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Re: checking bias on single-ended EL84 amp


 
5/29/2000 4:02 PM
Bruce
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Re: checking bias on single-ended EL84 amp
OK as Jason said, your actual plate voltage is the plate voltage minus the cathode voltage, or 269vbdc.  
269vdc X .045ma = 12.1 watts.  
Prett much perfect for a single ended EL84.  
If you are worried about the current, you can increase the cathode resistance a little to get it down to 40ma or so.  
I'd leave it just like it is and limit the screen current at idle to a couple ma or so.  
 
Since the voltage drop across the 154ohm cathode resistor is only 7v, Ohm's Law, (I^2xR=P) or (ExI=P) would reveal that, at idle and no signal, the resistor is handling only about, .3watts...  
.045a^2 x 154ohms = .312watts or  
.045a x 7v = .315watts.  
(your 7 volts was not dead accurate)  
Nearly exactly the same answer two different ways though.  
So, a one watt resistor would work fair and a two watt resistor would probably last forever at twice the .3watt power loading.  
 
Bruce
 
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