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Re: [Amps] Alpha 86

To: "Vic Rosenthal" <vic@rakefet.com>
Subject: Re: [Amps] Alpha 86
From: R.Measures <r@somis.org>
Date: Tue, 25 Nov 2003 02:56:05 -0800
List-post: <mailto:amps@contesting.com>

>R. Measures wrote:
>
>> 
>>>lou de beer wrote:
>>>
>>>
>>>>Anyone own an Alpha 86...I have a question regarding the bandswitch.....
>>>
>>>I just replaced a bandswitch wafer on one.  ...
>> 
>> 
>> ***  Vic --  I would like to buy the old bandswitch wafer from you if you 
>> are willing to part with it.  I am also looking for kaput 3cx800A7s.   tnx
>> -  If anyone else has some of these items, please name your price.  
>
>I will be happy to send it to you at no charge, Rich.  

**  Tnx, Vic.

>I think the 
>question "why did this burn out" is interesting, because I know the 
>individual who was operating it when it happened, and he did not 
>hot-switch it.  He was attempting to load an 80-meter coax-fed dipole on 
>160 meters (it was late, in a contest, etc.).  The contacts which burned 
>were used to switch padders in parallel with the loading capacitor of 
>the Pi-L output circuit.

**  But how did the 160m Load-C padder contacts arc if they were closed?
>
>The question then is, "Why didn't the amplifier trip off from excessive 
>SWR?"  My theory, which I will happily hear attacked or supported, is 
>the following:
>
>The amp doesn't exactly trip on SWR, it trips on reflected power.  My 
>sleepy friend found a setting of the controls which was highly 
>underloaded, producing a very high circulating current in the tank 
>circuit, and very little power out (and hence very little reflected 
>power).  The current was enough to burn the contacts.  

**  The contacts burned while closed?

>He probably was 
>not driving it very hard, or it would have tripped on grid current.

**  Was he using an antenna tuner to match the few-ohm antenna to the 
50-ohm amplifier??
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