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20th Apr 2006, 11:25 pm | #1 |
Moderator
Join Date: Feb 2006
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Replacing selenium bridge rectifiers.
What is the requirement when replacing selenium bridge rectifiers? Can you just replace the rectifier with a silicon bridge rectifier or do you have to use a series resistor to mimic the forward voltage drop?
Any advice would be extremely welcome. The equipment I'm working on is a Tandberg 74 stereo tape recorder. The mains bridge rectifier has gone S/C on one leg. |
20th Apr 2006, 11:29 pm | #2 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,853
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Re: Replacing selenium bridge rectifiers.
I'd do the latter, i.e. use a series R, chosen so that the HT voltage is as close to the specified value as you can get it
PS Keep up the good work with your new magazine |
20th Apr 2006, 11:35 pm | #3 |
Retired Dormant Member
Join Date: Apr 2005
Location: Reading, Berkshire, UK.
Posts: 95
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Re: Replacing selenium bridge rectifiers.
I'm with Nick on this one. In my past I have always included a small value resistor. Mainly to reduce the surge current.
Don't ask me why. The last one I did was well over 20 years ago. |
21st Apr 2006, 12:10 am | #4 |
Moderator
Join Date: Jun 2003
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Re: Replacing selenium bridge rectifiers.
I'd also agree, but there is actually some dispute about the necessity of adding a series resistor. Some people argue that you don't need it for current limiting purposes, and so long as the HT voltage is within limits you can just replace the selenium bridge with silicon. I always add a 200 ohm resistor though - the cost is minimal and I'm sure it's kinder on the smoothing electrolytics and other components. It reduces the peak load on the bridge, and also seems to make the HT voltage 'more or less' right.
Best regards, Paul |
21st Apr 2006, 12:44 am | #5 |
Hexode
Join Date: May 2005
Location: Wigan, Greater Manchester, UK.
Posts: 479
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Re: Replacing selenium bridge rectifiers.
Not exactly a bridge rectifier but, I remember in the early 1960s, I replaced the infamous Mazda U801 valve on an Ekco tv with a BY100 silicon rectifier and was advised to place a 25 ohm 10w w/w resistor in series with it, this I did, the increase in brightness and contrast on the screen was phenomenal and nothing overheated.
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21st Apr 2006, 8:36 am | #6 |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: Replacing selenium bridge rectifiers.
In the far distant past, when the then new BY100 appeared to solve the world's problems, or at least the smell of sewage from a failing selenium reccy, it arrived as a kit from Radiospares with a 5w 10 (?) ohm wirewound.
U801, eh? Almost nice enough to put on your mantelpiece!
__________________
Mike. |
5th Jun 2006, 9:28 pm | #7 |
Retired Dormant Member
Join Date: Feb 2005
Location: Monmouthshire,on South Wales border
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Re: Replacing selenium bridge rectifiers.
I would alays add a resistor to limit the surge current,this is important.Also often necessary is a small value cap across each diode,otherwise the spikes create modulation hum.
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