17 Dec
2008
17 Dec
'08
11:13 a.m.
On 17 Dec 2008 at 18:48, Tony Duell wrote:
It was quite common at one time. The ones I've
memtioned have ther
traditional H-shaped glass things in them (the Blackburn vavled one has a
pair of them, just bare glass, on a bracket, the Solartron ones have them
encased in a little plastic housing). I have a later DVM which has an
enacpsulated thing with 2 wires comiong out that appears to be a standard
cell, certainly the voltage between said wires, measured on a
high-impedance votlmeter, is about right.
One of the "round-tuit" jobs when I was an instrumentation tech was
replacing all of those Weston-cell-plus-dry cell-plus-calibration-
slidewire setups with Honeywell constand-voltage supplies, even in
L&N equipment. You'd strip out the entire reference-voltage section
and drill and tap a couple of holes in the instrument frame and mount
the supply and connect up the wires (including AC). Took about 45
minutes to do right and you never had to replace another battery in
that instrument. I must have done 100 of those conversions.
One of the things that would probably tickle Tony's sense of
"vintage" was that transistorized chopper amplifiers were just coming
on the scene. Reliability of the solid-state gear was so low that we
asked the manufacturer (L&N, I think) if we could get the amplifiers
in the nice reliable tube version. (We couldn't, but they kept
sending us "improved" versions of the solid-state stuff). I think
one thing that militated against the solid-state versions was
temperature extremes, even in air-conditioned pulpits. The radiant
energy coming from an orange-hot steel ingot was awesome. When the
ingot was only 20 or 30 feet from the instrument panel, air-
conditioning and glass didn't make much of a difference.
Cheers,
Chuck