On 2012-02-21, Michael A. Terrell wrote:

"DoN. Nichols" wrote:

On 2012-02-20, Michael A. Terrell wrote:

"DoN. Nichols" wrote:

On 2012-02-19, Michael A. Terrell wrote:

"DoN. Nichols" wrote:

[ ... ]

Non-Linear System's digital voltmeters used a series of stepper motors
to implement a Kelvi-Varley divider. Four digits, IIRC. Really noisy
with the sound-deadening cover off for test or repair. :-)

[ ... ]

Which would be easy with a CNC machine. Can you imagine the problems
NCR had making their mechanical cash registers without CNC?

Indeed -- lots of custom fixturing. Actually, I think that the
frame for all the Plexiglas (or Lucite) panels was likely made with a
horizontal mill with a stack of cutters on it cutting all the guide
slots in the sides in a single pass, then assembled to make the overall
frame.


Their early models were brass & steel parts, wih a small glass window
over the mechanical displays.

Hmm ... early being when? I first saw them back in 1960/1961
IIRC.

Speaking of "mechanical displays", we had one DVM at a later
date which was a servo driven Veeder-root counter which rotated the
digit drums do display the position of a 10-turn pot. I forget who made
those. Not very impressive, really. :-)



LED replacements have been available for over 20 years, but they are
even more expensive than the lamps they replace.

Not when you count the cost of replacing them frequently, or
having a crucial indicator lamp burn out in the cockpit. (Of
course, they typically had two or three lamps per indicator, so you get
some warning when one lamp burns out.


They were $17 each, and the lamps were 85 cents. The problem is that
a lot of them were used on AC, and the early LED replacements not only
had to be DC, but the sockets had to be wired for the correct polarity.

Yes -- a problem. That's why I wanted one with a built in
bridge rectifier. Are those made now?

O.K. A quick search finds this:

http://www.martekled.com/-strse-173/midget-flange-based-LED/Detail.bok

and they offer your choice of AC, positive center contact, and negative
center contact. (And, your choice of colors, too.) And the price is
down to $4.25 if you buy in sufficient quantities (1000). :-) Unit price
is $8.95 ea, which is better than it once was, at least.

Enjoy,
DoN.

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