[R-390] Second R-725 on ebay

[Roy Morgan]

On May 9, 2009, at 8:28 AM, ToddRoberts2001 at aol.com wrote:

> ... a true R-725 has a mu-metal shield added around the outside
> of the round PTO shield.... Does anyone know if it really makes a  
> difference

It COULD be that the shield was needed in aircraft installations  
because of the use of 400  cycle power in other nearby equipment.  The  
400 cycle fields might cause more trouble than the same power at 60  
cycles.


> i... are places that sell
> mu-metal foil that
> one could wrap around the PTO can.

Likely, though I don't know about them.. Note: the Mu Metal sheets are  
formed carefully in manufacture, and mis handling the material can  
reduce the shielding quality quite a bit.

Some oscilloscopes resorted to mu metal shields around the CRT.  Low  
acceleration voltages may have made that necessary.  So look for that  
kind of thing in derelict oscopes at hamfests.

Roy

Roy Morgan
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Groton NY, 13073
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