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odd coil




 
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KA9EGW
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« on: January 12, 2015, 02:41:59 PM »

so today the delivery guy dropped off my new coil, it is from a bc tx, huge, about 4" ID and a foot long, and is edge wound, it is probably a hundred micro Henry or better...and it has two rods running up through the middle of it with a sliding doohickey about 2" diameter and 2" long, on a plastic chain...it slides on the two rods so it cant rotate and even though its hollow like a giant fuse cap the rods go through so you can't stick anything up inside of it.
I understand the coil, its purpose is to inductify, but what's with the doohickey? is that supposed to be a tuning slug?
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KA9EGW
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« Reply #1 on: January 12, 2015, 03:10:00 PM »

Pic of coil


* 14210932792841264706054.jpg (1099.35 KB, 2592x1456 - viewed 935 times.)
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KA2DZT
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« Reply #2 on: January 12, 2015, 03:52:12 PM »

Well if it's made from brass which it probably is, it a tuning unit which sort of shorts out some the turns (even though it doesn't make any contact with the coil) when moved into the coil.  This is my first guess but I'm sure someone here knows exactly what it is.

Fred
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Steve - K4HX
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« Reply #3 on: January 12, 2015, 06:34:19 PM »

I think you have it Fred. It looks very much like a coil out of a RCA BTA-1MX or BTA-500MX. Those have a brass insert like the one pictured that is used for tuning.
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KA9EGW
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« Reply #4 on: January 12, 2015, 06:53:07 PM »

So if I'm using it in an amplifier tank tuned by air or vacuum variable(s) I can remove the insert and its support rods.  Anyone got a need?
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Steve - K4HX
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« Reply #5 on: January 12, 2015, 07:41:23 PM »

Yes, you can remove it.
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KA9EGW
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« Reply #6 on: January 12, 2015, 08:50:20 PM »

If anyone here has a need for it they can have it for the cost of shipping...
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KA9EGW
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« Reply #7 on: January 12, 2015, 09:22:31 PM »

Update: apparently (read: seller said) it's a Johnson 200-411-2
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W7TFO
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IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


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« Reply #8 on: January 13, 2015, 12:24:08 AM »

That tuning scheme was pretty slick. 

No contacts to burn like a roller. 

No shorted turns eating up power. 

Used a fixed cap for simplicity.

As the brass slug went in, the inductance was lowered.

73DG
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Just pacing the Farady cage...
KA9EGW
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« Reply #9 on: January 13, 2015, 09:59:57 AM »

Oh, indeed!  But how amenable to covering 160-10?  HI!
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WQ9E
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« Reply #10 on: January 13, 2015, 10:03:58 AM »

I agree that is a neat tuning scheme and even when used with switch taps it would provide easy fine tuning of the inductance value.

Many of the old alignment tool sets included a "magic wand" that had a brass slug in one end and a ferrite slug in the other.  Inserting either end into a properly adjusted coil would result in decreased output, an increase indicated alignment needed attention.
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Rodger WQ9E
KA9EGW
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« Reply #11 on: January 13, 2015, 10:06:23 AM »

I think I may have one of those wands...
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WA2SQQ
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« Reply #12 on: January 13, 2015, 10:40:03 AM »

I agree that is a neat tuning scheme and even when used with switch taps it would provide easy fine tuning of the inductance value.

Many of the old alignment tool sets included a "magic wand" that had a brass slug in one end and a ferrite slug in the other.  Inserting either end into a properly adjusted coil would result in decreased output, an increase indicated alignment needed attention.

Yup! I have one and often wondered why more people don't know about these.
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Opcom
Patrick J. / KD5OEI
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« Reply #13 on: January 14, 2015, 01:07:15 AM »

There's a 3CX3000 amp on the www for 6M using 2-3 turns of pipe and a kind of cylinder like that. My guess it is best for single band tuning.
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