[Amps] 1N Diodes

[jim.thom jim.thom@telus.net]

Date: Thu, 1 Jul 2021 08:08:40 +0800
From: Alek Petkovic <vk6apk at bigpond.com>
To: amps at contesting.com
Subject: Re: [Amps] 1N Diodes


<NO!. Leave the higher voltage rated diode/s in there. Don't go backwards
<and risk it failng again.

<As Lou said, be safe and stick 1N5408s in there. They do NOT affect any
<thing else in the amp. They just have a much higher rating and safety
<factor.

<73, Alek, VK6APK

## The safety diode is wired  directly between the B- of the HV filter cap
assy...to the chassis, that's it, done.   IF the  B+ arcs from anode to
grid, or  to the chassis, 1000-5000 vdc of  B+ is more than ample to turn
on the diode,  regardless of its  PIV rating voltage.   The diode will
start to conduct with just .5 vdc..and you have way the heck more than
that,  you have the full B+ !.   Fault path is from  B+  to  grid /
chassis..then along the chassis, up from the chassis onto the positive (
un-banded) end of the safety diode...then back to the B-  of the HV filter
cap assy...completing the loop.    Then either the B+ fuse open up, or the
mains breakers open off.   A  25-50 ohm resistor should be used in the B+
lead, to limit the fault current to a safe value.  IF a HV fuse is used,
the fuse should be  prior to the 25-50 ohm glitch resistor assy.

##  Forget the  1N4001, or  1N4007  junk, they only have like a 30 amp
surge rating.  The  1N5408 has a 200 amp surge rating..and the  6A10 /
PM-600  series of diodes have a 400 amp  surge rating.  The  10AO8 has a
600 amp surge rating.   I typ will use 2-4 x 6A10's in parallel, all
pointed in the same direction, to make one big diode.  Then I end up with a
800-1600 amp surge rated  safety diode assy.  Then u can cro-bar the B+
till hell freezes over, and they will never fail.

##  The puny  1N4002 and  1N4007 with it's  30 amp surge rating is too
small for a safety diode. ( u would have to parallel 7 of em to equal a
single 1N5408).  With no glitch resistor used, there is nothing to limit
the fault current.  Even a 2500 vdc supply + a 25 /  50 ohm glitch resistor
will result in  100 / 50 amp fault current.
When the 1N4002/007 diode fails, it will fail shorted.  With the diode
shorted, your B- is now bonded to the chassis...via the shorted diode...and
your grid + plate current can't be measured.

##  Just use the right diode to begin with..and that's not the 1N400X
series.

Jim   VE7RF