B&W and the swinging link

[KB2WIG]

 I am searching for information on the application/ adjustment of Barker and Williamson transmitting coils, Type TVL. These things are plug in coils with a pick up coil that is mounted on an 'arm' and swings....I cant seem to find a 'old' B&W cat a log.'  Googgaling returns very little data, other than some strange porno info..   klc

[N8LGU]

    Wish I had a set for 80 and 40. I am building an 813 maul and plan on using link coupling. Guess I'll roll my own.

[KL7OF]

I don't know the wattage rating on TVL coils.  The B&W HDV coils are used in kilowatt rated rigs and they are 10 or 12 ga copper and the link seems to be plated hard copper.  The link is used as the loading control .  The B&W HDV and the Johnson HDV coils are interchangable and I'm not sure, but I think Bud made some HDV coils as well...Here are pictures of two HDV setups.  First is a PP 100th rig with a 20 meter Johnson coil with the link about halfway in.  The second is a PP 250th rig with a 75 meter coil and the link is at full coupling and is wrapped with friction tape and shellac.

[KB2WIG]

Thanks all..

The  TYPE BVL are  150 Watt input, the TVL are 500 Watt input and the HDVL are 1000 Watt. I have a copy of a Terminal Radio Corp. add from the ??50's. Thats all the information I have. 

Mine (TVL) are cracked/seperated on the ceramic bar. Super glue or cut some plexie glass straps and refabricate ?     klc

[KL7OF]

Hot Glue

[Dave KA2J]

Steve,
How did you get the hot glue so neatly on your coil?  I contemplated using a hot glue stick cut to the correct lenght and heating up the whole strip or the coil and pressing it on.  It would then look nice and neat.  Your picture appears that you may have done something like that.  I ended up using plexiglass.
Dave / KA2J

[KB2WIG]

Steve,
 You mean to use hot glue to glue the ceramic together? Hmmmm..  I wonder if I drill lengthwise and somehow put pins in then hot    glue?? Or epoxy?    A few of the plastik forms are warped, so I think I'll use some plexi on these.

I'm still a little shakey on how these 'links' are actually adjusted.. Seems a little harry sticking your hand in there moving them in and out untill satisfaction. And just sticking coils in the slots and and pivoting the arm in doesn't seem to be any advantage at all....    klc

[KA8WTK]

Some of the old rig designs had the coil and link at right angles to the front panel. Then a shaft, with insulator/isolator connection could be run through the front and adjusted by a knob. The shaft would connect to the link holder at the bottom where it pivots. On my 813 rig (coil parallel to front panel) I extended the link holder with plexiglass and used a push/pull setup (similar to a choke cable) made from the stuff they use in radio controlled airplanes (plastic). All I needed to do to adjust the link, and thus the loading, was push or pull the cable that moved the link in or out.

I have had sucess with hot glue repairing and making new coils that I did not have. For the repair I would cut a strip of plexiglass to fit inside the coil and, while holding it in place, would run a bead of hot glue from the outside down the coil. Worked OK fine. When making a new coil from coil stock or from hand wound coils, the hot glue makes a good way to repair a ceramic jack bar and hold things where you want them.

[W3SLK]

KC said:

Thanks all..

The  TYPE BVL are  150 Watt input, the TVL are 500 Watt input and the HDVL are 1000 Watt. I have a copy of a Terminal Radio Corp. add from the ??50's. Thats all the information I have. 

Mine (TVL) are cracked/seperated on the ceramic bar. Super glue or cut some plexie glass straps and refabricate ?

Here's my nickel's worth of free advice. One way that I rebuillt a B&W 850-A coil set was I took an acrylic similar to Plexiglas®, and melted it in a jar of acetone and then applied the melted acylic with a brush. It worked OK but because of the boiling point of acetone, (read as 'rate of evaporation'), it left small bubbles in the acrylic but worked well. The second thing you could try is to clamp two pieces of acrylic or Plexiglass® so that the coil is sandwiched in between them. Then attach a battery eliminator with current limiting to the coil. This would heat the coil to the point of melting and forming the acrylic around the turns of the coil and the current limiting would prevent you from overheating. I hope this helps.
Of course, your milage may vary. Offer not available in Utah......

