[Amps] Chinese Caps Defective @ RF

[Jim Barber]

Has anyone done RF testing on the big doorknobs used in laser power 
supplies? Many of the 20-40KV caps sold on eBay come from surplus laser 
gear and were not originally sold for RF use.

It would be interesting (to me at least) to run "a few" amps of RF 
current at both 1.8 and 30mhz through one of the big TDK/Murata units 
and see what happens. Relatively speaking, you don't need much current 
handling capacity for plate blocking use, but padding 160m tank circuits 
is another matter.

73,
Jim N7CXI

On 3/24/2012 7:07 AM, Carl wrote:
> While new HEC prices are a bit ridiculous there is enough high quality used
> doorknobs around plus the Russian surplus RF caps are also excellent.
>
> I passed over those Chinese caps as a bad deal years ago once I found the
> actual specs.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Rob Atkinson"<ranchorobbo at gmail.com>
> To:<amps at contesting.com>
> Sent: Saturday, March 24, 2012 9:17 AM
> Subject: Re: [Amps] Chinese Caps Defective @ RF
>
>
>> You have a lot of circulating current through blocking caps on 10 m.
>> For a critical application, I'd stick with a known manufacturer like
>> HEC where you can see a range of specifications and test data.  You do
>> pay more, but you only have to pay one time.   "off-brand" caps can be
>> used in homebrew antenna tuners where it is okay to um, experiment.
>>
>> The dielectric temp. constant is one thing to consider and indeed, the
>> caps should be class 1.   The other factor is the external temperature
>> environment.  For example, are the caps mounted near a tube that
>> throws off a lot of heat.   A good manufacturer will supply an
>> environmental  temperature range spec. that the cap has to stay within
>> to keep its value.
>>
>> 73
>>
>> Rob
>> K5UJ
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