[Test-Equipment] HP-403 Pegging meters

[Richard Knoppow]

At 04:52 AM 3/11/2008, you wrote:
>I had one that did the same thing and, as I remember, there were other
>HP meters that also pegged, 410 comes to mind.  Don't see any reason to
>fix what aint broke.
>
>I think it was Richard Knoppow that said the meters are easily capable
>of taking the load, and having used HP gear for 40+ years, I never saw
>an HP meter that had a problem either.
>
>Mike
      That was someone else. I think what they stated is that good 
conventional meter movements would take a 1000% overload without 
damage. I don't know this myself but think it may be true but it 
would depend on the type of meter. I can say that the movements used 
in -hp- instruments were pretty rugged. I think by the time the 403 
was made -hp- had switched to taught band movements. Taught band 
support has the advantage of having no mechanical hysterisis. These 
meters also had individually calibrated scales so scale tracking is 
excellent. For instance, the difference between the 400D and 400H 
meters was originally that the H had a better meter. However, after 
the taught band meters were introduced the two had the same scale 
accuracy the only difference being the H had a mirror scale.
      The advantage of the 403 was its battery supply. The meter was 
portable but also completely isolated from the power line, sometimes 
an important attribute.
      In general most of the older -hp- instruments were pretty 
trouble free but there are some caveats. For instance, the 400D and H 
series had at least three different power supplies and a very major 
change in the amplifier design. The earlier meters simply won't meet 
specs. One important change was in the design of the voltage divider 
string. There are two service notes about this on the -hp- archive site.
       All this was some forty years ago so I don't remember all the details.