Scott,
You can rewind that choke pretty easy using 28 gage magnet wire. Just fill the
form up the length of the old winding. I'd say that's about the gage they used
too. After it's wound, either spray, or dip it in some polyurathane varnish,
and let it dry. Before the varnish though, check it for its self resonant
frequency. Short the coil out with a jumper wire, and use a dip meter to find
it's SR frequency. It's best to read the freq off the dip meter with a freq
counter. Just put a coil on the freq counter lead of several turns of wire and
hold the dip meter coil paralell to it. Where the dip is, is the SR frequency.
If its SR is on an operating band, just remove a few turns off the top and it
should move it to where it wont hurt anything. Check again with the dip meter
until it's right. If you dont want to mess with rewinding it, MFJ-Ameritron, RF
Parts, and B&W all sell plate chokes.
If the tank circuit coil dont look like it's been cut on, and all there, I'd
just try replacing the 15 meter tap and give it a smoke test. You should see
where the original tap was soldered on the tank coil. 15 meters will be just on
the large coil, or where it just drops down in size if they're using two
diameters of coil conductors. The large coil is for 10 meters toward the Tune
C. generally where the large and small coil meets is about where 15 meters is
at on some amps. Under 15 meters, the conductor that the coil is made with dont
have to be as large in diameter due to the skin effect (lower freq current
moves toward center of conductor). Some amps though use the same conductor,
usually copper tubing for the entire tank coil. If so, you'll have to find
where it was soldered if that's the case. It will be towards Tune C though.
Best,
Will
*********** REPLY SEPARATOR ***********
On 2/12/06 at 4:15 PM Scott Townley wrote:
>More info:
>1. By "tampered with" it looks like someone rewound the choke to skip a
>couple of turns right in the middle. There is some silk thread holding
>the
>choke together at top and bottom--never seen that on a commercially-made
>choke.
>2. The 15m switch contacts *appear* OK. They may have been replaced, but
>there's no charring or other evidence of nasties on the wafer itself. You
>can see where the tap used to be soldered to the coil.
>3. Not related, but as an aside...I did (gently) try and run the amp up on
>17m using the 20m position, but no workee. The input circuit doesn't tune
>anywhere near to 17m, which surprised me. I haven't opened it back up
>again to see if maybe someone else changed the L-C ratio in the input
>circuit or what.
>
>I'm tempted to just replace the 15m tap and go for it, I just didn't know
>if there was some known issue with the nominal choke on 15m. Or maybe I
>should just replace it with a B&W 802 or a National R-175A.
>
>
>
>
>
>>On 2/12/06 at 2:17 PM Scott Townley wrote:
>>
>> >Can someone on the list send me a photo of the "original" plate choke on
>> >the BTI LK-2000HD? I don't know if the non-HD is the same but if so
>that
>> >will of course do.
>> >My choke looks like it's been tampered with, and the 15m bandswitch
>> >position is missing its strap to tap the inductor. Not sure if someone
>> >went chasing down some choke suckout or what, but it would be nice to
>know
>> >the starting position.
>> >Thanks,
>> >
>> >
>
>
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