Jim, I would try a small air wound coil similar to what you would use in a
parasitic suppressor in series with the toroid, maybe in the lead to the
switch.
Dan, N5AR
On Fri, Mar 21, 2014 at 4:46 PM, Jim W7RY <w7ry@centurytel.net> wrote:
> Both leads are shored by the band switch when on 10 meters guys.
> Interesting that 3 of you came up with the same possibility...
>
> Not sure where to put the capacitor if both leads are shorted together.
> Perhaps I could center tap the toroid (bare the Teflon wire) and solder a
> cap from the center tap to one of the output leads.
>
> I removed the toroid and the major heat in the 3 turns of wire is where
> the winding is within 1/4 inch of the vacuum loading cap. Which is probably
> to close.
> See:
> http://s900.photobucket.com/user/w7ry/media/8877%20Amplifier/P1010217.jpg.html?sort=3&o=16
>
> I was simply going to move it away from the loading cap and see what
> happens. I was also thinking of install a wire coil. I have a ceramic coil
> form that would work. 30 turns, 2"dia 3.5" long which is 20uH. I have room
> to mount this.
>
> Thanks all!
> 73
> Jim W7RY
>
>
> *From:* Dan Hearn <n5ardxcc@gmail.com>
> *Sent:* Friday, March 21, 2014 3:02 PM
> *To:* Jim W7RY <w7ry@centurytel.net>
> *Cc:* AMPS <amps@contesting.com>
> *Subject:* Re: [Amps] More on Toroidal Tank Circuit Issues
>
> 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
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
> --
> Dan Hearn
> N5AR
>
--
Dan Hearn
N5AR
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