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PostPosted: Sat Aug 24, 2013 8:26 am 
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Joined: Sun Feb 28, 2010 2:12 pm
Posts: 1547
I picked up a nice variable capacitor at the hamfest today. It has a built in reduction drive and an attached dial:
Image

Looking at the shape of the plates, it must be some sort of a straight-line capacitor:
Image

This could be the start of a nice receiver... a regen perhaps?


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PostPosted: Sat Aug 24, 2013 1:44 pm 
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Joined: Sat Jun 06, 2009 6:58 pm
Posts: 3244
Location: South Florida
That looks like the tuning cap from a BC-221 heterodyne frequency meter, widely used in WW2 and later (every B-17, B-24 and B-29 had one, which may give some insight into its origin). Hans Summers has some photos.

http://www.hanssummers.com/tubevfo/bc221cap.html

also: http://www.qsl.net/ve3bdb/Capbc221.JPG

IMO it's wasted in a regen. It makes an ideal tuning cap for a VFO. In fact, I think Roger, AB8IF, used one in one of his receivers.

73,

Jim

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http://kr1s.kearman.com/
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PostPosted: Sat Aug 24, 2013 3:22 pm 
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Bingo. Looks like a BC-221 unit.

Doing some reading about this unit, it seems like I did indeed get lucky, as this 50:1 tuning mechanism appears to be widely-praised. I'll probably be using this in a couple of projects, maybe using some kind of quick-release connectors on the cap so I can easily swap it among different circuits.


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PostPosted: Sat Aug 24, 2013 5:02 pm 
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Joined: Sun Nov 02, 2008 7:15 am
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Location: NJ, USA
KR1S wrote:
IMO it's wasted in a regen. It makes an ideal tuning cap for a VFO.
I think it is equally suitable for a high end wide coverage SW regen. Considering 100:1 reduction it needs a spinner type knob though :).


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PostPosted: Sat Aug 24, 2013 11:42 pm 
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Joined: Wed Oct 13, 2010 2:04 pm
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Location: Maryland
The capacitance range isn't enough to completely span the BC band but the 50/1 gear reduction drive performs very well in a wave trap.

Richard


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PostPosted: Thu Aug 29, 2013 6:27 pm 
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Joined: Sat Jul 20, 2013 4:22 pm
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It IS the tuning cap and drum of a BC221. I have an identical unit plus, I have a working BC221.

Dave


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