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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|