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
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