[Amps] 4CX800 2 Meter Linear

[R.Measures]

>
>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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