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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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15th Jan 2019, 7:26 pm | #1 |
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Safety Capacitors X or Y or ?
I was looking for assistance in determining the type of capacitor to use for this project.
background: I am currently working a German Simonetta from the 50’s it was sold by a company called Quelle (a mail catalogue company) little information is available about this radio other than it is very similar to the Maestro Luxussuper W816 manufactured by Südfunk. The circuit diagram for the maestro (or what can be read of it ) looks to be very similar (but not identical in places). The radio is actually working with good audio, there is a slight hum noticeable but only when not tuned to a station or the volume turned right down but after checking all the valves I have discovered that the rectifier valve (EZ80) displays 75% (green) on pin 7 but only 25% (red) on pin 1 so I will be replacing this (despite the DC being more or less at the require level as stated in the info) also I may replace the Magic Eye (EM80) it is working but extremely dim. The smoothing cap is a 50μf+50μf however after disconnecting and testing they are more of 26μf+24μf and one has leakage of over 2ma and wont go down despite trying to reform it so that/they will also be replaced. Most of the caps used are WIMA the type that look like licorice sweets The radio is powered by a twin lead mains cable (I plan to change this to a 3 core and attach E to chassis, both L and N go to the on/off switch then up to the transformer ( there is Fuse in the path of L before going to the voltage selector tab at this point there are 2 5000pf capacitors rated 1000V-,600V~,250? (not sure what is after the 250 thus ?) one connects L to chassis and the other connects N to Chassis. (i have attached a photo) so my question is what do I replace them with? I don’t have much experience with safety (X.Y) caps my limited knowledge comes from a article I read a while back that stated X are used between line (L-N) and Y is used from N to chassis so any advice would be appreciated in respect to type brand etc. Many Thanks Darius |
15th Jan 2019, 8:00 pm | #2 |
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Re: Safety Capacitors X or Y or ?
Also, you use class Ys if it's safety critical if the cap fails short circuit. A class Y should always, always fail open circuit.
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15th Jan 2019, 8:17 pm | #3 |
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Re: Safety Capacitors X or Y or ?
You can probably just leave them out, I doubt there'll be much discernible difference.
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Al |
15th Jan 2019, 8:23 pm | #4 |
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Re: Safety Capacitors X or Y or ?
As you are changing the mains cable I would remove these two old capacitors, and put in a single X rated capacitor (around 5nF) from L to N on the radio side of the switch. This will do for the switch what they did for the switch. What they did for the chassis is now being done by the mains cable.
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15th Jan 2019, 8:54 pm | #5 |
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Re: Safety Capacitors X or Y or ?
Class X capacitors can fail short-circuit (as long as there is a fuse upstream). Their "superpower" compared to generic parts is that in the event of an overvoltage spike, the dielectric material will self-heal, at the expense of a few nF of capacitance. A Class X capacitor would be connected between line and neutral. They exist in values up to 1µF
Class Y capacitors have as their "superpower" never to fail short-circuit. They should be used whenever a leaking capacitor would expose any user-accessible external metalwork to dangerous voltages. Class Y capacitors would be connected between line or neutral and earth. To avoid nuisance tripping of RCDs, class Y capacitors only exist in values up to 47nF. All you really need to remember is: X is a cross (across)! As for values, start with 100nF class X and a pair of 4.7nF class Y capacitors. Any reputable brand will do except Rifa! We used to use BC Components (formerly Mullard) in the factory -- I think they are Vishay now.
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If I have seen further than others, it is because I was standing on a pile of failed experiments. Last edited by julie_m; 15th Jan 2019 at 9:00 pm. |
17th Jan 2019, 1:01 pm | #6 |
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Re: Safety Capacitors X or Y or ?
Many thanks for all the answers , one other question in regards these two capacitor in their current configuration comes to mind, are they in anyway assisting in reducing any pickup from the mains?
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17th Jan 2019, 9:48 pm | #7 |
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Re: Safety Capacitors X or Y or ?
I think those Wima capacitors are the least of the worries with that arrangement in the photo. You could replace them though.
