[R-390] Mech filter REPAIR

[Flowertime01 at wmconnect.com]

Tim,

The only part I have not done or seen done is to run the old wire
off the bobbin. 


There are at least two different mechanical bails inside that hold the
resonant disk stack. I imagine they have different stuff potting the coil 
windings.

I forget the name of the Fellow at fair who was doing these repairs on a 
bench that would give OSHA fits and never imagined ESD procedures. Not that either 
of those asides are required to do these filter repairs.

After every thing else you have done to R390's, doing a filter repair is just 
another rafter noon on the bench.

Someday there will be many more pictures on the web to view. Someone will 
count the sorry little bits to satify inquiring minds of the hoary details.

The real sticky wicket here is, what is the potting stuff and how do we cut 
it.

The guy at fair had the parts all cleaned up and sort of waved a hand at it 
as if it was a none issue. This may only be true in some models. Or it could be 
a real pain.

My personal best prior to 1975 was just a broken wire and I did not probe the 
potting gunk or the foam mess. I had no need to inquire and I saved a 
receiver from the dead line rack. It was better to just fix it and not ask why. I 
wrote the problem off as a cold solder joint on filter. I did not explain exactly 
where. I put the 4 plus hours off as sorry trouble shooting procedures. Hey 
I'm Polish and stuff happens.

I did spend some time at Fair Radio and swapped war stories as a filter got 
rewound, rewired and resoldered on the bench and tested with a sweep gen and 
scope. The Guy had worked on that process for some time and was happy someone 
wanted to actually see some of his work. If I could remember names I would have 
gone much further in life. Its a curse I have to live with. To find someone 
who could follow the conversation was a God Send for him. The Folks at Fair move 
a lot of stuff but they are mostly logistics minded not hard deep bench 
repair types. Wonderful people at Fair who will help you find any thing ant day. 
They just do not relish the smell of vintage solder like some of us do. 

The number of disk in the stack determine the resonance. Narrow band filters 
have the disk spot welded a bit closer to each other.

Tim commented.
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.

I agree. Someday we will get it all written up and photographed and posted.
Its Amazing how much is yet to be done.

Tim again commented.
 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!)

I have been in there and done some.
It is not watch maker work.
It is hard, It is craft, It is not impossible.
I have watched someone go into it further than I have and come out with a 
working item that after resoldering the sleeve you would never know it was a 
rebuild.


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, you way be it. Take lots of photos, We never have enough photos.
We can rewrite and ghost write any thing if we have the photos.


How do we get this potting mix off the coils? The Guy at Fair Radio was just 
working with an Exacto knife and some solvent to clean up the gunk foam.

Maybe some filters have a potting stuff that cleans out and other models 
have this stuff that we may never be able to work past.

Time to melt some filters open and perform some inspection.

Fellows, How about you lend R390 owners a hand if you have a bad filter.

Pop open what you have setting around broken and tell us what you find.
Model number on the can. band width. The bail style and potting mix.

You may find a loose wire and fix one while you are at it.

Roger L. Ruszkowski   </HTML>