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Re: [Amps] Output Matching Network, Need Advice

To: "'KB0NLY'" <kb0nly@mchsi.com>, <amps@contesting.com>
Subject: Re: [Amps] Output Matching Network, Need Advice
From: "Evert Bakker \(PA2KW\)" <evert@pa2kw.com>
Reply-to: evert@pa2kw.com
Date: Thu, 26 Feb 2009 00:51:08 +0100
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Hello Scott,

Make sure the plate coil has the value (pre-described measures) and try to
get the capacitor in the required range. I know Drago (YU1AW) designs his
amps with a very high Q unloaded and low Q in loaded situation as to make
the amp stable (no temperature effects) and easy tuning.

If you build a mono band amplifier he says: Tune the amp once, and burry it
in concrete as you will never have to re-tune (when the load stays the same
of course).   

I build 4 amps with absolute maximum results!

73's, Evert PA2KW



-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of KB0NLY
Sent: Thursday, February 26, 2009 00:36
To: amps@contesting.com
Subject: [Amps] Output Matching Network, Need Advice

Gents,

As some here are aware, i am building a 6M amp using a GI-7B Triode.  I
constructed the amp from a combination of info from YU1AW and a few that
have actually built his design.

Today i am trying to finish building and adjusting the output network.  I
borrowed an MFJ analyer and put it on the output, calculated the value of
the resistor i should put from the anode to chassis using all the info and
references you guys provided and that should be a 2200 ohm, or 2.2k
resistor, tripped the t/r relay and started working on it. I could't get the
SWR meter to go below infinity, and the resistance would adjust over range
of 20-100 ohms with the load cap.  So i removed some plates from the plate
cap, slowly only pair at a time until i started seeing a dip in SWR as i
tried it each time.

I got down to the last four plates, four on the stator four on the rotor,
and i wanted to stop and ask some questions before i take off any more as
its a destructive process with the air variable i have and i can't put them
back if i mess up!  I found some references that said i should go up and
down in frequency from my target frequency and try adjusting it each time to
find out where its resonant.  I found through trial and error that i could
get it totally flat, 1:1 and 50 ohms, at 40Mhz.  So i need to go up in
frequency.

The questions..

Should i remove more plates from the tuning cap to bring up the resonant
frequency?  I think i might still be too high in value, most designs online
show around 5-30pf for it and i probably don't have it that low yet.

Or should i make a change to my plate coil?  I have that at 4 1/2 turns of
10awg wire, spaced less than the thickness of the wire apart at roughly 1
1/8" inside diameter.  That was the tightest and closest i could get it to
the specs online.  I tried changing the gap on the turns, more and less, and
it didn't seem to affect it any.

73,

Scott KBØNLY

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