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Unlike a modern silicon diode, which drops 0.7 volts across itself when conducting, a selenium-stack typically drops a bit more, similar to a vacuum tube, so the "diode check" function on modern DMM's is useless here. If they work, leave 'em alone. If you do replace them, you can use the DMM to trim the series resistors to exactly the value needed to get the proper B+ voltage.
As for aesthetics, I look long and hard in junker chassis', swap meets and ePay to avoid those cheesy-looking ceramic resistors we shamefully import these days. An IRC ceramic or Ohmite "Brown Devil" looks so sweet and close-to or actually period-correct as well!
Now here's a question for all those who rave about modern low-ESR electrolytics:
Does the lack of this "effective series" resistive component actually result in a greater surge current at turn-on? Were the 1940's originals low-ESR as well when new? It would seem to me that this scenario, IF that is correct, would stress the aged selenium device even more...
Last edited by Einar72; 03-07-2012 at 04:18 PM.
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