[Amps] hf-2500

[Larry Benko]

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
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>