Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 9th 15, 12:10 AM posted to sci.electronics.repair
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Default Capacitor Shield ?

On Sun, 8 Nov 2015, Ron D. wrote:


No real clue except an explosive shield.

There is a polarity on non-polarized caps. It is suggested that the
"foil side" go to the low Z point in the circuit. Typically this would
be important in a vacuum tube circuit. Not all caps are marked alike,
"Foil side" used to be a common marking.

Wait. That sort of "polarity" had nothing to do with DC voltage, but
about which side went to ground. And it was because paper capacitors were
so large, and could be a source of noise pickup if the outer side wasn't
going to ground.

It never really came up because by the time of transistors, the paper
capacitors had mostly faded away.

Michael


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Old November 9th 15, 02:29 AM posted to sci.electronics.repair
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Default Capacitor Shield ?

Mr. Black:

yes.

But, these https://www.tedss.com/2020024048 0.1V 600V modern caps are BIG too.
There is a youtube video of a guy that made a device to help you sort out the foil side. The foil side to the Low Z point makes a lot of sense.
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Old November 9th 15, 02:32 AM posted to sci.electronics.repair
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Default Capacitor Shield ?

On Thu, 5 Nov 2015 17:48:33 -0800 (PST), wrote:

https://dl.dropboxusercontent.com/u/...070%20Caps.jpg
In a Kenwood receiver. It is steel, not aluminum.
What is its purpose ?


Notice the blue and black pair of wires that are carefully routed
around the shield. My guess(tm) is that they carry AC power from the
xformer partly obscured at the top of the photo. Also note that both
ends of the steel shield are at chassis ground through mounting
screws. The steel shield possibly provides some reduction in 60 Hz
(hummmmm) coupling to the power supply filter caps. Later revisions,
that didn't have the shield probably re-routed the AC wiring.


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Old November 9th 15, 02:59 AM posted to sci.electronics.repair
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Default Capacitor Shield ?

I'd agree with that.
Probably there was a hum or buzz in the low level magnetic phono circuits which are very sensitive.
Mark


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Old November 10th 15, 05:55 PM posted to sci.electronics.repair
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Default Capacitor Shield ?

gregz wrote:
Jeff Liebermann wrote:
On Sun, 8 Nov 2015 18:59:21 -0800 (PST), wrote:

I'd agree with that.
Probably there was a hum or buzz in the low level magnetic phono
circuits which are very sensitive.
Mark


Something must be wrong. Nobody ever agrees with me.


I didn't even notice the wire.


I didn't see it either. The shield looks OEM, even with the weird shape.
The plating looks intact and it has no handling marks as if it was rigged
up by somebody- no cut marks, no scratches from pliers etc.

Greg

Marginally related anecdote: The easiest way to tell what something
does is to remove it and see what breaks. I used to own a 1970 Land
Rover Series IIa. In order to replace the spark plugs, I had to first
remove a steel "heat shield". This bothered me as I could see no
reason why a heat shield was necessary in such an open and drafty
engine compartment, with nothing nearby to protect. So, I removed it.
Everything was normal until I hit 57 mph, when the engine compartment
turned into a giant low pitched whistle, which made enough noise to
attract the attention of all the nearby drivers on the freeway.
Apparently the "heat shield" detuned the engine compartment so that it
would not whistle at operating speeds.

Remove the amplifier shield and see what happens. My bet is some low
level hum, that could only be measured on instruments, but which would
affect the advertised noise levels.



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