I have a 2500 on the bench right now and there is no sign of overheating.
The owner uses it strictly on 75 SSB which might explain it but the amp
easily puts out 2200W +.
Perhaps different gauge wire was used during production, this one has blue
#12 stranded silver plated Teflon and is a 1996 build. Ive worked on several
others and dont remember wire size but the insulation was black. The skinny
braid used to go to the switch probably doesnt help either. Those were all
earlier models and the toroids were fine from even contest use.
IMO it is a fine CW/SSB amp and like many others should be derated for RTTY.
The transformer isnt that robust anyway.
Carl
KM1H
----- Original Message -----
From: "Larry Benko" <xxw0qe@comcast.net>
To: <amps@contesting.com>
Sent: Saturday, December 22, 2012 11:25 AM
Subject: Re: [Amps] hf-2500
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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