5v to 2.5v for 2a3 filament
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 12th February 2010, 04:47 PM #1 gasser-dude   diyAudio Member   Join Date: Nov 2009 5v to 2.5v for 2a3 filament What would be the best(simple) way if possible to drop 5vac 3amp to 2.5v at 2.5a for heaters for a single 2a3 tube??? Sorry for the dumb ? Hope someone has a simple answer. Thanks in advance.
 12th February 2010, 05:15 PM #2 Arnulf   diyAudio Member   Join Date: Feb 2009 An additional transformer or altered existing winding. All other solutions will waste power or potentially cause noise.
 12th February 2010, 11:09 PM #3 pauldune   diyAudio Member     Join Date: Oct 2009 Location: Netherlands Arnulf is right. However, you could rectify it, and put a 2.5A CCS behind it. Causes a lot of heat in the ccs though...
 12th February 2010, 11:45 PM #4 7n7is Banned   Join Date: Mar 2006 Location: VA Ohms law -> V = IR R = V/I 2.5/2.5 = 1 ohm The heater has a resistance of 1 ohm with 2.5 V across it and 2.5 amps of current going through it. A dropping resistor will have the same current going through it and must have a voltage across it of 2.5 volts (2.5 + 2.5 = 5). Use a 1 ohm dropping resistor. Also see Voltage divider - Wikipedia, the free encyclopedia
 13th February 2010, 02:58 AM #5 jrenkin   diyAudio Member   Join Date: Nov 2007 Location: Denver, Colorado Could you drop with an RC filter and eliminate some of the noise the other guys are commenting on?
Arnulf
diyAudio Member

Join Date: Feb 2009
Quote:
 Originally Posted by jrenkin Could you drop with an RC filter and eliminate some of the noise the other guys are commenting on?
If "R" part is doing the dropping it will heat up (inclusion of a capacitor doesn't affect that), as mentioned above. An alternative would be capacitive dropper, 2600 uF in series with the filament for 1R @ 60 Hz (mains frequency in the US). The problem is finding 2600 uF non-polarized capacitor, but one could substitute two larger capacitors in series (inverse) instead.

This might actually be the best solution as - just like transformer - it doesn't waste power in the form of heat, and on top of everything it also doesn't cost nearly as much or weigh as much as a suitable transformer.

 13th February 2010, 09:01 AM #7 hkoetz   diyAudio Member     Join Date: May 2003 Location: Arnhem 5v to 2.5v for 2a3 filament 2 2A3's is series? __________________ Lateral is best!
pauldune
diyAudio Member

Join Date: Oct 2009
Location: Netherlands
Quote:
 Originally Posted by hkoetz 2 2A3's is series?
remember: filament=cathode!

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