[KB2WIG]

acetone & plexie  ---  Poor Mans Q Dope???    .... ..     klc

[KL7OF]

I use super glue or model airplane cement on the ceramic stuff and Hot glue for the coils.....Factory coils with broken or cracked acrylic spacers are easily repaired with hot glue....For homebrew coils,  use two thin strips of acrylic with hot glue in the middle to make a sandwich that holds the coils at the correct spacing.  I haven't tried it but I think an acrylic strip sandwich could be made using acetone or MEK to soften and bond the strips together...  The pictures I posted are of factory made johnson coils...My homebrew ones look OK but they don't look as nice as the Johnsons.....Good Luck...Steve

[Dave KA2J]

Great ideas.  Thanks guys.

[KB2WIG]

Thanks all...   If this works, I'll  have (2) 810s pounding  #$@**&$%## out of  (2) 813  PP

                        PW no more!                  klc

[Roy K8VWX]

         I have used the 5 minute epoxy glue ( the one in two seperate tubes ) - just let it set up a short time and use a flat bladed screw driver to dribble it across the turns. Keep turning the coil until the glue starts to set .With a little timeing and practice you can do a neat job. Have never had any RF problems with the epoxy.

[The Slab Bacon]

Kevin,
         I have been repairing them for years with thin strips od 1/4" lexan and 5 min epoxxxxie. Slice the plexi into 1/4" x about 1/8"-3/16" strips on a table saw. Gently peel off the old spacer strips and glue the plexi into place. (do 1 strip at a time to preserve the original spacing) I have done dozens of plug in coils and even a few of the big 850 tapped pi coils. You will get a little stressed out on the first one or two untill you perfect the technique, but it isnt real difficult.

If you have never tuned up a link coupled transmitter its easy! Swing the link all of the way out and adjust the tunung cap for your dip at resonance. then start shoving the link into the main coil until you get the desired plate current at load. Recheck and adjust the dip (if necessary) and your good to go.
Just think of the swinging link as the "load" knob on a pi tank.

Mikey,
         Melting the acrylic in acetone!! That is pretty slick! I am definately gonna try that one that is pretty kool!! However I like to remove the old spacers if at all possiroo. that was some wierd celulose based plastic (on the real old ones) and it would absorb moisture. (How many have you seen wuth mildew on the plastic) This can definately cause tuning instabilities.

                                                                                 The Slab Bacon 

[W3SLK]

Frank said:

Mikey,
         Melting the acrylic in acetone!! That is pretty slick! I am definately gonna try that one that is pretty kool!! However I like to remove the old spacers if at all possiroo. that was some wierd celulose based plastic (on the real old ones) and it would absorb moisture. (How many have you seen wuth mildew on the plastic) This can definately cause tuning instabilities.

If things go as planned, I will bring down the B&W 850-A that I rebuilt when I stop by after the Timonium fest. Other than the 'micro-bubbles' and it being my first attempt, it didn't turn out too bad.

[k4kyv]

I have been building transmitters using variable link coupling since 1962.

The old plastic material on B&W coils is cellulose actetate, about the same substance as celluloid (with similar tendency to deteriorate with age).  It is thermo-set, not thermo-plastic.  You may notice that you can burn it, but it won't melt when heated.

Other brands may use Polystyrene (Victron), which is thermoplastic, and can be melted with heat.

Over time, cellulose acetate tends to self-destruct.  First, it shrinks, and finally, turns opaque and degrades into a brownish powder.  That's why most of the coils you see nowadays are distorted out of shape.  It also reacts with the copper in the coil, leaving a greenish contamination of the plastic and obvious corrosion on the wire.  Sometimes the shrinkage is severe enough to actually cause the porcelain bar on the coil to break.  The degraded plastic tends to heat up with rf.  I have seen coils that had been in use for years, suddenly burst into flames as rf heated up the plastic supports one time too many!

I usually repair mine with 2-ton crystal clear expoxy.  Epoxy is supposedly a good dielectric.  Plexiglas (acrylic) is a mediocre rf dielectric, but it is good enough for the plastic support strips in air wound coils.  For repair work, I usually dig away all the deteriorated plastic and then run a bead of epoxy along where the original plastic was.  Then after it sets I run a generous second coat over the repaired plastic.  If the wire turns are displaced, carefully re-space them, then temporarily tape them in place.  I find fibreglas/plastic filament tape sold for wrapping packages ideal for this.  I have also used it as a temporary repair when the plastic on the only coil I had fell apart just as I was about to use it.

I have also made repairs using strips of plexiglas glued with plexiglas cement, and I have seccessfully used epoxy to glue the plexiglas, but it doesn't bond quite as well.  Plain old model airplane cement works, too.

