[Amps] !44Mhz Gi7B amp problems continued

[TexasRF@aol.com]

High grid current with low plate current usually means the output circuit  
needs heavier coupling to the load. Said another way, the plate load impedance  
set by the output network is too high. 
 
The YU1AW 144 MHz designs have an L network for output matching with a  
flapper style series capacitor to the output load. To increase loading, you  
increase the output coupling capacitor value (closer spacing) and the plate  tuning 
capacitor will need less capacitance (wider spacing) to maintain  resonance.
 
The load needs to be near 50 ohms resistive for all this to work properly.  
If there is series +-j, these values will add/subtract from the series coupling 
 capacitor value and have an effect on the plate load impedance.
 
A typical tuning procedure is to tune the plate circuit for maximum power  
output which makes all of the above happen automatically. Of coarse excessive  
drive power will make the grid current too high when the unit is working  
correctly.
 
73,
Gerald/k5gw
 
In a message dated 8/21/2005 7:06:50 A.M. Central Standard Time,  
m1ecy at m1ecy.me.uk writes:

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
M1ECY
_______________________________________________
Amps  mailing  list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps