[ARC5] BC-453 B dynamotor hum

[Kenneth G. Gordon]

On 3 Nov 2015 at 11:10, Chris Bowne wrote:

> I also suspect a stuck or badly worn commutator brush.  On accession I have had
> the CW signal if my command set transmitter setup go from a normal clean note to
> one with a buzz saw character.  A sharp "mechanical agitation" (thump) to the
> dynamotor on the BC-456 modulator cleans things up.  Carbon/copper dust buildup
> in the gap between the brushes and their holder causes binding and resultant
> poor contact between the brushes and commutator.  Do you have another dyno to
> swap in to see if the problem follows the dyno?

For badly worn armatures, I have a document somewhere in the military 
collection here which advises turning the armature in a lathe, then 
"undercutting" the insulators which are between the segments of the 
armature. This requires a saw with a very narrow blade, and some careful 
manual manipulation.

Also, that same document suggests that the brush-holders can become too 
tight for any number or reasons. Testing this requires you to check each 
brush for very easy movement into and out of the brush-holder. If there is 
even the slightest hang-up, you must either slim-down the brush, or widen 
the holder.

Ken W7EKB