The AM Forum

Would appreciate either the specifications or a recommended replacement for a pair of Selenium Rectifiers used in the high voltage power supply section of the Heathkit Model SB-610 Monitor Scope. Subject items are Heathkit p/n 57-44. A check of a cross reference listing for replacement Heathkit parts lists the generic p/n as P3340HQ with no recommended alternates. The original failure was associated with a shorted capacitor, after which all were replaced and IN5408's used to replace the original seleniums and everything functioned normally. However; in the last month's I've incurred Two failures of the IN5408 in the D6 location when running extended periods of operation. Without know ing the specifications for the original, not sure whether My selected replacement is adequate. Additionally the use of these type to replace the Seleniums is the problem of the associated circuitry or maybe there is a quality problem with My replacements. Whatever; would appreciate the original's specs and Recommendations. Thanks

http://www.ohio.edu/people/postr/bapix/SB610.htm

This fellow dealt with the same problem.

His approach is the same as my thoughts, that you need to use several diodes in series to replace each selenium diode.   a 1n5408 has a PIV of 1000 volts.  He used four diodes, with a guessed safety margin.

Check and consider replacing your filter caps and equalizing resistors.