The composition and manufacturing techniques for carbon brushes is very wide and varied for exact applications. Operation at high altitude is a serious concern because of wear, dust production, and the possibility of causing a communtator flashover. For ground use, these are not much of a concern. The brushes were not pure carbon, there were additives to reduce wear and give stable current transfer at differing temperatures. I have many decades of experience with these, most of it in the elevator craft where electrical stability and long wearing are paramount. Even if you use your equipment a few hours every day, you should not have any problems with re-shaping brushes to fit.

   B.Gentry, KA2IVY

One thing about using dynamotors with your milsurp, they last a very long time on the ground, compared to  operating at up to 30K feet in unpressurised planes where  they arced like the dickens up there.  A contact I have who restores electrically operated turrets for WWII AC like the B17, said he has never replaced the brushes in the amplidynes that power those turret motors.  That also brings up a question as to  their composition.  I wonder if those brushes intended for high altitude, had a different make up than those used in motors that stayed at sea level?  Maybe a harder carbon formula to last over several missions  from England to Germany and back?  Is there any data on how long the brushes did last in the ETO and how often they were changed?  Perhaps they left the radio gear off most of the time, but the intercom system had a dynamotor powered amplifier, BC347,  that had to be running all the time.

Charie, W4MEC in NC

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