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 Post subject: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 1:38 am 
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C87 on my Zenith H2445R (chassis 24H21) is listed as a line filter with a value of 0.0047uF (600V).

Image

Image

According to the Just Radios website it looks like I need a Y2 safety capacitor to replace this. Problem is that Just Radios safety capacitors are only rated to 250V. Did Zenith rate these for a higher voltage because safety capacitors did not exist back in 1951? Will a safety cap rated at 250V suffice or do I need to try and find one rated for 600V?

The full schematic can be found here:

https://drive.google.com/file/d/0BzQx4cDSWtozaGF3d1E5NzRkd3M/view?usp=sharing


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 2:05 am 
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That rating for the safety cap is AC. 250VAC is the RMS value---peak is root 2 higher------250 * 1.414 = 353
But---AC and DC ratings are based on different factors, so you can't really do a direct conversion

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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 2:19 am 
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Is the 600V requirement per Zenith AC or DC?


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 2:23 am 
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When you see a cap voltage spec--and it does not say DC or AC, it is almost always DC. In older radios, you will typically not see any caps with an AC rating.

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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 2:44 am 
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OK, thanks.

After reading about safety caps on the Just Radios site (and all of their safety caps are rated for 250-275 VAC) I just assumed that since a safety cap was recommended for line filters that it automatically implied that it was an AC application.

http://www.justradios.com/Y2capacitors.html

From their site:

"Y2 Safety/Interference Suppression Film Capacitors are specifically made for high voltage AC (alternating current) applications. Y2 safety capacitors can safely be used as line-to ground / line isolation, across the line / line filter capacitors and antenna coupling capacitors in vintage tube electronics. These safety certified capacitors can also improve the performance of your radios/hi-fi's/Amps/TV's due to their NOISE INTERFERENVE SUPPRESSION characteristics. Back when your vintage tube electronics were manufactured there was a lot less noise interference and Y2 safety capacitors had not been invented. You can improve the safety, reliability and performance your tube electronics by replacing your old/original paper line-to-ground / line isolation / line filter capacitors with new safety approved capacitors.'


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 4:18 am 
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The voltage rating of a safety cap is for the voltage of the AC line it will be connected to and includes an allowance for the voltage spikes expected on an AC power line of that voltage.. When your Zeneth was made there were no safety caps made. All caps of that vintage had a DC voltage rating. The safety cap can take voltage spikes greater than 600 volts.

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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 8:51 am 
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So if I purchase this safety cap from Just Radios will it suffice in my application for C87:

http://www.justradios.com/Y2capacitors.html

Or should I just get a standard cap of 0.0047 rated for 600V DC?


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 12:07 pm 
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Use safety caps for anything connected to the AC line.
Across the line: X1
Line to ground: Y2

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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 4:26 pm 
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I understand that. In a radio schematic it is pretty clear where the AC line is. In this TV not so much to me. Is a line filter always on the AC line in a TV? I assume the interlock in the schematic above is the incoming AC. So my question is will the one from Just Radios rated at 250 VAC work in my application or do I need to get one rated for 600V DC?


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 4:52 pm 
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250VAC safety cap is what you should use.


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 5:04 pm 
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bandersen wrote:
250VAC safety cap is what you should use.

Thanks!


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 5:11 pm 
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Geoff wrote:
I understand that. In a radio schematic it is pretty clear where the AC line is. In this TV not so much to me. Is a line filter always on the AC line in a TV? I assume the interlock in the schematic above is the incoming AC. So my question is will the one from Just Radios rated at 250 VAC work in my application or do I need to get one rated for 600V DC?


C87 is shown between one side of the AC power line and ground. The AC line comes in through the interlock connector shown above R117. AC line filters are either across the line or from one side to ground.


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Wed 04, 2017 6:13 pm 
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Kevin Kuehn wrote:
Geoff wrote:
I understand that. In a radio schematic it is pretty clear where the AC line is. In this TV not so much to me. Is a line filter always on the AC line in a TV? I assume the interlock in the schematic above is the incoming AC. So my question is will the one from Just Radios rated at 250 VAC work in my application or do I need to get one rated for 600V DC?


C87 is shown between one side of the AC power line and ground. The AC line comes in through the interlock connector shown above R117. AC line filters are either across the line or from one side to ground.

Thanks Kevin.


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Thu 05, 2017 8:45 pm 
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Since a schematic is already posted I'll ask this here: what is the purpose of R117, the resistor to ground from the AC line?


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 Post subject: Re: Line Filter/Safety Cap Question
PostPosted: Jan Fri 06, 2017 12:50 am 
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kuchak wrote:
Since a schematic is already posted I'll ask this here: what is the purpose of R117, the resistor to ground from the AC line?


Best I can tell it allows any static(DC voltage) built up on the chassis ground to drain back to the return side of the AC line. In theory that side of the AC line returns to earth ground. For safety reasons the 100k resistor doesn't allow a lethal amount of current to flow in case the AC line plug accidentally gets revered in the outlet, which is why I believe it's typically called a ground isolation resistor. This was back before our modern 3rd prong isolated ground return that now days would connect directly to the metal chassis.


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