[R-390] Smoke got out

[Charles Steinmetz]

dog wrote:

> I'll have to agree with you. I really can't see any other reason. But
> where was the vibration, etc, after 51 years, maybe it was just the 51
> years and time?

Mechanical engineers' Rule 11:  "There Is Always Vibration."  There is 
also always thermal cycling, which rubs surfaces that are in contact 
against each other.  And also, shifting when the radio is moved, lifted, 
flexed, etc.

I expect that, like Norman's radio, yours had the (insulated) choke 
windings touching the chassis right from the factory.  [NB: this is, and 
always has been, an absolute no-no in military electronics construction 
standards.  Collins actually wrote and published the standards back 
then.  Rest assured, the ghost of Art Collins is even today haunting the 
assembler and the inspectors who let that slip by in the next world.]

It takes very little vibration to wear through a thin enamel layer and 
allow direct metal-to-metal (wire-to-chassis) contact.

Best regards,

Charles