It is not wonderful to have that tag board arrangement with Live on it exposed like that, especially for working on the receiver.(unless that area has a cover that was removed before the photo was taken) A number of things could go wrong: You, or someone who inherits it brush their hand against it accidentally working on the set. Or you are working on that with test leads and probes and a dangling scope or generator earth lead touches the live etc etc. The day might be saved by a breaker box RCD, if there is one & it is working, but you cannot guarantee that. It is just a bit crazy to have live exposed in that position. A really simple fix, while leaving it standard, is to get a flexible sheet of insulating material, even a sheet of clear mylar would work with four holes punched in it . Undo the fixing screws for the tag board and wrap the sheet around it and pass the screws back through the pairs of holes and re-mount the board with the insulation now over it, some spacers +/- longer screws might be needed. So you don't modify the design, just retain some insulation over those tags. It will be much safer to work on. If you use clear mylar then you can still see it all. |
18th Jan 2019, 3:51 am | #8 |
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Re: Safety Capacitors X or Y or ?
I wouldn't call capacitors that are 100% guaranteed to be leaky or even shorted, the least worry. Live connections within the set, though, aren't really considered problematic as anyone opening up the set would (or should) know. Often, there's a warning on the back as well. Non-flameproof insulation sheets might be considered problematic, especially when the capacitors wouldn't be replaced.
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18th Jan 2019, 5:19 am | #9 |
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Re: Safety Capacitors X or Y or ?
Its hard to find any insulation that is completely flame proof (except for asbestos), even that phenolic board already there could burn. Its still better to have the extra insulation to avoid a shock hazard. Thin fibreglass sheet is not bad if you want to keep the fire Marshal happy and those old Wima caps may well be better than new Rifas.
Last edited by Argus25; 18th Jan 2019 at 5:24 am. |
18th Jan 2019, 11:50 am | #10 | |
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Re: Safety Capacitors X or Y or ?
Quote:
Those on your set look in good physical condition and aren't, for example, waxed paper caps as found on say the Bush DAC90A which have a propensity to go off with a bang. The phenolic voltage selector board and associated wiring on your set looks in good condition too, with no signs of carbonisation. If you did feel inclined to change the caps, nowadays they'd be 4,700 pF (4N7/.0047) rather than 5,000. These from Farnell would be suitable: https://cpc.farnell.com/vishay-bc-co...047/dp/CA06289 (You'll see the spec at that link). Hope that helps a bit. Good luck with the restoration Darius.
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18th Jan 2019, 12:39 pm | #11 | |
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Re: Safety Capacitors X or Y or ?
Quote:
Adding random pieces of insulation doesn't make a set substantially safer to work on anyway since you would have to insulate everything including the transformer and the mains switch (which is probably easy to touch if you happen to reach under the chassis. And then you still get shocked by the HT) and you would need more than a bit of plastic sheet, since you can reach under plastic or have a sharp piece of wire push through. Even modern mains fed equipment tends to have some exposed main parts within the set and the only reason to insulate them is when that's required to keep the user (not the repairman) safe. Repairmen can only kept safe by using external power supplies that aren't to be repaired (not meant as a real suggestion). Last edited by Maarten; 18th Jan 2019 at 12:45 pm. |
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18th Jan 2019, 4:57 pm | #12 |
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Re: Safety Capacitors X or Y or ?
I agree that there are plenty of places you can get a shock from on a set, if you go under the chassis or near power switch connections etc that are not insulated. However, it is still not good to have those exposed mains connections on top of that transformer on the chassis top area, where it is so easy to accidentally contact them simply reaching into the back of the set to make some adjustment or other, so I still think they are better protected by additional insulation. It would have been better if the mains wiring/transformer connections were under the chassis as they often are.
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18th Jan 2019, 6:36 pm | #13 |
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Re: Safety Capacitors X or Y or ?
Attached is a view inside a Telequipment D67. Quite a few high voltage areas in there, but just look at that mains fuse. I get a piece of white plastic, cut off a "slide binder" for A4 paper. I draw a big red "lightening flash" on the plastic and stick it over the fuse holder. I am sure it could be criticized on the "inadequately safe" basis, but I always find it a timely reminder. The rear of the mains voltage selector is nearby, but much less accessible, and you would almost deserve it if you get your fingers in thee.
Les |
19th Jan 2019, 2:06 am | #14 | |
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Re: Safety Capacitors X or Y or ?
Quote:
I think it does help to cover exposed mains connections like you have done. |
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19th Jan 2019, 4:42 pm | #15 |
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Re: Safety Capacitors X or Y or ?
Many thanks to all on the advice and information and many thanks for the explanations on the X and Y caps and how they are connected.
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