[AMPS] Smallest practical 1.5KW 20uH coil

[Michael McCarthy, W1NR]

I don't know if #25 is the number, but I'd also put 2 or 3 coats
of G-C Polystyrene Q-dope on the tape as well.

Mike, W1NR

"Richard W. Ehrhorn" wrote:
> 
> Hi Marv...
> 
> I'd go with the stacked T200-2 cores - Before winding, you can give
> yourself a bigger insulation margin of safety by wrapping the core stack
> with a couple of layers of Scotch/3M #25 fiberglas tape (can someone
> confirm that #25 is the right designation?) .
> 
> Don't know how you calculated it, but loss at 1.8-2.0 MHz should be almost
> unmeasurably small - anything over roughly 15W loss (1% or 0.04 dB at 1.5
> kW) would cause the toroid to run quite hot.  But in fact literally
> thousands of commercial amps have for decades used approximately the toroid
> inductor you describe without problems.
> 
> Good luck!
> 
> 73,      Dick    W0ID
> 
> -----Original Message-----
> From:   Radio WC6W [SMTP:wc6w@juno.com]
> Sent:   Monday, January 24, 2000 11:11 PM
> To:     amps@contesting.com
> Subject:        [AMPS] Smallest practical 1.5KW 20uH coil
> 
> Hello to the group,
>   I'm contemplating some alternative designs for a 20uH,160M "padder",
> coil, to be switched in following the Pi-net roller coil in my 4-400A amp
> under construction.
> 
>   The "typical" 3" long by 3" diameter section of B&W stock, including
> reasonable clearance to adjacent components, would take up a bit too much
> space in this instance.
> 
>   I thought of winding 20 turns of #10 teflon on four stacked
> (Micrometals / Amidon) T200-2 iron powder toroids but, that also gets to
> be rather large (2.25" diameter by 2.5" long) and is surprisingly lossy,
> if I did the math correctly.
> 
>   I'm now considering a short solenoid cross section wound in the form of
> two adjacent spirals (one spiraling into the center, the other out)
> fabricated from .375 by .07 silver plated copper ribbon.   Sixteen turns,
> 8 in each spiral, in a 3" diameter by just under 1" thick form factor
> should provide the requisite inductance.  I'll just slip some thin strips
> of fiberglass between the turns to keep them properly spaced.  The only
> drawback that I perceive in employing this geometry is the somewhat
> higher than usual inter-turn capacitance but, this part is only for use
> on 160M.
> 
>  Comments, suggestions, alternative ideas???  but, please no
> superconductors! :-)
> 
> 73,
>   Marv WC6W
> 
> *
> 
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-- 
**************** Give Every Man His Dew **************
Michael A. McCarthy, President
Everest Engineering Corporation, Consultants
4 Barnes Circle, Marlborough, MA 01752
(508) 460-6737, FAX (508) 460-7951
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