[Amps] Shunt resistors for a bridge made of 6A10 diodes in

[Jim Thomson]

Date: Wed, 27 Jan 2016 20:31:48 +0800
From: "Steve Ireland" <vk6vz at arach.net.au>
To: <amps at contesting.com>
Subject: [Amps] Shunt resistors for a bridge made of 6A10 diodes in
Alpha 91b

G?day

I am refurbishing the power supply board in my Alpha 91b and am going to replace the KD202P diodes which make up the bridge with 6A10 diodes (1000V 6A and only A$1.95 each). 

The original bridge had strings of five KD202P a side, with shunt resistors across each diode of 500K 1W. The stud mounted diodes are looking pretty burnt around the retaining washers/bolts, so it is definitely time (and I have a strange earth leakage fault).

Please, I?d really appreciate some advice about what value of shunt resistor to use on each of the twenty 6A10 that will make up the bridge?

PS The replacement encapsulated bridge rectifier sold by Alpha/RKR designs (5kV, 2A) is US$150, so this the reason for looking for a cheaper solution.

Vy 73

Steve, VK6VZ     

##  Dont put  ANY  shunt resistors  across a 6A10.  They don’t need them!   It’s a series circuit, and the current through each leg of 5 diodes
will be identical..whether frwd biased or not.  Shunt resistors to equalize something that is already equalized went the way of the do-do bird years ago. 
I have been using 6A10 diodes for a long time now.  They don’t requite any shunt components..and that includes stuff like .01 uf disc ceramic caps.  You might want to use
6 diodes per leg,  if they will fit.   The wire leads out each end of the 6A10 ....IS the heat sink for them, so leave em on the long side if possible.   They are typ 1250-1400
piv  when you test them.  The 6A10 is a superb diode. I use it for everything from B+ supplies to safety diodes, and also strings of them  for bias on GG amps. 

Jim   VE7RF