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previous: anonymous Here's the deal.... With 370 VDC on... -- 9/11/1997 3:07 PM View Thread

Re: WHO KNOWS THE MATH?

9/12/1997 10:02 AM
Mike T
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Re: WHO KNOWS THE MATH?
According to Funk on page 83 of his "Tube Amp Workbook", Volts x Amps = Watts.  
 
370V x .045 = 16.65 watts  
 
This is the way he puts it for cathode bias:  
 
He says:"The Maximum Plate Dissipation in a Class-A amplifier occurs at the Zero Signal Point. That's the idle point where the amp is at operating voltage, but has no signal running through it. The Plate Dissipation can be calculated by taking the Plate Voltage, multiplied by the Plate Current. The Plate Dissipation for a 6V6 is 12 watts. A 5E1 Tweed Champ runs at 305 Plate Volts, with a 470 ohm Cathode Resistor, and 19 volts expected on the cathode.  
 
19 volts / 470 Ohms = .040 Amps or 40mA  
305V x .040A = 12.2 watts  
 
You can use this type of calculation to determine the proper Class-A biasing for any amp. Remember. the tube will be biased at its full power dissipation AT IDLE. To understand this, remember that the input signal will drive the tube into higher power. AND THEN into lower power. The average power will remain at its maximum."  
 
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