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previous: Major Pain Well after using a hammond power tr... -- 11/12/2003 12:47 AM View Thread

Re: Best way to reduce Filament voltage?

11/12/2003 1:31 AM
Don Symes
Re: Best way to reduce Filament voltage?
First - filament voltages are spec'd +/-20% (iirc), whch goes ofer 7.5V. Even 6.3*1.1 = 6.9V.  
Yes, you will slightly shorten your tube's life, but not by an amount you're likely to notice.  
Next - the resistors method is cheap and reliable provided you add up all the heater currents - they're parallel, right? - and do a bit of algebra to get the resistor values and wattages, then use the nearsest standard value and the next bigger wattage for reliability.  
You want two resistors to drop .7V.  
Each one needs to drop .35V  
0.35V/HeaterCurrent = ResistorValue  
HeaterCurrent^2 * ResistorValue = Wattage  

Matt H also, measure the filament winding ... -- 11/12/2003 2:23 AM
Major Pain Don,Would this be adding a resi... -- 11/14/2003 3:43 PM