[AMRadio] Solid State 575 mercury vapor Rectifier Replacementsneeded

[sbjohnston at aol.com]

I've made my own solid-state plug-in replacement rectifiers for a 
variety of tube types.  I look up the tube specs and select solid-state 
diodes that stack up appropriately for current and forward and reverse 
voltages. I usually end up using either 1N4007s or 1N5408s.  From 
on-lline sources like Digikey or Mouser or All Electronics the diodes 
are very inexpensive, ten cents to maybe 30 cents each.

I put the diodes on a rectangular piece of perfboard sized to fit 
upright with its bottom end tucked within the sides of the base of the 
defunct tube it is replacing.  A small L bracket holds it in place.

If you use diodes from the same "run" (which is easy if they are sold 
on the paper tapes used by manufacturers today) then I find no 
equalizing components are needed.  I add a few more diodes than the 
calculated voltage required for an extra measure of safety and have 
never had a failure, even in broadcast rigs on the air 24/7 with lots 
of lightning and power bumps to deal with.

You can expect somewhat higher voltage from the new stack than the 
original tube rectifier - if that is a problem for the rig, then add a 
series power resistor to simulate the internal voltage drop of the 
earlier tube.  So far I've only needed to do that once when the new 
higher B+ exceeded the rating of the by-pass caps in the other sections 
of the rig.  Otherwise the rigs seemed to thrive on the higher voltage.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
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