[Elecraft] my KPA1500 and 160M

[Bill Johnson]

Dave, Exactly my point.  Doesn't take long to cause the core to go south.  High voltage is fast. 

73,
Bill
K9YEQ

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of David Gilbert
Sent: Wednesday, September 2, 2020 12:37 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] my KPA1500 and 160M


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-wi
> th-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: elecraft-bounces at mailman.qth.net 
>> <elecraft-bounces at mailman.qth.net> On Behalf Of David Gilbert
>> Sent: Tuesday, September 1, 2020 12:28 PM
>> To: elecraft at mailman.qth.net
>> 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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