[AMRadio] Solid State 575 mercury vapor RectifierReplacementsneeded

Sun Oct 4 16:22:42 EDT 2009

>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.

Yep, that's been my experience too.  I prefer to use diodes that are 
all from the same "run", at least bought at the same time, so that the 
diodes are similar to one another.  But that precaution may not be 
necessary.

>If one ... 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.

Excellent point about putting strings of solid state diodes in parallel 
for higher current capacity.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
---------------------------------------------------------
Radio is your best entertainment value.
---------------------------------------------------------

-----Original Message-----
From: Bernie Doran <qedconsultants at embarqmail.com>
To: Discussion of AM Radio in the Amateur Service 
<amradio at mailman.qth.net>
Sent: Sun, Oct 4, 2009 9:31 am
Subject: Re: [AMRadio] Solid State 575 mercury vapor 
RectifierReplacementsneeded

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/
> ---------------------------------------------------------
> Radio is your best entertainment value.
> ---------------------------------------------------------
>
>
>
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