[Amps] load capacitor ratings?

[Will Matney]

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. 
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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