| IIRC from way back, when I was but a youngster and silicon rectifiers were also
new, the replacement of Se by Si rectifiers was often discussed. The advice was
to add a resistor to limit inrush current to the filter capacitors, since Se
rectifiers have a non-linear forward characteristic. In effect, they limited
current to (mumble). The old electrolytics could easily handle the Se's inrush,
but were overstressed by the large inrush current from the Si's.
The early
Silicon rectifiers were, themselves, vulnerable to the high current demand of a
discharged capacitor, so both needed protection. Modern diodes are much better
in that respect
The preventative for blown electrolytics was about 4.7 to 22
ohms in series with the Si rectifier.
If there are electrolytics in the
circuit, they may well be ancient and ready to blow anyway; if they've already
been replaced by more modern varieties or better, they may be more immune (Ha!
thought I was gonna say 'resistant', didn't you!) to high inrush
current.
<Digging deep> A choke-input filter didn't need the resistor
— the inductance did the job.
The concensus was that a 1 or 2-watt
wirewound resistor would be the best general choice in a common 150-volt or so
application. Its wee bit of inductance helped, on top of its robustness
vs the carbon resistors of the day..
Take my ancient recollection with
a suitable amount of salt (and any other seasonings of choice). I now get to
replce the cobwebs around that memory... ---
--Bill. NAL: question the
answers, especially mine. [ Reply to This | Parent | # ]
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