[Amps] !44Mhz Gi7B amp problems continued

[jeff millar]

Sean Williams wrote:

>Hi All,
>
>I have just finished this amp, built to a YU1AW design.
>
>It used to oscillate at 480 megs, this has now been cured, however, it 
>no longer produces anywhere near the power it used to - Previously I 
>could achieve 800 watts for about 40 watts of drive.
>
>Now I struggle to get 150 Watts before the grid current shoots through 
>the roof - anode current never rises above 300 ma at 2.2kv.
>
>I have tried a different pair of tubes, and still get the same results.
>
>Any ideas??
>  
>
Sean

Is this the design at http://nd2x.net/yu1aw/GI7B-2m-LB-skem.GIF?
What did you use for the output tune and load capacitors?
Does the output tune exhibit a sharp dip with some peaking of output?
At about what tune capacitance does the output dip?
At abotu what load capacitance does the output peak?

I agree with the previous comments about the tube having too light a load.
The design can miss it's match quite easily for a number of reasons

    * The inductor isn't quite the right value
    * Different stray capacitance than expected
    * Stray inductance in the capacitors.

I've got some experience comparing the way the tuning controls work
and what's happening on a smith chart and might be able to help you
figure out which way to adjust the coil, up or down in inductance.

I'm thinking about building a similar amp and working with you on this
will teach me some stuff.

jeff, wa1hco

>Sean
>M1ECY
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