Try shorting between one or two turns of your tank coil and re-try the
analyzer. No need to solder, just insert a nut or two between the coil
windings. I would not remove any more plates from the Tune capacitor; that is
not helping your case at all and may do more harm than good.
I just finished a 6 meter amp and wound up trimming my tank coil from 6 turns
to 3-1/2 before I got a good dip on the analyzer.
Good luck.
Russ
--- On Wed, 2/25/09, KB0NLY <kb0nly@mchsi.com> wrote:
> From: KB0NLY <kb0nly@mchsi.com>
> Subject: [Amps] Output Matching Network, Need Advice
> To: amps@contesting.com
> Date: Wednesday, February 25, 2009, 3:36 PM
> 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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