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death cap question

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Posted on March 14, 2017 at 17:20:33
gkargreen
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Need to replace a death cap in the Scott preamp, its a .022 uf cap. Seems I remember someone saying to use a certain type of cap in these situations, can anyone remind me what that was? Thanks

 

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RE: death cap question, posted on March 14, 2017 at 17:27:39
Uncle Mike
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A brief tutorial

 

RE: death cap question, posted on March 14, 2017 at 17:31:29
gkargreen
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Thanks, Mike, I seem to remember something like an XY... cap as the recommended type, do I need to replace with the same exact value, ie., .022 uf?

 

RE: death cap question, posted on March 14, 2017 at 17:40:03
Uncle Mike
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Yes, do NOT go larger (look up capacitive reactance to understand why). Get a 600V rated cap too.

 

RE: death cap question, posted on March 14, 2017 at 18:23:33
Steve O
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A "death cap" should be replaced by a type "Y" or dual rated "X/Y". Not sure what you mean by 600V but these caps generally carry an AC rating when listed by safety agencies. 250VAC is sufficient for US mains. 600VDC may or may not be. Also, there's a limit on AC current thst can be passed and still be considered safe. I recall (so don't quote me on this) something like 0.3 or 0.4mA which @ 120VAC equates ~ 0.008uF max. Point here is that it's worth a little research to replace with safe value and that 0.02uF is probably too large by today's standards.

 

RE: death cap question, posted on March 15, 2017 at 18:32:21
Thermionic27609
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Would it be appropriate to ask why you need to replace one of these? Many pieces of vintage gear never used them. Their original purpose was to shunt any RF picked up by the chassis to AC neutral.

In other words, are you replacing it because it's there or because there's an RF problem in this preamp's location?

 

RE: death cap question, posted on March 15, 2017 at 18:39:47
Thermionic27609
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I looked over a few Scott preamps, and I believe only one used a capacitor on the AC. That one had a capacitor across the AC line for noise filtering. Across the AC line is technically not a death cap because it's not directly connected to the chassis.

 

RE: death cap question, posted on March 15, 2017 at 18:49:47
gkargreen
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This one is an old pyramid cap connected across the AC line after the fuse, these old Pyramids are pretty sketchy...

 

RE: death cap question, posted on March 15, 2017 at 18:51:22
gkargreen
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That's right! So, I would just use another .02 ufd cap of the appropriate voltage, correct?

 

RE: death cap question, posted on March 15, 2017 at 23:25:08
Thermionic27609
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The LC-21 is the only Scott schematic I can see that uses a line filter capacitor, and that one is always under voltage whenever the preamp is plugged in. But it might be a running change in production in one of the others.

You might still get an X or X2 rated capacitor since these are designed as line filters, but any quality polypropylene capacitor would probably do.

 

RE: death cap question, posted on March 19, 2017 at 08:54:39
Crazy Dave
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I thought you were supposed to use a ceramic disk capacitor for this.

Dave

 

RE: death cap question, posted on March 29, 2017 at 13:29:10
Thermionic27609
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X2 rated film capacitors are designed for across the AC line use.

 

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