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 Spark Plates
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 Return to top of page · Post #: 1 · Written at 10:53:45 AM on 15 September 2011.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 466

One of my old car radios has 3 Spark Plates.

One on the 12volt input line, and one on each of the speaker leads.

Why use a Spark Plate and not an electrolytic capacitor??

What capacity are Spark Plates??


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Cheers, Ian

 
 Return to top of page · Post #: 2 · Written at 3:25:57 PM on 15 September 2011.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
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 Postcount: 7395

They were probably fitted in the days before condensers were fitted to distributors and without the condenser on the distributor a lot of suppression would be required to keep high tension interference from the ignition system out of the radio.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 4:02:35 PM on 15 September 2011.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 466

Thanks Brad, Any idea of value??


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Cheers, Ian

 
 Return to top of page · Post #: 4 · Written at 5:16:56 PM on 15 September 2011.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7395

To be honest I am not sure. I've never seen one in the flesh so I can't even have an accurate guess. Being a dry condenser I would suggest they are designed to last pretty much forever though.

On an unrelated note, it looks like I will be busy tonight - I can see that several spam robots have been signing themselves up to the site over the last few days. I'll have to close the accounts they've opened and try and find a way to block them.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 5 · Written at 1:47:29 AM on 3 March 2012.
radiola49's Gravatar
 Location: Maryborough, VIC
 Member since 8 December 2007
 Member #: 204
 Postcount: 36

HiTinkera123
Distributors have ALWAYS had condensers, even Magnetos have them! Without the condensers, they would not function.
Maybe Brad was thinking of the suppression condensers that were added to ignition feed, generator, even wiper motors etc to prevent unwanted noise getting into the AERIAL of the radio.
I did come acrross the reason for a spark plate rather than just a large paper cap recently, but can't recall it just now.
Surprising that they are fitted to both speaker leads though.
Lets just say it is completing the integtrity of the shielding of the tin box enclosure of the automotive radio.


 
 Return to top of page · Post #: 6 · Written at 9:59:04 AM on 3 March 2012.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 466

Thanks radiola49,

Yes, I agree with your condenser comments.
Both the radio and car are now in good shape.

Ian


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Cheers, Ian

 
 Return to top of page · Post #: 7 · Written at 2:01:05 PM on 3 March 2012.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5389

What seems to have been overlooked is the "Kettering ignition".

The capacitors on the points of distributors and magneto's are not there principally for suppresion. In most cases it is for quenching and stopping the points being erroded.

The ignition coil of a "Kettering system": develops considerable back EMF and that "spike" can be several hundred volts and needs to be quenched as it will ride on the 12V circuit. If the set is solid state. that can be nast y.

Theoretically two opposing but not touching conductors (plates) can be set at a critical voltage e.g. (lightening arrestor) so that any over voltage will flash over and does (in the case of lightening) not have to be a capacitor.

Any one having doubt can get a real "kick" out of proving me right, by placing a finger on the battery side of a Kettering coil.

Marc


 
 Return to top of page · Post #: 8 · Written at 10:29:22 PM on 3 March 2012.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7395

Maybe Brad was thinking of the suppression condensers that were added to ignition feed, generator, even wiper motors etc to prevent unwanted noise getting into the AERIAL of the radio.

Yep. In the years leading up to distributorless ignitions, cars were more often fitted with two condensers - one for the breaker points, driving the spark when the points break via a back-EMF as Marc described, and another outside the distributor or closer to the radio to suppress the noise from the ignition system. The first condenser is wired in parallel with the points and on the load side of the ignition coil and the second, if fitted is in parallel with the line side of the coil.

In 1988 when Holden released the VN model Commodore, the distributorless ignition found its way into a mass-produced Australian car for the first time and these pretty much did away with the need for replacing condensers and effectively abolished the need for tune-ups - there was nothing left to tune up as computers took over the role of ignition timing.


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A valve a day keeps the transistor away...

 
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