[sdiy] 1/8" shaft pot comparison: Honeywell/Clarostat vs. Vishay & Bourns

[Robin Whittle]

Thomas White's recent message about Vishay (who took over Spectrol)
pots prompted me to write this comparison.

What used to be "Spectrol" pots are now made by Vishay, and I think
the white Vishay 148 (conductive plastic) (and I guess the 149
cermet) pots are horrible.

They in no way resemble a Spectrol 148 (black plastic, made in
Mexico) pot which I recently bought from Farnell.  That would be old
stock - and my impression of it is very positive.  The old Spectrol
148 has a nice feel and is not to stiff.

The Vishay 148s I got are bad in these respects:

  1 - Very stiff, with a rough kind of stiffness and considerable
      stiction.

  2 - Have (I guess) a few degrees of slop between the shaft and the
      wiper actually moving.

  3 - A bump in the friction at each end of the travel, due to the
      wiper riding up on the raised surface of the conductive
      material where it overlays the metal contact layer.

Also, internally, there is just a metal-to-metal pressure contact
between the pins and the resistance element - not a rivet, solder or
conductive epoxy.


Vishay 248 pots are not available in log AFAIK.


Vishay P9 pots are smaller and I recall they are too stiff - mine is
pulled apart now.


I bought some Bourns 51/53.  I thought they were OK, but too stiff.


I am very happy with the Honeywell 308 series, such as the 308N10K
from Digikey.  These are fresh production (0826 date code on the box
and 0710 on the pots) from Mexico and arrive in a Clarostat box.

They are light and very smooth, apart from a barely perceptible bump
at each end.  These pots are begging to be tweaked!

Internally I think they are very well constructed, with proper
joints, no slop, grease throughout the wiper area as well as the
rest of the pot.


BI Technologies have recently gone into production with 1/8" shaft
conductive plastic pots: P260/261.

This is most promising, since I was concerned these would be hard to
get in the future.

  http://www.bitechnologies.com/pdfs/p260.pdf

I asked for some samples via their web form, but nothing happened.

BI Technologies claim a lifetime of a million cycles, while the pots
mentioned above generally have a spec of 50,000 cycles.  This
doesn't mean the pot would stop working after 50k cycles - just that
its resistance behavior might not meet the original specifications.

 - Robin