RadioBanter - View Single Post - Lattice-wound RF choke replacement, 50 years later

August 13th 05, 01:50 PM

wrote:
[[Toroidal chokes]]
Problem is, if this is a restoration kind of project similar to
old automobile restoration, toroidal forms won't do...just
weren't many in the old transmitters of the 1950s and before.
Anything of the same construction type is going to be an
expensive special-order thing now. :-(

In fact, this isn't quite a "restoration to original build" type
thing, it's more of a "fix some old stuff that's been sitting on the
shelf for years and put it to use" type thing. Most of these units
are in pretty good shape, and I'm guessing that after the RF chokesdied
they were swapped around at hamfests for a few years with each
owner realizing they didn't have that choke and passing it on to the
next guy... eventually ending up with me.

In fact, Pi-w
ound chokes are still listed in the Hammond catalog and
a couple of them are stocked by AES. I ordered a 2.5mH one which ought
to be able to handle the 100mA or so that a single 6146 will need and
I'll grid-dip it and try it out.

I would still like to find a good reference on lattice-wound and
Pi-wound coil winding in a do-it-yourselfer's workshop. I think
I remember seeing a book that shows how to build a little coil
winding machine that'll do some of the ornate pi winding, and now
I kick myself for not buying it at the time.

Even though the choke fires took out some stuff, the ceramic core
seems to be intact in most cases and I think I could rewind something
useful and authentic-looking on them. (OK, I'd use enameled wire and
not that funky real skinny cloth kind!). Again the intention is to
put these rigs back on the air after fixing whatever is necessary.
Having
powered them up, most of them are fine right up to the final stage (OK,
they generally need new electrolytics in the PS) where everything stops
because of plate current. I probably will replace the tubes in
mostcases and I'm guessing that after I get plate current flowing again
and
replacing the miscellaneous capacitors blown up in the final
compartment they'll
need to be reneutralized.

Tim.