[R-390] Mech filter REPAIR Lankford Trial?

[Tim Shoppa]

Dave or Debbie Metz <dmetz at ntelos.net> wrote:
> A question for this esteemed group:  I seem to remember that in the 
> HSN newsletter a few years ago  Dr. Dallas Lankford did a test of 
> using a  current filter available from one of the various electronic 
> suppliers.  As I recall, it wasn't perfect but was 
> relatively  inexpensive. Given the previously noted failures of the 
> existing filters, the options down the road would seem to indicate 
> either a  remanufacture process, or a good substitution.  Has 
> anyone  subsequently tried Dr Lankford's suggestion and could they 
> give us a blow by blow account?  I have to sort of believe we need to 
> explore a reasonable cost substitution for a component that cannot 
> directly be substituted. $600 of filters in a $600--$800 radio seems 
> a bit questionable.

I was just re-reading Dr Lankford's suggestion yesterday. HSN #30,
pages 2-8. He suggests the Collins "low-cost torsion filters", 
6kc BW #526-8636-010, 2.5kc BW #526-8635-010, and 0.5kc BW #526-8634-10,
along with some misc. chokes, impedance transformers from Mouser,
resistors, etc. to match it all into the existing IF deck circuitry
with some mods to the IF deck itself.

But I haven't done it myself. Nor have I even tracked down where to
buy those filters.

What I was really hoping is that someone would give me a blow-by-blow
rundown of how to rebuild the original mechanical filters. That
seems like the ideal solution to me, but maybe it's just plain
unfeasible for someone who isn't already a watchmaker, or maybe
it's just plain impossible even for those who are a watchmaker. (I
could see a good binocular microscope coming in handy with those coils!)

Maybe I'm destined to be the one who gives the blow-by-blow. Clearly
the guys who have wonderful pictures and step-by-steps on PTO rebuild
and RF deck rebuild didn't start out as experts, just mechanically
inclined guys with the guts to give it a try AND (this is just as important)
the skill to write it up.

Tim.