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[AMPS] Cathode Current

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Subject: [AMPS] Cathode Current
From: (Jon Ogden)
Date: Wed, 25 Mar 98 19:05:09 -0600
Ok, there has been a LOT of discussion lately about tube input impedance 
in a grounded grid amp.  So some of you are tired of it, big deal.  I 
belong to this mail reflector becuase I am trying to improve my skills 
and increase my knowledge.

My question is on what is the value of the cathode current in a GG amp.  
According to Ohms Law, Pin = (Ic^2)*Z.  Where Pin=Input Power, Ic=cathode 
current and Z=input impedance.  

>From Eimac's data, the driving impedance of a 4-1000A is 110 Ohms at a 
plate voltage of 5 KV.  Therefore, with Pin=90 Watts I would calculate Ic 
 to be the SQRT(90/110)=.90 A.  This seems like a big value but I am 
assuming that what goes in to an amp must come out so if the plate is 
running then at 650 mA (per spec) then the total grid current would be 
250 mA.  But maybe this is a wrong assumption (to add the currents) 
becuase the Eimac data shows the screen grid current to be 55 mA and the 
grid current to be 115 mA or a total of 170 mA.  So therefore, I am short 
80 mA somewhere.  Is that 80 mA effectively dissipated as heat or what.  
Or am I completely flawed in my assumption of what goes in must come out. 
 I have a feeling I am.

No flames please.  I am genuinely trying to learn some stuff here and I 
don't feel like going and digging through old text books.

Thanks for the help.



Jon Ogden

"A life lived in fear is a life half lived."

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