[R-390] Allen Bradley Potentiometer Numbering Schemes anyone?

[Barry]

> Not necessarily a good assumption.  The Allen Bradley Type J was a
> very common part for decades.  They are carbon composition pots,
> available from stock in both linear and "log" taper (actually two
> different linear tapers approximating a log taper).  However, many,
> many custom types were made (reverse log, three-decade log,
> four-decade log, multiple taps, shaft options, etc., etc).  The
> number could well be a Krohn Hite number.
>
> You should be able to determine resistance and curve with an ohmmeter
> (center the wiper, measure the resistance from top to bottom and from
> one of the ends to the tap.  The resistance to the center will tell
> you if it is linear or log, and if log, how many decades and whether
> it is normal (CW) taper or reverse (CCW) taper.  You should be able
> to find resistance curves for the various log tapers easily on the
> web, and they will make evident what you are measuring.  Don't expect
> precision -- it's a composition pot -- pick the closest curve to what
> you measure, and look for one of those.  (If it turns out to be a
> reverse log part, be prepared to look a long, long time.)
>
> Have you contacted Krohn Hite?  They are usually pretty good about
> having parts for older units.  http://www.krohn-hite.com/
>
> Best regards,
>
> Don

I was hoping I could find the specs without having to unsolder anything and 
test it but I suppose that might not be the case.  It's odd, though, that 
Krohn Hite still lists this generator (1200a) as an active unit yet it's 
constructed of discrete components (transistors, etc.) which looks to be 
1980s techniques and components.

Thanks,
Barry