[Amps] Shunt resistors for a bridge made of 6A10 diodes in Alpha 91b

[Steve Ireland]

Hi Hardy

Good to hear from you.  Thanks for the great advice.  After 20 years of 
hard, hot work, there is heat-related oxidisation over just about every 
joint/connection on the 91b power supply board. I'll be resoldering all the 
joints.

Vy 73

Steve, VK6VZ

-----Original Message----- 
From: Hardy Landskov
Sent: Friday, January 29, 2016 1:26 AM
To: 'Steve Ireland' ; amps at contesting.com
Subject: RE: [Amps] Shunt resistors for a bridge made of 6A10 diodes in 
Alpha 91b

Steve,
I don't think shunt resistors are needed anymore with today's close 
manufacturing processes. Someone may have a different opinion.

Also, check the leads that supply the filament current. They go through 
crimp connectors on the top of one of the pc boards. Mine developed an 
oxidation which burned up the insulators on the crimp connectors. I replaced 
the connectors and soldered the connectors and no problems since.
73 Hardy N7RT


-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Steve Ireland
Sent: Wednesday, January 27, 2016 11:32 AM
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

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