL" routines take advantage of the 0.02ppm linearity of its
DAC, establishing ratios from one range to the next (and from its LTZ1000A
zener reference voltage to full-scale on its 10V range). Consequently its
adjustments to the external world require only a short, a 10Vdc standard and
a 10k ohm resistor. It even adjusts its own AC freq. response (during ACAL
AC) by adjusting for the most pure flat top of an internally generated
square wave. Its most accurate AC mode (AC SYNC) digitizes AC sinewaves and
then calculates and displays their voltage.

After a 3458A has been adjusted at "0", 10Vdc and 10k ohms (and SCAL AC if
needed for AC HF frequency response above 2MHz) - and after internal ACAL -
it will meet all published specs. (Or else it's broke and needs repair
because there's nothing else to adjust.) It's had an amazing long life (21
years) so far.

Cheers,
Greg