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reducing heater voltage - one resister or two?

Posted by eedork (A) on March 24, 2007 at 20:40:29

I just finished putting the RH Designs SEP EL84 amp. It works and sounds very good, except for some 120 Hz hum which I think is due to a loose power supply (Eli, etc. you were right - if I regulated my screens this wouldn't be a problem). I had to make a few compromises given the parts at hand - I'm going to rebuild the power supply and make it a little stiffer sometime this week. My power supply is especially weak, as I had to use a CRC filter instead of a CLC, and my B+ is around 270VDC instead of the designed 300VDC. I've thought about replacing the 6CA4/EZ81 I'm currently using with diodes (should gain another 30V), but haven't decided if I want to go that route yet.

In any event, the heater voltage that I am measuring is ~7VAC which is too high. I'd like to step this down to the rating of 6.3VAC and am interested to know if I should use two equal value dropping resistors in either leg of the heater winding, or if a single resistor in one leg will work. The reason I ask is because I already have the parts necessary to put a single resistor in one leg (I need ~.24ohms, and I have two .47ohm resistors in my junk box). I'd rather not have to place an order for one resistor.

Thanks,
-Matt

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