by Geek » Mon May 19, 2008 4:47 pm
Hi,
Assuming you're using a C-L-C filter....
First cap is determined by your rectifier. If you're using a tube rectifier, it will be 10, 22 or 47uF maximum, depending on the tube. If you use a solid state rectifier, 47 or 100uF is OK. Don't forget to bridge SS diodes with a disc cap to keep the fuzz out.
The choke minimum value can be determined by this rule of thumb:
L (henries) = Volts output / current draw in mA
So if you want 350V and let's say the whole thing draws 10mA for four 12AX7 stages (two tubes) + bleeder, that's 350/10 = 35H. Hammond 157G is close enough.
Last capacitor can be another 47uF.
Or you could overshoot the rectified voltage by 50 to 100V with a different transformer and use a C-R-C filter.
Lastly, a regulated supply can be chosen. Probably the best bet here for a preamp.
Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.