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The printed catalog is apparently outdated.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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