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Re: [Amps] DC Blocking Capacitor

To: Phil Clements <philc@texascellnet.com>
Subject: Re: [Amps] DC Blocking Capacitor
From: Gary Schafer <garyschafer@comcast.net>
Reply-to: garyschafer@comcast.net
Date: Wed, 27 Apr 2005 11:57:27 -0400
List-post: <mailto:amps@contesting.com>
Phil,

Am I looking at this backwards or are you?

Thanks
Gary  K4FMX

Phil Clements wrote:
> Amen, "R"! I think that so many guys over the years used whatever they had
> in their junk boxes that looked big enough that a proliferation took place.
> Sort of like parasitic suppressers...if they worked fine on tube type A they
> should work okay on tube type B.
> 
> A typical amp running max. smoke from a pair of 3-500Z's or a single 8877
> works out to a plate resistance of around 2200 ohms or so. Plugging in the
> formula, 5% of this means we need a capacitive reactance in our C/Block of
> around 110 ohms @ 1.8 mhz. Your understanding of 200 pf is enough is
> correct, as a 200 pf capacitor would have a reactance of around 440 ohms on
> 160 meters. At a lower plate load impedance, say 1000 ohms, you have even
> more headroom. You would have to exceed 8000 ohms plate load impedance to
> get even close to exceeding the 5% requirement with a 200 pf cap.
> 
> (((73)))
> Phil Clements, K5PC
> 
> 
> 
> 
> 
> 
> Subject: Re: [Amps] DC Blocking Capacitor
> 
> The value of the DC blocking cap is seeming less critical than is 
> commonly thought.  As I understand it, in most HF amplifiers, 200pF is 
> enough.  However, the I-handling ability become important on the 28MHz 
> band since most of the tank circulating-current passes through the DC 
> blocker on its way to and from the anode..
> 
> On Apr 26, 2005, at 12:26 PM, Bob Easterbrooks wrote:
> 
> 
>>Gentleman, What determines the capacitive value of the DC blocking 
>>capacitor
>>used in a convential shunt fed PI, and can the same rules apply to a 
>>simple
>>link coupled tank circuit?   I thank you in advance.  Bob, K6JQA
> 
> 
> 
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> 



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