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Re: [Amps] pi-net spreadsheet question

To: <dezrat1242@yahoo.com>, "Amps reflector" <amps@contesting.com>
Subject: Re: [Amps] pi-net spreadsheet question
From: "Carl" <km1h@jeremy.mv.com>
Date: Thu, 8 Apr 2010 10:08:34 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
> ORIGINAL MESSAGE:
>
> On Wed, 7 Apr 2010 16:02:14 -0400, "Carl" <km1h@jeremy.mv.com> wrote:
>
>>Not really. Even a 2W carbon takes decades when the suppressor is designed 
>>and not just shotguned.  Modern resistors dont >change at all....yet.
>
>>If it decreases to a low enough value, guess what? No suppressor.
>>
>>Thats not the change direction. And below a certain value it will burn up
>>and tell your nose about it.
>>
>>
>> If the
>>> resistor increases value enough, same thing. No suppressor.
>>
>>You wont live long enough for that to happen.
>
> REPLY:
>
> I don't know what planet your carbon resistors come from but I have
> spent much of my adult life changing low-value high wattage carbon
> resistors, and I guarantee you they can change in either direction, up
> or down.


Apparently your experience is rather limited. Yes they can go down but from 
RF heating and overvoltage the common course is up.  You might want to add 
that to your tech notes file.


>
> Metal-film and metal-oxide types are much more stable, but carbons are
> still in use out there and folks are still using them in parasitic
> suppressors.
>
> 73, Bill W6WRT

And will continue many more years Im sure. Yesterday I checked a pair in a 
1983 date code HL-2200 and the marked 47 Ohms had made it to 53 Ohms for 
both. Not bad for 27 years considering they are 10% tolerance.

Carl
KM1H
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