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 Post subject: info needed for B & W coil form
PostPosted: Jul Wed 15, 2020 4:38 pm 
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Joined: Apr Thu 12, 2007 3:24 am
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Location: Milwaukee WI 53219
I want to build a VFO for my small Babcock MT-5B transmitter. Neither a google search or the B & W website shows the Miniductor #3102 that the schematic calls for. Does anyone have info on that form size or was it a misprint? I'll find something similar in size to wind my own if I can get a ballpark size for that form. Otherwise I'll search for a calculator online to find the value and just wind it on whatever form gets me close to the uh value.


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Wed 15, 2020 4:51 pm 
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The 3102 coil is not the Airdux style


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Wed 15, 2020 5:55 pm 
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Location: Milwaukee WI 53219
Thanks. I think I have a 5 pin tube socket. I can approximate the size of the coil if the drawing is close to scale between coil and socket.


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Thu 16, 2020 11:41 am 
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Location: Perrysburg, OH, 43551 U.S.A.
I'm not sure that the coils being used are the plug-in type simply because the parts list is calling for a certain number of turns while the types N2LXM is showing are. Usually, when a project called for a certain Miniductor P/N and a certain number of turns, the intent was to buy a coil like one of these https://www.bwantennas.com/Mini.html and cut it for the number of turns called for (plus enough extra to bend for making connections). The OP's schematic looks like it's calling for direct connections to the switch and tuning caps.

If someone could nail down the coil dimensions, this article would prove useful in winding your own: http://www.arrl.org/files/file/Technology/tis/info/pdf/9708033.pdf

John

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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Thu 16, 2020 11:36 pm 
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Location: Sullivan, MO
Could the middle numbers have been transposed and it should actually be a 3012? That is 3/4" diameter, 3" long, 32 turns per inch.

https://www.bwantennas.com/Mini.html

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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Fri 17, 2020 3:25 pm 
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Joined: Mar Sat 08, 2008 3:21 am
Posts: 619
Location: hillsborough, nc
Miniductor stock was a ubiquitous component decades ago and wasn't wildly expensive, like the current ad shows.
With the info above, you can compute the inductance of any specified length of stock and use the inductance formula to compute how to use a form you have.
You can also compute the capacitance required to tune it to any frequency you want.
Winding coils is rewarding. They look neat and you can use all manner of stuff for forms: pill bottles, toilet paper tubes, oatmeal cans, plastic pipe, dowels, old tube bases.
Get busy,
WL


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Fri 17, 2020 6:43 pm 
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Joined: Apr Thu 12, 2007 3:24 am
Posts: 2374
Location: Milwaukee WI 53219
Since there was no definitive info for the original coil form I'll wind one with whatever I have laying around. I just need to make sure it's rigid for frequency stability. I bookmarked a site for figuring the inductance and capacitance I need. There are lots of them out there.


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Fri 17, 2020 8:16 pm 
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Joined: Mar Sat 08, 2008 3:21 am
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Location: hillsborough, nc
What do you mean no info?
3/4 32 24 10

3/4" diameter, 32 tpi, 24 ga wire

I'd use heavier wire for a VFO coil and keep it away from the heat of the tube.

WL


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Fri 17, 2020 11:19 pm 
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Joined: Apr Thu 12, 2007 3:24 am
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Location: Milwaukee WI 53219
Read carefully. He gave the info for a 3012 form in case the numbers in my schematic were a misprint. I'm looking for 3102 if such a thing exists. So his answer is a possibility but not definitive.

But it doesn't really matter. I've got my tank values and now I'll wind one up using thick wire. Thanks for help guys. I'll post results.


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Tue 21, 2020 2:39 am 
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Here is some 3012 stock, shown with the 44 cents it cost, for scale.


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 Post subject: Re: info needed for B & W coil form
PostPosted: Jul Tue 21, 2020 2:52 am 
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Joined: Mar Sat 08, 2008 3:21 am
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Location: hillsborough, nc
3102 IS a plug in coil, as seen in old catalogs.
WL


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