I have found epoxy to be the best glue for broken ceramic jack/plug bars.  For that purpose, I wouldn't even think of using hot glue.  Chewing gum would work about as well.  I had never thought of using hot glue  for holding the coil turns, but you wouldn't want the coil to get too hot.  I have seen some of these coils get hot to the touch while in use.

If you wish to make your own, I  recall some construction projects in the 1943 ARRL handbook gives the coil specs, both the commercial B&W type number, and wire size/spacing/number of turns/diameter specifications.  Other issues, give or take a few years, have the same data.  Those coils first became available in the late 30's, about 1937-38. 

Amazingly, no-one had thought of adjusting transmitter loading by swinging the link until the mid to late 30's.  Link coupling was well known, and so was "vari-coupling" where the spacing between two resonant coils was varied, but hams struggled with JS methods of varying the loading of the final that used link coupling until B&W first came out with the "swinging link" coils.  An alternative method is the "variometer" where the link coil is rotated inside the main coil, as in some broadcast transmitters and the BC-610 coils, as opposed to swung in and out of the main coil.

I have made coils from scratch by winding the coil on an appropriate size round glass jar, first wrapped with wax paper.  The plastic strips are glued into place and the glue is allowed to harden.  Then, using a small hammer, the glass jar is broken, and the glass falls away.  The wax paper is to keep the glue from bonding to the glass.  I have never seen a glue  that would stick to wax paper.  Then a second plastic strip is glued parallel to the first one, on the inside of the coil.  I have made some near-perfect replicas of the HDVL series coils that way, but the difficulty today is finding the appropriate size round glass jars or bottles, since most stuff at the supermarket now comes in plastic jars.

I recall an article in QST a few years ago, describing fabricating air-wound coils using liquid epoxy and a mould to hold the epoxy in the proper form until it set.  I don't remember the details, but the form was made with some material that epoxy wouldn't adhere to.  Back in the early 70's I worked briefly at a factory where epoxy moulds were coated with a teflon liquid - actually teflon powder suspended in a liquid.  You painted it on with a small artists brush, and it would dry leaving a milky film.  Then the mould would be filled with epoxy, but after the epoxy dried, the mould was lifted away, leaving the cast-epoxy piece.  The final product was the printer head for impact type dot-matrix printers.  The teflon liquid may still be available somewhere.

[The Slab Bacon]

Frank said:

Mikey,
         Melting the acrylic in acetone!! That is pretty slick! I am definately gonna try that one that is pretty kool!! However I like to remove the old spacers if at all possiroo. that was some wierd celulose based plastic (on the real old ones) and it would absorb moisture. (How many have you seen wuth mildew on the plastic) This can definately cause tuning instabilities.

If things go as planned, I will bring down the B&W 850-A that I rebuilt when I stop by after the Timonium fest. Other than the 'micro-bubbles' and it being my first attempt, it didn't turn out too bad.

Kool Beanz!! I'll look forward to seeing it. I an prolly gonna post the notice announcing the Pharty sometime this week! So far all looks good!
                             
                                                                          the Slab Bacon

[Steve W8TOW]

Lots of good ideas, as with Frank and Don I've been building and rebuilding these coils for years....
only one tx in the shack is NOT using link coupled plug in coils!
I just started turning out some experimental NEW coils on my lathe.
But in the meatiime 5 min 2 part epoxy works FB on repairs.
TVL are 500 watters
BC610 coils are good for about 700 watts or so...
BVL are 150 watters.
M series and J series are interchangable in most circuits.
For coupling PA tank to 50 ohms, 160 m use 10-12 turn swinging link w/ 1000 pF in series to ground off the link. Solder the "hot" center condx of coax to the link, shield to chasis...cap to link and gnd.

for 80 m   470 pF of C and 8-10 turn link
40 m      270 pF & 6 turn link etc...
This is for PP, I never build single ended stuff, but similar combinations should work..

I use an assortment of small "C-clams" to hold the coils to the base while waiting for the
epoxy to dry....Corona dope is still available and I put that on the MEL 160m & 80m coils...as needed.
but sometimes on the 10-14 turn links too...

For old coils, re solder and CLEAN all banana pins & bases, remove ALL old solder.
use DOXIT on the JACKBARS....with a Q-tip...make it shine....


Try low B+ first....watch for flashovers....



gl es 73 steve
8tow

[KB2WIG]

FLASH         The 1941 ARRRL handboo is on line at   



http://www.pmillett.com/technical_books_online.htm

Page 522 has specks on the swining links    klc