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Old 9th February 2016, 07:00 PM   #1
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Default How Safe are Ceramic Top Caps?

How safe are the ceramic top caps over 500V?
Could there be possible arcing from the small gap between the bottom of the cap and top of the tube if it is touched?
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Old 9th February 2016, 07:22 PM   #2
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Some of those Chinese top caps would worry me. The small ones, for like a 6KD6 will hardly stay on the tube even.
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Old 10th February 2016, 02:48 AM   #3
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Common alumina ceramic is good for 15KV/mm. Air is more like 3KV/mm, which makes arcing highly unlikely at 500V. The more likely hazard is leakage due to surface crud accumulation, especially in the presence of moisture. I never handle those things until I've verified that no voltage is present!
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Old 10th February 2016, 05:15 AM   #4
ericj is offline ericj  United States
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Quote:
Originally Posted by smoking-amp View Post
Some of those Chinese top caps would worry me. The small ones, for like a 6KD6 will hardly stay on the tube even.
seems like you could just use a small tool like a miniature flathead screwdriver to bend the contacts a bit closer
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Old 10th February 2016, 08:42 PM   #5
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Originally Posted by ericj View Post
seems like you could just use a small tool like a miniature flathead screwdriver to bend the contacts a bit closer
I've tried that, and the results aren't encouraging. Unfortunately, the typical Chinese ceramic anode connectors are very poorly manufactured. The DIY community needs a reasonable alternative.
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Old 11th February 2016, 04:39 AM   #6
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Originally Posted by ericj View Post
seems like you could just use a small tool like a miniature flathead screwdriver to bend the contacts a bit closer
The metal used in these is very soft and deforms readily
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Old 13th February 2016, 08:46 AM   #7
hpeter is offline hpeter  Slovakia
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You are concerned about voltage..
My 2a3 are running at 11w, and touching the glass does burn fingers. That should be enough as do-not-touch-reflex thing
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Old 13th February 2016, 08:00 PM   #8
ericj is offline ericj  United States
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Originally Posted by rotaspec View Post
The metal used in these is very soft and deforms readily
Hm.

Get a high-temperature (red) o-ring that will slip around the metal clips?

I've never used a top cap, just spitballing. I don't know a lot about their construction.
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Old 13th February 2016, 08:33 PM   #9
wa2ise is offline wa2ise  United States
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Back in the days of vacuum tube TV sets, manufacturers used a simple metal spring like thing to grip the top caps of the horizontal output tube. No protection for wayward fingers, but it was figured only TV serviemen, who knew the hazards, would be in there with the power on (TV sets had interlock power cords that would disengage when the back cover was removed). To protect people from ID10T errors.

If your amp is enclosed, then you could use these clips. I never much liked the current fashion of having tubes exposed when the amps are in consumer use.
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Old 17th February 2016, 06:02 PM   #10
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hmm... if you cage your amp it seems you could use something like these.

Click the image to open in full size.
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