I used to think that shorted turns on powdered iron toroids was bad
until I did some tests. My tests were not exhaustive but winding some
#12 wire on a T200-2 core and shorting out some of the turns to reduce
the inductance to ~1/2 of the inductance with the turns not shorted
showed a moderate reduction in unloaded Q and a slight increase in
temperature rise but nothing hugely significant.
I concluded that if shorting turns on an air core (u=1) was fine and
shorting turns on a 60Hz transformer (u=10000 or more) was really bad
then shorting turns on a powdered iron core (u=6 to 10) was much closer
to the air core case than to the u=10000 case.
Of more importance is that toroidal cores are not easy to cool since
they usually get connected to the chassis with an insulating washer
beneath them and air flow not that good. Perhaps this leads to some of
the reported failures.
73,
Larry, W0QE
On 12/19/2012 6:16 PM, Jim W7RY wrote:
Bill
We already had this discussion on here about a year ago. But I 'm
going to repeat it.
Alpha, Ameritron, Jerry K8RA, myself W7RY, and many others all use
toroids with shorted turns on our "L" coil in a PI-L circuit. It
works just fine.
Do you mean that a shorted turn toroid for the PI network is not
good? Or are you making a general statement that they don't work at
all in an amplifier?
73
Jim W7RY
-----Original Message----- From: Bill Turner
Sent: Wednesday, December 19, 2012 12:26 PM
To: Amps
Subject: Re: [Amps] hf-2500
ORIGINAL MESSAGE:
On Wed, 19 Dec 2012 17:15:03 +0000, K1TTT wrote:
Agreed, that is why I have modified one to do only 40-10m... removing
the
80m and 160m coils from the toroid removes the shorted turns problem and
makes it run very nicely doing rtty on 40m.
REPLY:
As David found out, shorted turns on a toroid or any iron core coil
are a no-no unless you do some very careful design and testing, which
Command obviously did not do. Shorted turns on an air core coil are
usually no problem. A word to the wise.
73, Bill W6WRT
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