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In Reply to: reducing heater voltage - one resister or two? posted by eedork on March 24, 2007 at 20:40:29:
I'm using this two circuits:Pic. 1
Case 1: If the heater windings have a middle tap.
Case 2: I force symetry.
In both cases I use 2 resistors.
Follow Ups:
In your Case 2, what wattage are the 100 ohm resistors? 1/2 watt?
The formula is N = U * U / R. in the case of 6.3V filament voltage this will give 6.3 * 6.3 / 100 = 0.3969. I always take 1 Watt. In case of 12.6 V it's twice the value, about 0.8W.The reduction of voltage in his example 0.1R and an estimated current of 2.5A will be 0.25 V. So you must align this value for your specific situation. The load then will be 0.25 * 0.25 / 0.1 = 0.625 W. I take some more, because the nominal load of a resistor is defined for a certain temperature (e.g. 50 - 60 °C).
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Long Live Dr.Gizmo
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Long Live Dr.Gizmo
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