DC heater FC-1 circuit

[johnsonad]

I'm considering using a DC heater supply in my upcoming SR45 build in hopes to get the hum as low as possible as they will be used with very sensitive headphones.  This posted circuit is PJ's which I found in AA.  I intend to use an EML 45 with a posted heater draw of 2.5v/5% tolerance/1.5 amp draw. 

I'm a little fuzzy on the voltage drop of this circuit and could use a little help. Also, if you happen to have a transformer recommendation, please post it.  Space will not be an issue, just hum and noise.

Thanks,

Aaron

 

[Paul Joppa]

Use a 6.3vCT winding, and a fullwave CT rectifier (two diodes, not 4). Start with a 1.67 ohm resistor rated 10 watts or more (I'd use six 10-ohm 2-watt or greater, in parallel, since those are readily available.) in place of the filament - you don't want to fry those expensive tubes until you are sure the voltage is right! The FC-1 can be wired two ways, for 2.5 amps or 1.25 amps. The 1.25 should work at 1.5 amps; try it both ways to adjust the voltage (the 1.25 amp 2wiring produces less output voltage than the 2.5 amp setup)

If neither one produces the target voltage, post again and we'll analyze the problem.

 

[johnsonad]

Thanks Paul, I'll post results once it's up and tested.