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[AMPS] Tuning of amps - 3cx800s,etc..

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Subject: [AMPS] Tuning of amps - 3cx800s,etc..
From: (Rich Measures)
Date: Sun, 15 Mar 98 12:35:50 -0800
>In a message dated 98-03-15 11:04:39 EST, you write:
><< Increasing the load setting  [less C2]  beyond that which produces 
> optimal power transfer decreases the step down transformation ratio of 
> the tank, which means that the 50 ohm load now look too low for the way 
> the tank has been adjusted.  .  >>
>Next lesson.......
>Ok Rich, I understand the C2 being less and the antenna system load being

Not quite.  The antenna load is still 50 ohms, however, by decreasing C2 
a bit, the output R of the tank is raised to perhaps 70 ohms, whereupon 
the 50 ohms is a relatively too heavy load for the way the tank is 
adjusted, so power transfer is less than optimal --i.e., a mistune.  .   
>However, are you saying above that this method of dropping the grid 
>current is incorrect, even if I re-tweak (for max pwr) the Plate C at that 
point ??  

No.  For a Class AB2, cathode-driven amplifier, the correct amount of 
grid current is obtained when the tune and load are set to produce the 
most RF output, provided that the anode current rating is not exceeded -- 
i.e., the tube is not over-driven.  
- Eimac publishes no maximum grid-current rating for high Mu triodes, nor 
recommends  specific grid currents.  The bottom-line is that when a 
maximal amount of RF current is flowing in the output hose on the back of 
the amplifier, not too many electrons are left over to be flowing down 
the grid wires.  When too many are siphoned off into the grid due to a 
mistune,  RF output drops  (provided that the amplifier is not being 
later, Eric


R. L. Measures, 805-386-3734, AG6K   

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