The power switch on my Audio Research D130 has failed. Now that the new (US$16.72!!) switch has arrived from ARC, I want to make sure that this never happens again. The ARC service representative told me, "...yeah, they arc and then corrode and eventually fail." Apparently, ARC has never tried putting a suppression cap across the power switch to protect it from the primary voltage spike when the switch opens. I want to put one on and I see recommendations here of about 10 nano-Farads, Class X capacitors. My problem is that caps do not receive class X or Y designations in the US. What would an equivalent dielectric type be? Some devices, such as Quencharc, have Underwriters Laboratories listing, but I think that a Quencharc (e.g. 100 nF w/ 150-ohm series resistor) is meant for DC and over-doing it a bit. Should I just grab any 630V ceramic? How high can the voltage spike from a 800W 120V primary go?
WIMA Radio Interference Suppression (RFI) Capacitors Class X2
These are in common use in my part of the world.
Make sure capacitor is continuous AC Rated, rather than DC rated
Regards
These are in common use in my part of the world.
Make sure capacitor is continuous AC Rated, rather than DC rated
Regards
Capacitors used across AC lines are supposed to be flameproof. They aren't supposed to catch fire if they short. I have seen ceramic capacitors used in this application because ceramic doesn't burn. If you have an old computer power supply, you can salvage an X rated capacitor out of it. Some of the power supplies have 3-4 of those X capacitors in the line filter.
Don't put the cap across the switch. Put it across the primary after the switch and any fuse. X-rated caps should be available in most countries. 10nF sounds fine to me.
X caps can be made from several dielectrics. They are usually self-healing film caps, designed to cope with continuous AC stress and almost guaranteed not to fail short-circuit. Y caps are similar, but smaller values, and definitely guaranteed not to fail short-circuit - well, as guaranteed as anything can be.
X caps can be made from several dielectrics. They are usually self-healing film caps, designed to cope with continuous AC stress and almost guaranteed not to fail short-circuit. Y caps are similar, but smaller values, and definitely guaranteed not to fail short-circuit - well, as guaranteed as anything can be.
Line filter will also suppress arcing?
So, you are suggesting that I use this cap as a line filter as well as a suppression cap for that moment when the amp is turned off? I suppose that putting it across the primary winding will serve both purposes, although I hadn't planned to do anything other than protect that over-priced switch.
Sadly, I do not. Further research has revealed that there is an American vendor of X and Y rated caps, Antique Radio Schematics and Capacitors for Tube Radios, but the minimum order is US$20. I will continue searching.
A cap on its own does not do much line filtering, although it might reduce noise a bit. Two reasons for putting it across the primary instead of across the switch:
1. When switched off, a cap across the switch would allow some mains current to flow - at the very least this could create confusion during fault tracing.
2. When switched off, a cap across the switch is exposed to full mains voltage. Assuming that domestic equipment spends more time off than on, this would shorten the cap life. Note that X caps can gradually lose their capacitance value, some more than others, because every mains spike burns away a little bit of film.
1. When switched off, a cap across the switch would allow some mains current to flow - at the very least this could create confusion during fault tracing.
2. When switched off, a cap across the switch is exposed to full mains voltage. Assuming that domestic equipment spends more time off than on, this would shorten the cap life. Note that X caps can gradually lose their capacitance value, some more than others, because every mains spike burns away a little bit of film.
I had a .01 uf 1000 v rated ceramic cap across the power switch of my ST70 amp for 37 years. It was plugged in for 22 years then I put away for lack of US made tubes. Back online in 2011. X or Y designations were not invented in 1970 when I intalled it. I saw caps like this on Howard Sams photofacts, had a problem with turn off pop, and made a deduction which led to installing the cap. No pop at turnoff.
The power switch bridge cap I installed on the dynakit PAS2 preamp was vaporized in about 1985, but the power switch was carbon tracked across in the same event. It was turned off at the time. I came home and found the preamp on with the power switch turned off. I count that event as a surge caused by lightning, as we have a lot of that here, particularly on that day. The switches are small slide switches, nothing with a super sized gap between electrodes.
Don't go lower than 1000 v rating if you go with a ceramic cap. These were US made surplus caps from the R***** S***** grab bags of the late sixties. Modern vendors may have discovered a way to make things cheaper, or simply lie about the 1000 v rating. Buy a name brand ceramic cap, or insist on X2 which is audited by UL/CSA/VDE for a quality control program. Refrigerators/air conditioner shutoff can emphatically produce 600 v spikes on a 120 VAC line.
About the lightning, they now make MOS supressors , to go across the hot and neutral and take the surge. They are blue and have a broken S on them, and a number which is the AC RMS voltage rating. They are also UL/CSA/VDE rated. I salvage them from dead PC power supplies and put them in my amps preamps and mixer. Most of the ones I use are 500 V units from factory Variable Speed Drives. Even a slide switch should be able to hold off 500v.
The power switch bridge cap I installed on the dynakit PAS2 preamp was vaporized in about 1985, but the power switch was carbon tracked across in the same event. It was turned off at the time. I came home and found the preamp on with the power switch turned off. I count that event as a surge caused by lightning, as we have a lot of that here, particularly on that day. The switches are small slide switches, nothing with a super sized gap between electrodes.
Don't go lower than 1000 v rating if you go with a ceramic cap. These were US made surplus caps from the R***** S***** grab bags of the late sixties. Modern vendors may have discovered a way to make things cheaper, or simply lie about the 1000 v rating. Buy a name brand ceramic cap, or insist on X2 which is audited by UL/CSA/VDE for a quality control program. Refrigerators/air conditioner shutoff can emphatically produce 600 v spikes on a 120 VAC line.
About the lightning, they now make MOS supressors , to go across the hot and neutral and take the surge. They are blue and have a broken S on them, and a number which is the AC RMS voltage rating. They are also UL/CSA/VDE rated. I salvage them from dead PC power supplies and put them in my amps preamps and mixer. Most of the ones I use are 500 V units from factory Variable Speed Drives. Even a slide switch should be able to hold off 500v.
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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.
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.
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.
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.
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.
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.
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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Re: This should do it
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.
"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.
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.
So my question is why is AC current not flowing in the DH 200 circuit? I was taught capacitors block DC and pass AC. By looking at the schematic AC should be flowing through the 5nf capacitor. Also the Hafler SE120 uses the same set up and I own both amplifiers. Thanks for any one that can explain this to me. MAH
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