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Tuesday, September 19, 2017
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 Calculate Dropping Resistor for Tube filament


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What to do if the transformer delivers a higher heater voltage as required?

Use a resistor to reduce the voltage you need.
In fact you create a voltage divider...
The dropping resistor is the first and the Tube - Heater the second resistor of this divider.



 
New Tube filament voltage :  Volts *  
New Tube filament current:  Ampere *  
Transformer voltage:  Volts *  
* Required values  

 
 
 
Dropping Resistor:  Ohms  
Voltage dropped by Resistor:  Volts  
Power dissipated by resistor:  Watt  
 
Recommended Resistor power rating:  Watt  
 


 Heater Values of some Power Tubes

Tube Vh Ih

EL34 / 6CA7 6.3 1.5
EL84 / 6BQ5 6.3 0.76
KT66 6.3 1.27
KT77 6.3 1.4
KT88 / 6550 6.3 1.6
211 10.0 3.25
2A3 2.5 2.5
300B 5.0 1.2
5998 6.3 2.4
6AS7 6.3 2.5
6HB5 6.3 1.5
6L6 6.3 0.9
6V6 6.3 0.45
7027 6.3 0.9
7189 6.3 0.76
7558 6.3 0.8
7591 6.3 0.8
801 7.5 1.25
805 10.0 3.25
807 6.3 0.9
811A 6.3 4.0
845 10.0 3.25



Heater / Filament Supplies extern Link

Preamplifier Tube Data