[Amps] Chinese Caps Defective @ RF

[Carl]

Ameritron and others seem to get by with Teflon disc caps as Load padders 
and plate blockers in 2000-2500W amps. I havent looked at prices in quite 
awhile.

Carl


----- Original Message ----- 
From: "Jim Barber" <audioguy at q.com>
Cc: <amps at contesting.com>
Sent: Saturday, March 24, 2012 5:39 PM
Subject: Re: [Amps] Chinese Caps Defective @ RF


> 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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