Ok I know you take bias v/ resistor value = total Ma
take Ma and divide by 2 for each tube. so now you have the Ma for each.
So the question is do I subtract any Ma for heaters or anything. i've heard that you need to subtract something to get true values.Aslo say i get 12 watts per tube.Will the total output be 22watts.
Question about finding wattage
Moderators: zaphod_phil, Daviedawg, Graydon, CurtissRobin, colossal
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Jason
Calculation of Plate Power Dissipation + Watts RMS
John,
Plate Dissipation [Watts]=Plate Voltage [Volts] X Plate Current [Amperes]
1. Measure plate voltage [DC]--I like to use the shunt method and/or Randall Aiken's method of measuring voltage drop across the primary and converting to current. See http://www.aikenamps.com/
2. Measure plate current [Amperes]--Make sure you convert Milliamperes to Amperes--divide Milliamperes by 1000 to get Amperes. EX: 20 milliamperes X 1000=.02 Amperes
3. Measure cathode voltage [DC]
4. Subtract the cathode voltage from the plate voltage--don't forget this step if you are biasing any cathode biased amp. EX: 330VDC plate volts - 15VDC cathode voltage = 315VDC effective plate voltage
5. Multiply effective plate voltage by plate current. EX: 315VDC X .020Amperes = 6.3 Watts
That is how much heat your EL-84 plates are dissipating. The maximum heat dissipation EL-84's are designed for is 12 Watts.
Watts RMS at clipping Measurement--do this after you verify the bias:
1. Attach a dummy load [big resistor] to match your Output transformer secondary tap [4,8,or 16 Ohm]. I like the Xicon 50 Watt Aluminum housed wirewound power resistors.
2. Attach an oscilloscope AND an AC voltmeter across this resistor--you want to measure the AC voltage on the Output transformer secondary
3. Attach a signal to your input of the amp [I use a B&K sine wave function generator--150mV AC [.150V] @ 1000 Hz. I attached a 1/4 plug from an old cable so I can plug it right into any amp I want to.
4. Increase the amp's volume until the sine wave starts to clip [flatten out on the top and bottom of the crests].
5. Measure and record the AC voltage at this point.
6. Square the measured AC voltage. EX: 15VAC Measured--15 X 15 = 225VAC
7. Divide the squared voltage by the resistor value [Ohms]. EX: 225VAC/16Ohms=14.0625 Watts
This is your Watts RMS power output at clipping.
Jason
Plate Dissipation [Watts]=Plate Voltage [Volts] X Plate Current [Amperes]
1. Measure plate voltage [DC]--I like to use the shunt method and/or Randall Aiken's method of measuring voltage drop across the primary and converting to current. See http://www.aikenamps.com/
2. Measure plate current [Amperes]--Make sure you convert Milliamperes to Amperes--divide Milliamperes by 1000 to get Amperes. EX: 20 milliamperes X 1000=.02 Amperes
3. Measure cathode voltage [DC]
4. Subtract the cathode voltage from the plate voltage--don't forget this step if you are biasing any cathode biased amp. EX: 330VDC plate volts - 15VDC cathode voltage = 315VDC effective plate voltage
5. Multiply effective plate voltage by plate current. EX: 315VDC X .020Amperes = 6.3 Watts
That is how much heat your EL-84 plates are dissipating. The maximum heat dissipation EL-84's are designed for is 12 Watts.
Watts RMS at clipping Measurement--do this after you verify the bias:
1. Attach a dummy load [big resistor] to match your Output transformer secondary tap [4,8,or 16 Ohm]. I like the Xicon 50 Watt Aluminum housed wirewound power resistors.
2. Attach an oscilloscope AND an AC voltmeter across this resistor--you want to measure the AC voltage on the Output transformer secondary
3. Attach a signal to your input of the amp [I use a B&K sine wave function generator--150mV AC [.150V] @ 1000 Hz. I attached a 1/4 plug from an old cable so I can plug it right into any amp I want to.
4. Increase the amp's volume until the sine wave starts to clip [flatten out on the top and bottom of the crests].
5. Measure and record the AC voltage at this point.
6. Square the measured AC voltage. EX: 15VAC Measured--15 X 15 = 225VAC
7. Divide the squared voltage by the resistor value [Ohms]. EX: 225VAC/16Ohms=14.0625 Watts
This is your Watts RMS power output at clipping.
Jason
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Jason
Screw up #2
John,
Also, in step #2, don't multiply . Divide milliamperes by 1000 to get Amperes!!
Jason
Must be the 99 degree heat...
Also, in step #2, don't multiply . Divide milliamperes by 1000 to get Amperes!!
Jason
Must be the 99 degree heat...
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