Great explanation!
Thanks for the knowledge and reasoning.
Gary…wa6fgi
Sent from Gary’s iPad
> On Feb 14, 2025, at 9:00 AM, amps-request@contesting.com wrote:
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> 1. Acceptable Swr for a tube amp without retuning.
> (jim.thom jim.thom@telus.net)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Fri, 14 Feb 2025 07:46:09 -0800
> From: "jim.thom jim.thom@telus.net" <jim.thom@telus.net>
> To: amps@contesting.com
> Subject: [Amps] Acceptable Swr for a tube amp without retuning.
> Message-ID:
> <CAB4ZMgvGh5mpDnccUTk6BVtX30LJKniqp0YUH6bC7AaES4X2-A@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
>> So could someone please explain or point me towards some books/articles
>> that talk about what happens exactly with voltages/currents at bad SWR?
>
> To keep it real simple, depending on coax line length, ( node /
> anti-node), the max voltage = sq root of the swr. IE: 2:1 swr. Max
> voltage = 1.41 x normal (1:1 swr) swr.
>
> 1500 watts into 50 ohm dummy load = 5.5 amps into 50 ohms = 275 Vrms =
> 386 V peak.
> With a 2:1 swr, rms voltage will rise to 386 vrms. Peak V will rise to
> 550 V peak.
>
> Max rms current will also be sq root of the SWR. Into a DL, that's 5.5
> amps with 1.5 kw and 1:1 swr.
>
> With a 2:1 swr, RMS current rises to 7.78 amps.
>
> You will not obtain max V or max I at the same time.
>
> It's average current that melts stuff.....and peak V that arcs stuff.
>
> Depending on power output, with typ tube amps, I would not go much past a
> 2:1 swr. Maybe 2.5:1 max.
>
>
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