Re: my KPA1500 and 160M

Posted by David Gilbert-2 on Sep 02, 2020; 5:36pm
URL: http://elecraft.85.s1.nabble.com/OT-WWV-Time-Transmissions-tp7664561p7664611.html


No ... overheating doesn't take much time at all.

As I stated in my reply to Bill, high power and high VSWR will indeed
heat up a ferrite core device ... balun or common mode choke ... and it
can do so quite quickly.  In my case, I had a 160m Inverted-L that I put
up rather hastily for a contest and I didn't trim it for best match.  At
100 watts it worked fine because I could tune it at the shack, but at
anything above 1,000 watts the ferrite core in the common mode choke
would heat up and fault the amplifier (QRO Technologies HF-2500DX tube
amp) in less than two seconds. This happened repeatedly, and when I got
serious and fixed the antenna for a lower VSWR everything was stable
even at 1500 watts and even with the same choke that I luckily hadn't
permanently destroyed (although I suspect the core had been compromised
for original choking performance).

High VSWR is very tough on ferrite cores.

Dave   AB7E



On 9/2/2020 6:07 AM, Adrian wrote:

> Overheat is a situation taking time, and usually starts with a good
> match, then deteriorating.
>
> In this case ; "But when I throw the KAP1500 in line, it gets all
> pissed off, throws up and faults out.  Says SWR is 99:1 !!!"
>
> indicating an instant issue while the balun is still stone cold...
>
> The 5kw balun is not the best for your situation, but rather the 4116
> 3KW hybrid
>
> https://www.balundesigns.com/model-4116-4-1-hybrid-balun-1-5-54mhz-3kw/
>
> See ;
> https://www.balundesigns.com/blog/baluns-for-multiband-antennas-fed-with-open-wire-or-ladder-line/
>
> 73
>
>
> Adrian Fewster
>
>
>
>
>
> On 2/9/20 10:12 pm, Bill Johnson wrote:
>> I would agree that the coil could overheat.  The model number is left
>> out.  The Balun Design coil chosen may not be satisfactory for your
>> power despite the 5KW rating.  Which Balun are you using?
>>
>> Bill
>> K9YEQ
>>
>> -----Original Message-----
>> From: [hidden email]
>> <[hidden email]> On Behalf Of David Gilbert
>> Sent: Tuesday, September 1, 2020 12:28 PM
>> To: [hidden email]
>> Subject: Re: [Elecraft] my KPA1500 and 160M
>>
>>
>> One distinct possibility is that the 4:1 balun is getting hot at 1500
>> watts.  Have you tried running the KPA1500 at a lower power?
>>
>> 73,
>> Dave  AB7E
>>
>>
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