Jim, I think your 160 toroid when shorted is self resonant with its
distributed capacitance on 10m. You might be able to solve this by putting
a small cap across the 160 m toroid to move its self resonance.
73, Dan, N5AR
On Fri, Mar 21, 2014 at 1:08 PM, Jim W7RY <w7ry@centurytel.net> wrote:
> I may have to eat some crow here about using dedicated toroids on 160 and
> 80 meters...
>
> I built an 8877 amplifier based on the K8RA (SK) 3CX1500D7 amplifier.
> http://www.k8ra.com/index_049.htm
>
> Mine is shown here:
> http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/DSC_0037.jpg.html?sort=3&o=47
>
> And here:
> http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/P1010225.jpg.html?sort=3&o=13
>
> The lower toroid is 160 only and the upper one is 80 meters only (with
> 10,15,20 and 40 coils added in of course).
>
> I'm using a shorting band switch 6 position.
>
>
> On 10 meters, the 160 meter toroid (lower one) gets so hot, the fiberglass
> tape has turned brown, and the Teflon wire is melting the Plexiglas that
> the toroid's are mounted on.
>
> I know all about trying to use a tapped toroid for multiple bands is wrong
> (except on the L coil of the Pi-L circuit, and see my postings about the
> Commander HF-2500 and K1TTT's pictures of same) but WHY is the 160 meter
> toroid getting so hot when using 10 meters? It's mounted very close to the
> loading vacuum capacitor is the only thing that I can think of. But the
> weird part, is that this just started. During all of the testing, there was
> no problem, but now, its really getting HOT!
>
> When testing, I had the top cover off of the amplifier, now that I'm using
> it, the top cover is on. I'm going to try the test again with the top off
> and see what happens.
>
> On 80 and 160 meters, the toroids are normal temperature (around 100
> degrees) and everything works just fine since I'm not shorting turns on the
> toroids.
>
> Ideas?
> Thanks and 73
> Jim W7RY
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>
--
Dan Hearn
N5AR
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