[Amps] hf-2500

Wed Dec 26 16:35:01 EST 2012

Thanks for that info Dave, I'll keep it in mind for when a fried critter 
arrives.

Carl
KM1H

----- Original Message ----- 
From: "K1TTT" <K1TTT at ARRL.NET>
To: <amps at contesting.com>
Sent: Tuesday, December 25, 2012 7:45 AM
Subject: Re: [Amps] hf-2500

> In the HF-2500 the ONLY failures I have had were on 40m and 80m contest
> RTTY.  On these amps half or three quarters of the turns are shorted on 
> the
> toroid on 80m and 40m respectively.  To make it worse they attached the
> toroid to the front of the pressurized compartment with 5 little holes
> bleeding some air out through the insulator and into the middle of the 
> core.
> Unfortunately the center of the core is mostly filled with a tecaform rod
> and then its capped with another piece so the air path is rather tight:
> http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx#hf2500m
> ods
> This is made worse on the newer ones like in the link above because of the
> bigger wire that he changed to.  The older toroids that have been ok so 
> far
> had a smaller wire that left more room for air to flow inside.  One of the
> worst ones actually damaged the core material so when I tried to reuse the
> core it broke (scroll down to 10/30 on the above page).   When you take 
> one
> of the melted toroids apart you will notice that the wrapping under the 
> wire
> is discolored where the 40m and 80m turns are, this is probably due to the
> higher currents in those concentrated over only part of the core, and its 
> at
> the top so all the heat rises to there anyway making it that much worse.
>
> If you scroll down to 11/12 you will see the final fix for making it work
> well on 80m.  The tuning with the improved coil is much better and drive
> levels are lower and it is cooler than the original... but of course it 
> only
> works on 80m now.
>
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://wiki.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://k1ttt.net
>
>
> -----Original Message-----
> From: Carl [mailto:km1h at jeremy.mv.com]
> Sent: Sunday, December 23, 2012 15:18
> To: Larry Benko; amps at contesting.com
> Subject: Re: [Amps] hf-2500
>
> 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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>>
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