[Amps] load capacitor ratings?

[Will Matney]

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. 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.

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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