Re: primary taps
Subject: Re: primary taps
Date: Sat, 14 Jun 1997 22:55:56 -0500
From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
> > Hello all,
> > Since I will be taking some time off
> > the next couple weeks I hope to get some
> > serious coiling done.
> > One thing I need to work on is my primary tap.
> > After raising my primary capacitance I noticed
> > that my primary tap gets quite warm.
> > After several extended runs this piece was too hot
> > to touch. So obviously my arrangement of a large
> > alligator clip for a primary tap has some amount
> > of resistive loss. I had attached 1/2 sections of
> > small copper tubing to the jaws to increase the contact area.
> > My question is to those of you with operating coils.
> > What are you using for a primary tap?
> > Just looking for a few ideas to lower the loss in this area.
> > TTYL!
> > Mike Hammer
> > mhammer-at-misslink-dot-net
> As you have noticed, the resistive losses from the primary TAP
> mechanism can be excessive. The losses are from several factors.
> 1) The currents are just obscenely high. But that's what we WANT, so
> we will NOT try to reduce *that* in any way :)
> 2) With extreme high RF currents you need a large surface area to get
> the current transferred. The stupid little teeth on even the best
> 'gator clips are pathetic for RF use. The points just intensify the
> So, get rid of the stinking teeth and increase the surface area.
> Grind the jaw structure so that a maximum surface area come in
> Add a more robust surface area by soldering on copper pieces shaped
> so as to maximize surface contact (not too easy since the shape of
> the spiral changes from turn-to-turn). Easier for you solenoid guys,
> as the pitch and radius are constant in that form of primary.
> Use a MUSHY metallic material to make the contact. Think metallic
> Braid. Think of the outside metallic braid on coax cable. Yeah, I
> know that everyone tells us not to use braid. But they are talking
> about the main power runs, my friend! HERE is a place where the braid
> has a quality that overcomes its defect. The great MUSHINESS of the
> braid makes it ideal to create a larger surface area contact.
> Try *this* with your existing clip lead setup: wrap two or three
> turns of braid **tightly** around the desired tap point. Let the clip
> lead sink its old 'gator teeth into the braid. Not perfect, but a
> definite improvement! (And ridiculously EASY to implement, for all
> you lazy bones coilers out there). How many wraps you can tolerate
> depends on the size of your 'gator, and the spacing between primary
> All right, so now that I have convinced you of the joys of braid,
> consider attaching the braid right to the inside of the jaws of the
> 'gator itself. You can file away the teeth and that will give you
> more room for the braid. Solder it only OUTSIDE the mouth of the
> 'gator clip. We want the stuff between the jaws to remain MUSHY. Be
> careful, as the braid LOVES to wick up solder. TIN the outside of the
> jaws and lightly tin the end of the braid. Heat up the jaw until the
> solder melts and then touch the tinned end of the braid into the
> solder on the jaw . Hold the braid in a needle nose pliers jaw,
> tightly and near the end. This will restrict the solder wicking by
> drawing away the heat. It will also prevent your fingers from having
> the permanent imprint of wire braid branded into them.
> After soldering one end, wrap the braid along the inside of the jaw
> and solder the other end on the other side. What you want is a run of
> mushy flat braid across the inside of the jaw. Do both the top and
> bottom jaws.
> An alternative to going across the width of the jaw is to run it down
> from the top of the nose of the jaw, loop it INSIDE the jaw, and
> around such that it then comes back out across the bottom of the
> bottom jaw. Soldered on the outside, of course.
> There are MANY variations on the theme. Pick one. Make a mushy jawed
> 'gator clip. Amaze yourself. Impress the neighbors.
> 3) With really huge currents the TYPE of conductor becomes very
> important. Heavy duty solid COPPER is best. It is also one of the few
> metals that really solders well. So if you are going to modify a
> 'gator clip, I suggest beginning with a solid copper one if you can
> get one. Trying to solder aluminum 'gator clips is an exercise in
> frustration. Save your energy and your sanity. Buy copper 'gator
> Now, some of you are using those dumb little Radio Shack mini 'gator
> clip leads with all the cool little colored booties on them. Doomed
> to failure from the word go. Not enough surface area to conduct our
> obscene RF currents. These babies get hot enough for the solder to
> melt and the plastic booties begin to drip off. Forsake the wimpy
> mini gator clip and go for the Macho 'gator clip. Think Surface Area.
> 4) 'Gator clips are made from two sections. In a high current RF
> environment this is bad news, as the second section has only a few
> minor points of contact with the main section. This means a high RF
> resistance for half of the clip. This in turn means lots of heating
> WITHIN the 'gator clip itself. Solder coax braid from the wide top to
> the wide bottom. Keep it short and WIDE. Really industrious little
> coilers will find ways to do this work from the INSIDE as well as
> from the outside. Think Skin Effect.
> 5) And the final 'gator clip modification: Throw out the stinking
> gator clip. Build you own Compression Fitting Primary Tap. This is a
> tap that is designed so that it is primarily a PERMANENT TAP, but in
> a Temporary sort of way. A 'gator clip is temporary and makes a lousy
> permanent tap. Soldering and other such methods are permanent and you
> have to live with it.
> A compression fitting can be fabricated in many ingenious ways, but
> its main feature is that you can move it around, but once you are at
> the right place, you can tighten this sucker down and leave it there
> forever if you want. The down side is that it takes a bit longer to
> move it around. But it makes an EXCELLENT connection.
> I have seen small hose clamps used. Properly trimmed they aren't all
> that bad. These work best on larger diameter tubing.
> The compression fitting has SOME means to clamp the metal tightly
> around the primary coil. The metal that gets clamped should have some
> flexibility, but most importantly it should make an extremely tight
> connection with a good sized surface area.
> The material should be something that can take a certain amount of
> flexing without breaking. I have used copper strapping to good
> advantage. You can make your own from sheet copper, or actually buy
> pieces that are about 1/2 to 1" wide at building supply stores. You
> can also use wide flat braid as the flexible conductor part and use
> brass plates to do the compression part.
> The compression part consists of some means to pull the strap tightly
> around the copper tubing and secure it. I often use brass plates that
> I have drilled and tapped so that one plate has holes larger than the
> screws and the other has been tapped so that the screw can be secured
> by that plate. Also connected to this brass plate is the supply lead.
> It may be soldered or also compression clamped. Think surface area.
> Sometimes I attach more than one feed lead per clamp. That increases
> the surface area of the feed lead while keeping it relatively
> I normally have the flexible flat copper/brass or braid section
> soldered to the two afore-mentioned plates. Solder them well, as the
> solder is going to be providing physical strength to the assembly.
> Another method is to use another plate to clamp the flexible metal
> band to the master plate.
> If using braid, consider first rounding the edges of the plates that
> are where the braid passes by. Otherwise the sharp edges will bite
> However you decide to do it, get the spacings adjusted so that when
> the flexible piece is wrapped around the tubing and you tighten down
> the screw(s) the unit is firmly attached with a decent surface area.
> Hope the information is of use to someone.
> Fr. Tom McGahee
Mushy jawed 'Gator' clips using braid. I *love* it! I have a small
coil with a plain old alligator clip on the flying tap that is gonna get
right now! Thanx for such an excellent idea.