The AM Forum

Whats the best way to attach the smaller "input" coil to the main coil?

Functionally, I know I could just wind the wire right over the copper coil, (especially since at present I'd only be running a dx-60 into it) but I've got a little bit of "vintage" hardware, and I'm making an attempt to have this thing look as old-buzzardly as possible.

Any ideas? Pictures?

Thanks,
Jason kf6pqt

Hello
I'm attaching two pics of my version of the K1JJ TUNA.
I used 40 turns of 1/8 copper tubing for the big coil wrapped on a 4 inch piece of Plastic pipe
And the input coil was 5 turns of # 10 wire on a 3 1/2 inch coil RTV'd inside the big coil.
The input coil connects to your radio and the big coil will have to be tapped out to match the aerial to the radio system. I  had a vacuum variable cap available and that connects across the entire big coil. You can SEARCH for the K1JJ tuner and you will see endless postings.
Fred

One last thought.
It becomes a game to tap the cap and the ladder line to give you a match. Make sure that there are the same number of windings used to keep the RF power balanced OR you  can use an RF ammeter connected to each side of the ladder line to be sure that the same current is flowing on both sides of the ladder line. All tuning is easier with an MFJ analyzer. I got three bands figured out in 1 hour.
Fred

Fred, yours is the only one I've read about who's has the input coil inside the output coil. (and the only one who's posted pictures!) For the sake of function, I gather either way will work, but I seem convinced that I want to put the input coil on the outside.

And yes, I've got the MFJ-o-matic, and several WWII rf ammeters and neon bulbs and such, just haven't yet figured out how I want to arrange that section.

Thanks,
Jason kf6pqt

I know I have seen online that Brent, W1IA has his transmitter coil inside.  I was planning on putting mine on the inside as well, but I have yet to start it, so I have nothing to show you, so here are the pics he posts on his site ( http://home.comcast.net/~w1ia/ (http://home.comcast.net/~w1ia/) ).

(http://home.comcast.net/~w1ia/100_0902.JPG) (http://home.comcast.net/~w1ia/100_0902.JPG)

(http://home.comcast.net/~w1ia/100_0899.JPG) (http://home.comcast.net/~w1ia/100_0899.JPG)

(http://home.comcast.net/~w1ia/100_0900.JPG) (http://home.comcast.net/~w1ia/100_0900.JPG)

Yep,
My primary input coil is inside the secondary as well.

Most pictures and articles you find on the net are the same....
Just goooogle  "link coupled tuner", and you'll find some pics/info....

I'm sure it would work just dandy either way....


Both my coils are made from 1/4" copper tube....
Why?.... cause it was there.......


The ends of the primary come through the secondary (I flattened them so they are thin enough) and I wrapped kapton sheet over them for insulation...



Anyhow.... I believe K1JJ  mentioned plastic wire ties to secure the primary to the secondary......

Black crackle painted base. White ceramic standoffs. Neon bulbs everywhere.

Painted wood, open relay racks.........  klc





  hugh hugh   he said wood

I think that 6T 12-gauge Teflon wire tied (nylon ties) to the copper tubing is fine.  However, 1/4" copper tubing is too light and 1/2" tubing is overkill. Soft 3/8" copper tubing might be just right...

A side note: If you need a vacuum cap to handle the voltage, I'd say you have a mismatch that's WAY too big, and this should raise major safety concerns if stringing a 600 Ohm ladder line in any direction other than straight up! 

I saw a cool way to put taps on a coil when I was at LTI a couple weeks ago. You take a crimp lug say for #4 wire and a 1/4 inch bolt and bend it into an L. Slide the tubing through the crimp section and slide it to the tap area on the coil and solder it in place. The other end of the lug will take a bolt so you can terminate copper strap to the lug.
The solder joint is over a big area so resistance will be low and the lug at the bolt end is nice and wide to take the strap. Silver solder would also help.

No need to attached anything. Just wind both coils together on one form. You can even wind them initially as one conductor and then make cuts in the appropriate places.

I have been burned too many times using the standard transmitting variables. There's always that disappointing arc over just when you thought you had it all figured out.
If the builder can afford (I have had good success with e-Bay) or has a collection of vac variables, go for it.

Fred

Fred,
The nice thing about a bread slicer is you can recover from an arc. A vacuum cap will weld if there is a good flash over making it a good .22 target. I have 1/4 inch spaced cardwells and I can flash them if I run the Q up too high. I would use a vacuum cap in a low z circuit to handle high rf currents but not at the end of open wire line at high Z.

Jason,
I use Plexiglas strips with nicely placed holes for the large coil and smaller holes in the center to wind the teflon wire.  Wind the copper tubing on PVC first.  When drilling the Plexiglas, make sure the holes are a loose fit and then screw the copper coil on both Plexiglas strips at the same time.  Worked great!
Dave / KA2J

Cardwells are very buzzardly. I gotta say, seeing that vac cap in that tuna looks sorta gay.  :-[

More shots of my set up... Dave / KA2J

Dave,

One Saturday morning when you were on the air, your wife was sitting in a chair on the first floor, and she said her feet were getting hot.  QSL?

That's a serious tuna up there!!
I agree, Frank, at the end of a long wire there are a new set of problems. The setup here has been a balanced aerial.
Sorry, DERB that vacuuum variables look gay.
Fred

My tuner is in a 5 foot rack with a pair of 5KW variable inductors and a pair of 300 mmf 1/4 inch spaced Cardwells. RG393 balun. It is ugly and buzzardly with a KW matchbox sitting on top of it for effect.
no gay parts

I'm just trying to keep up with all the uber cool nerdspeak, Phred.

Tom KLR wrote...
One Saturday morning when you were on the air, your wife was sitting in a chair on the first floor, and she said her feet were getting hot.  QSL?

Yes Tom!  It was the first time my radios ever gave my wife a warm feeling!

As far my tuner having a vacuum variable...  it works nicely with my 1954 T-368A which has two stock masculine vacuum variables in the RF deck!  I wonder how old something has to be before it is considered old and buzzardly?

Dave / KA2J

Dave, We were just funin Vacuum caps are very manly.