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[AMPS] go figure

To: <amps@contesting.com>
Subject: [AMPS] go figure
From: philk5pc@tyler.net (Phil Clements)
Date: Mon, 28 Jun 1999 18:51:10 -0500


>-> There is another major jump in components used as capacitors. HF
>> amplifiers need a lot of C for blockers to handle 160 meters. 
>
>Most amps have way more than enough C for 160. The largest 
>problem is generally current rating on 30 MHz, not C on 160.
>
>If you calculate the amount of C required to not disturb the anode 
>impedance, you be amazed how small it can be compared to what 
>everyone uses.
>
>Let me second what Tom wrote above.  I used a 150pF, small fixed Jennings
>vacuum cap
>as a plate blocker on a number of kW amps, ran the calcs he referrs to,
>and I can assure the gang that it really worked extremely well on 14mHz. 
>I made a test, using the conventional pair of 1000 pF 858s, and found no
>difference at that frequency.  Vacuums will beat the ceramics every time,



After converting and canabalizing numerous industrial amps that
are VERY overengineered due to their continuous duty requirements,
I came up with a rule of thumb for plate blocking cap values without
having to do a lot of computations each time you "roll a new one."
I have used 10 pf per meter. IOW, 100 pf for 10 meters and 1600 pf
for 160 meters. I agree with Tom and Marv, and this also is probably
a bit of overkill, but it is simple to remember, and errs on the 
conservative side. As previously stated, one needs to check the
cap for heating after a healthy smoke test on 10 meters..

(((73)))
Phil, K5PC



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