My return to Classic Cmp - San Diego, software archive, etc.

[Chuck Guzis]

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