Hi Gene,
<<<However, as many readers of this probably know, it is, ah, "uncommon"
now.>>>
Heh heh, tell that to all the guys running BC-610s. It sounds like you are
trying to construct a linear amp but with a "retro" design. If you have
not already done it, I'd start looking for old ARRL Handbooks from before
~1952, as they'll have a lot of link coupled tank circuit designs, but
mostly for AM and CW rigs. They can be found at hamfests. What I have seen
had the jack bar link connected to the feedline to the antenna. The guys
running rigs with those tank coils move the link with a long insulated tool,
like a PVC pipe a few feet long with a hook or something on one end to hold
the swing link bar. There's B+ on the coil. I recall one advantage (if
you have to find a silver lining) is that you don't need DC blocking caps.
Yes, as others have said, these tank circuits are notorious for poor
harmonic suppression, so these days you have to run the rig with a feedline
tuner to get an extra 15 dB or so of harmonic attenuation, otherwise you
won't be legal. Of course when you change bands you have to power down the
rig, and use a shorting stick on the coil before removing it. I am mostly
familiar with the B&W low power coils, the TVL series I use in one of my
rigs, but the high power ones were I think designated HDVL (don't hold me to
that) and I bet they'd be okay for legal limit. Actually, if you could get
photos of them to see the dimensions, no. of turns and wire gauge you could
probably construct your own with large banana plugs and jacks. The link
just has to be a coil of the same diameter with a few turns on a
non-conductive arm attached to a friction hinge.
Here's an example of what I mean:
http://www.qsl.net/la5ki/big/bc610co.jpg That's a coil for 40
meters.
Here's a guy who turned one into a link coupled output for 160 m. ( but not
a swing link):
http://www.bunkerofdoom.com/w5frs/PP_808_160M_amp3.JPG
Here's another one that gives you some construction ideas:
http://www.ici-on-vend.com/images/Coil-1738-pour-BC-610.jpg
Note that with the 610 coils, the link varies its inductive coupling by
rotating, not by swinging in and out. I forgot about that, sorry. But you
can still get some idea of coil size and mounting with the banana plugs for
making your own.
73
Rob
K5UJ
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