Self-destructing B&W 20 meter coil

[w1vtp]

This coil is self-destructing.  The plastic bars shrink and implode the coil.  Any ideas on a repair.  Also, check your old heavy iron xmtrs tank to see if you have the same problem

Al

[Tom WA3KLR]

Those coils may be 60 years old or older.   The BC-610 versions my father had in his 1946 rig had to be refurbished for the same reason.  As I recall, he stripped off the old "clear" plastic strips and used strips of Fiberglas perfboard, epoxied the strips on to the coil forms (I think).

I was just telling someone at our monthly club meeting last week how I remember seeing nice new BC-610 coils  in my dad's attic space adjoining the ham shack when I was little, and 10 years ago the forms were rotting.  Really made me feel old!

[KB2WIG]

If left alone long enough, the plastic will curl up and the ceramic will crack.  And yes, it will make you feel old.


klc

[N2DTS]

They are not easy to make, I made a push pull triode rig last year, I had built one in the past that worked wonderfully, but I did not have the plug in coils this time so I tried making them.
Total failure, the balance was all out of wack and it was impossible to neutralize.
I scraped it.

I wonder how they did it in the old days, before pre made plug in coils...

[WQ9E]

Al,

I have repaired a couple of mine by cutting and removing the original plastic and replacing with perforated circuit board like that sold by Radio Shack:  http://www.radioshack.com/pre-punched-ic-spacing-perfboard/2761396.html#start=8  Most standard epoxy formulations should be fine around RF, I used some clear 2 part that I picked up at Farm and Fleet years ago.  I also had to do this repair to the coils in my B&W LPA-1 amp which have the disintegrating style turns support/spacers.

Cut the board into strips with shears, I use an old paper cutter.  B&W used two styles of plastic strips and one style just disintegrates with age and at least doesn't damage the coils.

[W3GMS]

If you can locate some Lucite or Lexan stock material drill holes in it at the spacing of the wire.  Use a small center punch followed by drilling a small hole and lastly the correct hole size based on the wire diameter.  What you will end up with is as many drilled hoes as you have turns.  Then with a band-saw cut the length of the material at the center of each hole.  Then you will have two pieces with semi-circles in them.  Put one piece over the turns and the other piece below the turns.  You can use acetone to glue each section together. You will end up what looks like a solid piece holding the turns.

Joe, GMS     

[VE3AJM]

Lots of information about this found in the archives on this site, especially explaining why the plastic cracks and various ways to deal with it or rebuilding the coils.

Just one here:

http://amfone.net/Amforum/index.php?topic=9518.0

Al VE3AJM

[W3NE]

"Self-destructing" is the name for it alright. For several years B&W used strips of acetate plastic under the wire while the coil was wound on a split form that could be taken apart to free the coil when finished.The form had shallow slots to hold the acetate strips in position. Just enough current was passed through the wire during winding to heat it and melt the acetate slightly to keep the turns in place. Jack Williamson (W3GC, ex 3GC) told me that after winding, the wires were further locked in place with a bead of off-the-shelf Duco Cement of all things! In time the acetate strips (same material as in early non-safety motion picture film known for its violent spontaneous self-destruction) and the acetate cement gradually absorbed water vapor that caused their deterioration.

When Jack and partner Barry Barker (W3BGR) went into business, their coils were made in a dingy abandoned textile mill that had been in the Barker family. Jack used to peddle their coils in visits to ham radio stores until business grew and they were able to move to a real factory and continually introduce new and improved products.

We are fortunate there were those two pioneer hams with the ambition to start a business with an unknown future right in the middle of the Depression.

Bob - NE

[fg5fc]

Hello w1vtp
Maybe it's possible to built some stuff like that!

[KL7OF]

Two coils from my shack......The first is a NOS E.F. Johnson HDVL 20 meter coil...The newspaper it was packed in says "1947"  The plastic spacers are in good shape with no signs of deterioration..Johnson obviously used a different material than B&W...
  The second is a coil that I made for 15 meters...#10 ga. solid THHN copper with insulation still on and no spacers...Both coils see duty in my PP 100th rig..

[W3GMS]

Two coils from my shack......The first is a NOS E.F. Johnson HDVL 20 meter coil...The newspaper it was packed in says "1947"  The plastic spacers are in good shape with no signs of deterioration..Johnson obviously used a different material than B&W...
  The second is a coil that I made for 15 meters...#10 ga. solid THHN copper with insulation still on and no spacers...Both coils see duty in my PP 100th rig..

I like the newspaper from 1947!

Joe, GMS

[W2PFY]

If Your looking to repair or patch old coils, here's the dope on that!

GC ELECTRONICS 10-3702 Q-DOPE POLYSTYRENE BOTTLE 2FL OZ

You can find it on epay or on the web. It it the original dope they used way back then.

Some of you might think, that CRAP only last sixty years then it cracks. Let me known when you use it and well set the timmer

Remember when people were giving you the dope on everything? Got some?

[w1vtp]

Joe

I found the tear between the couple a bit eerie.

All: got this reply from my friend Bill, K1BF:

"Hi Al,

Take the coil off the jackbar . Hook it up to a 12v/20a xfmr on a variac. heat the coil until the old plastic can be removed. It leaves a bit of a residue but provides a guide for the new plexi or acrillic bars. Goop is better than super glue for reassembly.

Bill"

[KL7OF]

Joe

I found the tear between the couple a bit eerie.

I wonder if that marriage stayed intact.....The grooms name was MAUL....

[W3GMS]

Joe

I found the tear between the couple a bit eerie.

I wonder if that marriage stayed intact.....The grooms name was MAUL....

Plus, being a Ham Radio operator does not add to the probability of a long marriage, but that is an entirely different subject!  Its all about finding the right one!

A lot of great idea's on how to repair the old B&W coil forms.  Jack Williamson would be amazed that people are still using them.

Thanks Bob-W3NE for your comments.  Bob also knew Jack very well. 

Joe - W3GMS   

[W3RSW]

I too found the newspaper more interesting than ol' scrunched up coils.

 I mean, how much neater can you get than "Joyce Joan La Lone marries a Maul," Tuesday after Aug. 31, 1947.