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Old 13th December 2012, 06:17 PM   #11
AndrewT is online now AndrewT  Scotland
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You must use an appropriately rated capacitor.
For mains use that requires you to use either X or Y rated capacitors.
They are generally available and you should be able to find retailers easily. Go and look.

And search out some literature on X & Y capacitors.

A cap across the primary is a good idea.

A snubber across the switch is also good. The snubber is an integrated mains capacitor and resistor, series connected, inside the two (2) lead device.
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Old 13th December 2012, 06:18 PM   #12
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Default HAFLER DH-200

In the Hafler DH-200, it's a 5nF/1000V across the switch (C14). You can use a 4n7 or 10nF Type X or X2 (250Vac).
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File Type: gif HAFLER DH200 SW.gif (5.2 KB, 53 views)
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Old 13th December 2012, 06:23 PM   #13
AndrewT is online now AndrewT  Scotland
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Michael,
do you know which pole of the mains plug is Live?
It seems odd that Haffler have the fuse in one pole and the switch in the other pole. I consider that bad practice.

But then I'm used to UK regulations that require both poles to be switched.
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Old 13th December 2012, 06:58 PM   #14
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Default I think this should do it

VY2103M63Y5UG63V0 Vishay/BC Components | Mouser
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Old 13th December 2012, 07:00 PM   #15
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Andrew,

I don't really know. Some of these vintage amps are only 2-pins.

The only reason I can think of for the Fuse to be on the other side of the transformer is so that it doesn't blow due to current inrush. That is on condition that the switch side is Live. I could be wrong.

My preference is to have the Fuse on the Live end followed by Switch. I feel it's safer this way. Once the fuse blows, Mains is disconected. I think UK uses a DP switch for extra safety, one on the Live and the other on the Neutral. Perhaps this extra safety is due to a higher (read lethal) 240V Mains.
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Old 13th December 2012, 07:11 PM   #16
DF96 is offline DF96  England
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The same current exists in the switch and the fuse, however they are wired. However, the fuse should ideally be in the Live side so that it isolates the circuit when it blows. The switch should also be in the Live side or both.

Yes, fuse first then switch - in case the switch develops a short. If you look inside a switch you may be surprised at how thin the insulation can be.

120V mains can be lethal too.
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Old 13th December 2012, 07:16 PM   #17
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by GOR3 View Post
yes it is X rated.
But it does not follow the standard markings ! X440 is in the item description.
It should be X1 or X2, indicating the standard it meets for a mains rated capacitor.
X1 300Vac is plenty OK for both 110/120Vac and 220/240Vac operation.

Edit:
trying to read the marking in the cap pic. Looks like it might say X1 440~
That would indicate it is suitable for UK three phase, where across two phases we have 400/440Vac.
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Last edited by AndrewT; 13th December 2012 at 07:19 PM.
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Old 13th December 2012, 08:27 PM   #18
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Default Re: This should do it

Quote:
Originally Posted by GOR3 View Post
Yes, I see the variety available now. What discouraged me at first was that Newark Electronics makes it hard to find X and Y rated caps (or even UL 1414). Mouser, Allied and Digi-Key make it much easier (for me) to find them.
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Old 13th December 2012, 09:56 PM   #19
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"About the lightning, they now make MOS supressors"

We used GE metal oxide varistors (MOV) in our DC motor drive controls because of the transients the motors created. If you use a MOS supressor, keep in mind they fail as a short so be sure they are behind the fuse. I put one across the transformer primary of my Dynaco Stereo 400 to cure a nasty turn off thump. They have to be properly sized for the application.
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