here what jb says about that.
Note the three 47µF 450V capacitors, which might seem small in value compared to values used in solid-state rectified power supplies. Large values are a bad idea, however, when it comes to tube rectifiers. Why? The tube rectifier cathode cannot handle the high current spikes that a large capacitors force through rectifier's cathode. Most tube rectifier specifications state a maximum capacitor value of 50µF or 60µF, so the 47µF plays it a bit safe. In addition, the two capacitors after the RC resistor add an additional 94µF to the total capacitance. The two 100-ohm resistors at the rectifier's anodes also limit the peak surge current through the rectifier. For those who can never get enough iron, jumper J7 can be replaced by an optional external choke.
Note the three 47µF 450V capacitors, which might seem small in value compared to values used in solid-state rectified power supplies. Large values are a bad idea, however, when it comes to tube rectifiers. Why? The tube rectifier cathode cannot handle the high current spikes that a large capacitors force through rectifier's cathode. Most tube rectifier specifications state a maximum capacitor value of 50µF or 60µF, so the 47µF plays it a bit safe. In addition, the two capacitors after the RC resistor add an additional 94µF to the total capacitance. The two 100-ohm resistors at the rectifier's anodes also limit the peak surge current through the rectifier. For those who can never get enough iron, jumper J7 can be replaced by an optional external choke.
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