At 2500 ohms reactance of your rfc, the TUNE capacitor probably won't have
the range because the rfc is now part of the matching network. And you will
go what is wrong with this picture. I have been there and done that!!! Ten
times XL is a good number. All design data assume the rfc has infinite XL.
The RF choke is really not a very high Q inductor and will dissipate a fair
ampont of power if XL is not very high.
Most designers don't understand this. (If you can them designers).
Don't go there especially on 160. I have an HP4815A Vector Impedance Meter
and it really opened my eyes to what is really going on. Get the RF choke
reactance as high as you can at 160 or wherever you are starting at. Sweep
the frequency range you want to use and watch for series resonances. The
plate rfc is one of the most critical elements in a high power amp.
73 Hardy N7RT
----- Original Message -----
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
To: <amps@contesting.com>
Sent: Monday, October 12, 2009 4:43 PM
Subject: Re: [Amps] Checking Plate Choke resonance
ORIGINAL MESSAGE:
On Mon, 12 Oct 2009 15:04:06 +0200, "DF3KV" <df3kv@t-online.de> wrote:
>I have never seen such high impedances at amplifier chokes.
>Most of the chokes in ham radio amps are not even twice the plate load.
>The famous Rfparts 225µH transmitting choke is just 2,5k ohms on 160m.
>Much smaller chokes are used in commercial amplifiers.
REPLY:
You are right, I mis-spoke. I should have said ten times the reactance of
the
plate tune cap, not times the plate load impedance.
Sorry. Need more coffee. :-)
73, Bill W6WRT
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