Confused

[changes]

well i'm gonna build a tube preamp (2x12AX7) with a toroidal transformer
and i want to run the heaters on DC for the minimum noise possible.
can i use a 12V regulator?will i still have enough ma to run the tube heaters?
if yes will i have to fullwave rectify the 12VAC or just use a diode in series???

[davebungo]

From what I can gather (by searching for "12AX7 heater"), the current draw is 150mA @12.6V.  I assume this to mean 12.6VAC RMS.

[The Tone God]

can i use a 12V regulator?

Yes but take into account that you will need a few extra volts more then the regulator's stated output to feed the regulator. Also be aware of how much current the regulator can supply.

will i still have enough ma to run the tube heaters?

I couldn't tell you as I have no details of what transformer your using or what the current requirements of the tube circuit itself are.

if yes will i have to fullwave rectify the 12VAC or just use a diode in series???

Once again I have no details of your transformer so I couldn't tell you.

Need more information.

Andrew

[Mike Burgundy]

If you have a 12V transformer, 12V DC will be tough at higher currents. You may want to employ a variable regulator (such as an LM317or a 350T - pick one that can handle enough juice) and adjust for a neat 6.3V and hook the filaments up in parallel instead of series. There should be schems in the datasheet at least. If you want good regulation, go for good rectification. I'd say full-wave bridge.
Everything you do loses a bit of power somewhere (regulator datasheet is a good source of information here, plus including some extra margin is a good idea), no idea about the circuit's needs or the transformer's power handling capacity.
hih

[puretube]

well i'm gonna build a tube preamp (2x12AX7) with a toroidal transformer
and i want to run the heaters on DC for the minimum noise possible.
can i use a 12V regulator?will i still have enough ma to run the tube heaters?
if yes will i have to fullwave rectify the 12VAC or just use a diode in series???

reg: yes;
enough mA, when the wallwart can deliver enough for the toroidal plus for the 2x 150mA@12V.
fullwave: yes, lower ripple=less noise=less work for the reg=smaller electrolytics;
if the rectified voltage isn`t more than 15V, you could use a "low drop" reg.
put a heatsink on the reg.!

(I assumed you do the "back-to-back" supply-thingy)
much more info available thru the >search< button.