>
>Hi Gang..
>
>I've seen a lot of good advice metered out here, and quite a few problems
>solved....so here goes with my present headache.
>
>I've just finished a 4CX800 2 Meter linear...it's a near copy of the
>JH2CLV device, but with a "standard" slab line anode with flapper tuning.
>The plate line is U Shaped with a sliding assembly with fingerstock at the
>earthy end of the line to couple the RF out to the world.The line bends
>around from the DC Blocking Caps to adjacent the Socket where it is
>earthed..makes for a short RF Box. The Tube end has two 330pf Doorknobs
>attaching it to the Tube.
** Paralleled DC blocker caps unavoidably create a parallel-resonant
circuit. I would use a dipmeter to see where this resonance happens to
be parked.
- I would use one capacitor for the DC blocker. For 2m coupling, 50 -
100 pF would be my choice. For effectively bypassing 2m, C should
probably be no more than 250pF to avoid operating the capacitor above
it's self-resonant freq.
>
>DC conditions are 1850 on the Anode ( when tuning with constant carrier),
>350v on the Screen and the grid bias set to give 150ma idling current. All
>the above is controlled/supplied by G3SEK Boards.
>
>The thing fires up no problem, but going to Tx and injecting some rf drive
>yields little in the way of output. After much swearing and testing which
>involved putting a 2k resistor across the Anode/Screen and looking into
>the Output connector and checking for resonance on 144.200 and tuning
>up/down to make sure I had the line the right length and a low SWR, I can
>only get about 120w out with 6w of drive.The thing "peaks" the rf when the
>anode flapper is tweaked, and the flapper sits at about 5mm off the plate
>line when it is tuned. Sliding the output coupling up and down its
>travel, from furthest away from earth towards earth, yields max output as
>I approach the earthy end of the line, but the screen current does zilch.
>
>When I have max output, I'm looking at about 680ma Ip, very little in the
>way of screen current ( the needle hardly moves) and a big kick
>"backwards" on the Grid Meter...Yep, it attempts to go negative,
** Which way is the grid-I meter polarized?
cheers, Glenn.
>and the
>more drive, the more energetic it becomes.Incresing drive see's more rf,
>but lots more Ip.
>
>A fellow Ham has one the same...and his works fine. I copied his
>construction details accurately ( I hope ) and the above is the result. My
>Amplifier learning curve is steep, and going more vertical. This thing is
>on wheels and I live on a hill...any ideas before I give it a push ??
>
>73
>
>Glenn
>VK4TZL
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