[HBR] HBR-14 coil info

[Bill Fizette]

Very helpful, Walt!  Thanks very much.  (And thank you for all the other 
postings on your various HBR adventures...they are all read here and saved.)

73,  Bill  w2dgb


----- Original Message ----- 
From: "Walt Hutchens" <waltah at earthlink.net>
To: "HBR Receiver List" <hbr at mailman.qth.net>
Sent: Monday, January 30, 2012 8:16 PM
Subject: Re: [HBR] HBR-14 coil info


> An alternative to Breck's excellent info on using PVC pipe sink tail 
> pieces
> to make HBR coil forms is to use 1" Schedule 20 PVC water pipe.
>
> The 1" is the nominal inside diameter:  It's actually larger than that and
> the outside is very close to 1-1/4".    Because the pipe fittings go on 
> the
> outside, that's the controlled dimension and will be the same for all
> strengths, etc.   So this material lets you wind coils using the W6TC 
> specs.
>
> I recommend the schedule 20 pipe because it's plenty sturdy enough 
> (thicker
> wall than the sink tail pipe pieces) and will fit snugly over the plastic
> base of a junked metal octal tube.   You take off the metal part, save the
> Bakelite plug, clean it up and it's a force fit in this PVC pipe.
>
> A 10' length of pipe will cost under $10 and will make more coil forms 
> than
> you can ever use: Use a radial arm saw or a miter box to slice off 3"
> pieces.
>
> Also slice 1/4" sections off each end of some 1" couplings: These can be
> slid or shoved onto the top end of each coil form for reinforcement and to
> act as a grip for pulling the coil.
>
> The inside diameter of the couplings is tapered so the first slice will be 
> a
> light push fit and the third will be a tough fit.  But if you chamfer the
> respective corners and have a block and hammer at hand to give it a whack,
> you can always get the rings to go on.
>
> I glue the top rings on with PVC cement before starting on the coil.  For
> the HR-10 to HBR project I have experimented with leaving out the APC
> trimmers on the antenna and mixer coils.   This works fine: You don't need
> anything like the precise tracking required for the oscillator coils. 
> You
> just have to select the right fixed capacitor and adjust the tap location
> and turns spacing slightly to get the coil to track.
>
> For the forms that need an APC I use a Dremel tool with a rotary file bit 
> to
> cut away inside the top until the APC I'm going to use is a snug fit. 
> Then
> I drill the necessary holes in the form, wash, dry, and wind the coils,
> bringing the leads out the bottom.
>
> I solder on the APC leads and any required fixed shunt cap, then push it 
> in
> place.  All the leads coming out the bottom of the form are now stripped,
> passed through the respective pins in the plug, and clipped with about 
> 1/8"
> sticking out the end of the pin.   The coil can now be carefully pushed 
> into
> the appropriate socket and tested.
>
> You'll have very little trouble with poor contact between the loose leads
> and the inside of the pins ... just once in a while.  If it's suddenly 
> dead,
> poke or twist the coil slightly.  However don't set the coil aside for a
> couple of months and expect it to still work well in loose lead
> configuration -- there'll be just enough corrosion to make things
> squirrelly.
>
> You can do everything except oscillator stability testing this way and you
> can get a rough guess about that.
>
> Note that everything is just pushed together: Even the most dramatic
> adjustments can be made without starting over, by carefully prying the 
> coil
> out -- you can't pull it because the plug isn't glued in the form -- and
> disassembling.
>
> Of course if you are following W6TC you shouldn't need any redo, but when
> using a different tuning cap, dial, oscillator circuit and tube (and 
> pretty
> much everything else, as I am) there is necessarily some cut-and-try!
>
> When everything is okay you take the coil off the base and push out the 
> APC.
> Glue it in with PVC cement.  Put JB Weld on the base and inside the bottom
> of the form, put the leads through the right holes, push it together, 
> clean
> the outside carefully and test again before the JB Weld sets.   If all is
> satisfactory I leave the coil in the set for 24 hours or so, then pull it
> out, solder the pins, and trim the excess wire length from each.
>
> Clear nail polish laid on in four strips is excellent for locking turns in
> place.   The oscillator will however drift after you do this for up to
> several days so don't try serious stability testing right away.
>
> In the worst case -- a coil requiring a major redo AFTER being glued --  
> you
> can use a fine hacksaw to cut all the way around about 3/8" from each end
> (use great care next to that APC!), take off the top and bottom pieces 
> with
> the plug and APC respectively, make an axial cut in each of the PVC rings,
> and pry it off.   The APC can be cleaned up and reused; the wire can be
> salvaged from the main part for use on a higher band.    You've wasted a 
> few
> cents worth of PVC pipe and a few hours of your time ...
>
> The result looks as good as a commercial form or coil and it's a lot more
> durable and easier to work with than the polystyrene forms.   Among other
> things if you touch it with a soldering iron you get a mark, not a hole.
> And of course you can heat the pins in the Bakelite tube base as much as 
> you
> want without them flopping over.
>
> I'm still doing 40M coils ... few other things got in the way!
>
> Walt
> KJ4KV
>
>
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