[AMRadio] Solid State 575 mercury vapor RectifierReplacementsneeded


Bernie Doran qedconsultants at embarqmail.com
Sun Oct 4 10:31:52 EDT 2009


Hi Steve: I have used the 4007s many times. My understanding is that they no 
longer require the equalizing resisters and caps across them as the reverse 
current is similar to avalanche diodes,    they are so cheap now that you 
can just stack 20 of those rascals.  some one needs to check that. also if 
one is concerned about forward current and needs more than one amp, it is 
very easy, just build two stacks and add a little resistance in series with 
each stack before connecting them in parallel. the resistance nearly 
balances the load between each stack as the drop across the resistor is much 
more than the drop across the diodes.  ten Ohms should work fine.     Bernie 
W8RPW---- Original Message ----- 
From: <sbjohnston at aol.com>
To: <amradio at mailman.qth.net>
Sent: Sunday, October 04, 2009 10:04 AM
Subject: Re: [AMRadio] Solid State 575 mercury vapor 
RectifierReplacementsneeded


> 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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