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Old 8th Oct 2011, 9:09 pm   #1
Ken
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Default Goblin time spot power supply

This radio has two large mica 0.01 microF mica caps wired in series across the primary of the mains transformer marked C12 and C13 on the attached part of the circuit diagram. For safety reasons I thought I would replace them. As this seems to put 0.005 microF across the mains I thought I should use X2 types. However, the connecting point between the caps is connected to earth and so one is connected L to E and the other N to E and I then wondered if I should be using Y2 types. I suspect the correct type to use here is the X2 type but I would just like to confirm this. I am also wondering how critical the values are here. I do not have any 0.01 but I do have 0.033. Will 0.033 do here? The voltage ratings seem a bit confusing as they are marked 250V AC on one side and 275V AC on the other. They are made by "RIFA". I seem to remember reading that this type of cap can fail in a spectacular way. Has anybody had a bad experience with this make?

Regards,

Ken.
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Old 8th Oct 2011, 10:19 pm   #2
Herald1360
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Default Re: Goblin time spot power supply

If the capacitors are L & N to ground, they should be Y type. Only L-N with no ground connection is X type. I find it helpful to think of a pair of overhead lines for Line and Neutral, X goes across the lines and two Y caps in series across the lines with their centre point sagging a bit and connected to the ground underneath look like a Y. (That's the way my mind works, anyway).

The different voltage ratings on your X types will likely be different national standards requirements, though it's possible (read the markings carefully or consult the data sheet) that they may be X rated at 275V and Y rated at 250V.
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Old 8th Oct 2011, 11:35 pm   #3
kalee20
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Default Re: Goblin time spot power supply

Quote:
Originally Posted by Ken View Post
They are made by "RIFA". I seem to remember reading that this type of cap can fail in a spectacular way. Has anybody had a bad experience with this make?
Yes - the epoxy-encapsulated, transparent types, are prone (ie almost certain) to cracking and letting moisture in. Avoid them like the plague!

Other, thermoplastic-cased RIFA types seem fine.
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Old 9th Oct 2011, 10:40 am   #4
Ken
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Default Re: Goblin time spot power supply

Thanks for the replies. I don't have any Y2 types but had a quick look at an old Maplin catalogue (2007) and they had them then. I'll try during the coming week to see if they still have them.
Quote:
Yes - the epoxy-encapsulated, transparent types, are prone (ie almost certain) to cracking and letting moisture in. Avoid them like the plague!
These are exactly the type I was thinking of using. I also have some 0.1 microF from the same maker but these are encapsulated in a blue plastic. If I can I'll try to buy another make when I go for the Y2s.

Thanks for your help,

Ken.
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