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@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@contesting.com] On Behalf Of Steve Ireland
Sent: Wednesday, January 27, 2016 11:32 AM
To: amps@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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