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
Sent: Friday, March 21, 2014 3:02 PM
To: Jim W7RY
Cc: AMPS
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
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Dan Hearn
N5AR
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