[AMRadio] Solid State 575 mercury vapor RectifierReplacementsneeded


Brett Gazdzinski Brett.Gazdzinski at verizon.net
Sun Oct 4 18:24:35 EDT 2009


They also make 1000v 3 amp diodes, I got a bunch on line once, quite cheap.
That is a lot of current....

Brett

----- Original Message ----- 
From: <sbjohnston at aol.com>
To: <amradio at mailman.qth.net>
Sent: Sunday, October 04, 2009 4:22 PM
Subject: Re: [AMRadio] Solid State 575 mercury vapor 
RectifierReplacementsneeded


> >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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