Re: Cleaning variac surfaces?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ray von Postel by way of Terry Fritz <teslalist-at-qwest-dot-net>" <vonpostel-at-comcast-dot-net>

Terry:
I assume when you say "Variac®" you are talking about those made by General 
Radio Co.  If so, from GR Cat. N: " All V-model Variacs® have brush tracks 
treated by the Duratrack process, which puts a coating of silver alloy on 
the brush track surface. This is the most important advance in 
autotransformer manufacturer since the original variable autotransformer 
was developed by General Radio in 1933."  If your Variac®s are of the "V" 
model such as V-20 or V-50 then what you are seeing may be tarnished silver 
alloy. The movement of the brush will take care of that.  The finest 
available sand paper will clean other contact surfaces, but never use any 
thing with an emery, silicon cabide, or rouge type abrasive to clean 
commentators or autotransformer tracks. These are to one degree or another 
conductors and are known to sometimes cause shorts.  Sandpaper does not 
have that bad habit since the abrasive is essentially glass.

Ray



>Tesla list wrote:
>
>>Original poster: "Terry Fritz" 
>><mailto:teslalist-at-qwest-dot-net><teslalist-at-qwest-dot-net>
>>
>>Hi All,
>>
>>I have a few never used but older varaics with some tarnish on the bare 
>>wire winding surfaces that the brush rides on.