[Amps] hf-2500

[Carl]

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 at comcast.net>
To: <amps at 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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