[R-390] Re: Line filter issues possibly solved!

[Drew Papanek]

On identifying a defective line filter as the source of his noise problem 
Adam Vaughn wrote:

" Might anyone have a spare line filter lying around that they could spare?"

American Trans-Coil has the filters; you might also try Fair Radio Sales.

The line filter's internal capacitors are paper type; these are just as 
susceptible to leaking/arcing/failing shorted as those Black Beauties used 
elsewhere in the radio. Recapping the filter would be a good idea.

Some have replaced caps inside the filter (reportedly potted in beeswax); 
opening soldered housing requires patience, a torch, and a small hole 
drilled in filter housing through which pressure will vent and scalding 
melted potting will spew.  When replacing those caps, only use types 
specifically rated for line bypass service.  Regular caps will not cope well 
with the sometimes huge transient voltages found on the line.

While you're in there you could change filter configuration to eliminate 
nuisance tingles from the chassis and stop tripping of GFCI's.  Bypass line 
to neutral, then neutral to chassis (grounded).  I'm not sure if that would 
reduce the filtering effectiveness.

You could also fabricate an adaptor plate and replace filter with IEC 
chassis mount filtered connector (available inexpensively from Mouser and 
other sources).   Units rated for lower current carrying ability have larger 
inductors which make the filter more effective.  A standard computer power 
cord is used with these connectors, making for a neat and clean 
installation.   Rumor has it that some recently surplussed R-390A's had this 
setup installed by the Gov't.

For a lively and informative discourse on line filters and related topics, 
goto r-390a.net    .   Click on "References" , "Pearls of Wisdom", "Power 
Supply".  You will find line filters mentioned beginning at about page 40.

Drew

_________________________________________________________________
MSN 8 with e-mail virus protection service: 2 months FREE*  
http://join.msn.com/?page=features/virus