[Amps] load capacitor ratings?

[R.Measures]

On Aug 30, 2004, at 11:54 PM, Will Matney wrote:

> I wanted to take a look at OEP's variable inductor and see what it 
> said on their website and in the catalog I have here. The website says 
> they're using a glass-phenolic core. The printed catalog said it had a 
> teflon-delrin polymer core.
>
> From website;
>
> The new R128C is completely non-magnetic, and all materials are chosen 
> for high electrical and thermal conductivity and low loss in RF 
> fields.

Will -  If the coil form no longer contains Delrin, it should be okay.  
The printed catalog is apparently outdated.

> The plated #10 copper bus wire rests in a precision-machined helical 
> groove cut into a glass-based phenolic tubular core. This core turns 
> on two large sealed stainless steel ABEC-5 instrument bearings seated 
> in machined Ultem frames. Incorporated into the design are two of the 
> RF-proven high-amperage rotary contacts originally designed for 
> high-end variable capacitors.
>
> Will Matney
>
> R. Measures wrote:
>
>>
>> On Aug 30, 2004, at 10:52 PM, Will Matney wrote:
>>
>>> Rich,
>>> This insulation material that they said was nylon, looked as if they 
>>> dipped the stator assembly in it as a liquid and let it dry. It 
>>> still gave enough clearance for the rotor plates to move freely. 
>>> They guaranteed it to be rated for X2 the rated air voltage.
>>
>>
>> Sure, for DC.
>>
>> >
>>
>>> I never tried one so can't say how they worked. I couldn't see 
>>> paying that kind of price for a small unti when going up one or two 
>>> sizes in an air variable was all that was needed and was almost the 
>>> same price as the smaller one.
>>>
>>> I wasn't aware of the problems they had with the roller inductors as 
>>> I never did try one of theirs to use it. I knew they made them but 
>>> had never heard about any problems. Of course this is something a 
>>> manufacturer is going to announce either.
>>
>>
>> Nor a magazine that carries their advertising.   QST carries MFJ ads. 
>>  The tuner ignition was not reported in QST.
>>
>>>
>>> Will Matney
>>>
>>> R. Measures wrote:
>>>
>>>>
>>>> On Aug 30, 2004, at 5:37 PM, Will Matney wrote:
>>>>
>>>>> Rich,
>>>>> Exactly. I talked to the owner of Oren Elliot (Orens son Stephen) 
>>>>> several years ago about this and what he thought the rating should 
>>>>> be. He had several thoughts on this but told me that most were 
>>>>> using a X2 rating the same as the coupling capacitor for tune C.
>>>>
>>>>
>>>>
>>>> -   A x2 Vdc Tune-C (6kV) is what the TL-922 uses and the result is 
>>>> frequent loss of the bandswitch - which has a 5kV withstanding 
>>>> ability.  It is better to have a Tune-C flashover than a bandswitch 
>>>> flashover.
>>>>
>>>>> He recommended using a load C with a voltage rating some higher 
>>>>> than the peak voltage rating across the load, generally having a 
>>>>> 50 ohm load as standard. I think he figured by a sometimes varying 
>>>>> load, it could take more voltage to create the same power across a 
>>>>> mis-matched load. Of course this could sure be the case and is 
>>>>> something I would not have thought of at the time. Not all 
>>>>> antennas are a perfect 50 ohms or close to it. His capacitors are 
>>>>> tested in open air with a hipot tester. They had a jig made up 
>>>>> with a nut driver handle made onto a coupling to turn the rotor 
>>>>> with. They applied the hipot and turned the rotor through its 
>>>>> rotation to catch any arcing. My concern was the physical size of 
>>>>> air variable capacitors and what was the least size I could safely 
>>>>> get by with. He did mention that one was available where the 
>>>>> plates had a "nylon dielectric" to insulate the stator plates 
>>>>> raising a .016" air gap to 1100 V (X2).
>>>>
>>>>
>>>>
>>>> Will --
>>>> -  Nylon is a good DC insulator, but it has the worst D 
>>>> (dissipation)-factor I know of.  Another lossy RF dielectric is 
>>>> Delrin -- which is what Elliot used in their roller-coils a few 
>>>> years back.  MFJ used one in their "3kW" tuner.  When this tuner 
>>>> was tested in the ARRL Lab, it caught fire with 900w of AØ/NØN.  An 
>>>> easy fix is to make the roller-coil form out of G-10, G-11, or ABS.
>>>>
>>>> cheers
>>>> ...
>>>>
>>>>
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>>>
>>>
>>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>
>>
>>
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>>
>
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org