Shell Diala-AX is but one insulating oil... About $25/5 gallon pail last
time I bought it (from L.T. "Lee" Sawyer in Van Nuys, a Shell Jobber)..
Univolt is another brand. Castrol has a brand which I can't remember the
trade name for off hand...
There are various flavors of insulating oil (cable, transformer, and
capacitor) with somewhat different (but irrelevant for antenna/load/etc.
use) properties, unless you're building oil insulated coaxial cable. Castor
Oil is also used as a dielectric (has a higher epsilon than mineral oil...)
Thermal properties are basically the same as USP mineral oil (drugstore
oil). The big differences:
- preservative to keep the oil from going rancid (BHA, BHT, or Vitamin E,
- low water content (USP doesn't care about water content, as long as it's
not precipitating out) - has a HUGE effect on dielectric strength, but
probably no issue for cooling a dummy load.
- very low particulate contamination (dielectric strength)
The important thing for a load is probably the viscosity.... you want a
fairly low viscosity so it can circulate under thermal loads.
Diala-AX smells just like Vaseline (which is no surprise, since, chemically,
it's basically the same thing..just a different carbon chain length).
The cheapest easy source for relatively pure mineral oil is feed stores
(used as an animal laxative).
The cheapest source for not-so-pure mineral oil is the autoparts store...
get straight-weight non-detergent motor oil... It will still have additives,
but it would probably work in a load.
----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: "Mark Beckwith" <firstname.lastname@example.org>; <email@example.com>
Sent: Sunday, June 06, 2004 6:59 PM
Subject: Re: [TowerTalk] Heath Cantenna
> I was in the same situation as you several years ago
> (e.g. I picked up a used cantenna at a hamfest). I dumped
> the old "unknown" liquid into a plastic jug and drew a skull
> and crossbones on the side. I then dried out the remaining
> oil inside the can with paper towels, washed out the can
> with soapy water, dried it, and then refilled it with non-PCB
> transformer oil that I got from MFJ. The MFJ oil is
> expensive, but it's real transformer oil which is supposed to
> have better thermal properties than mineral oil which is
> generally much cheaper (the rated duty cycle of the MFJ
> dummy load is higher if you use transformer oil instead of
> mineral oil) . If you know somebody in the electric utility
> business, you might be able to sweet talk them out of a
> gallon of real transformer oil for free, or as Jim Lux suggests
> check the yellow pages under "oil - jobbers". I am sure the
> wholesale price is a small fraction of the MFJ price. I think
> Shell Diala-X is the brand name:
> BTW, don't spill the transformer like I did. The new stuff may
> not be toxic, but I will ruin leather shoes :)
> 73 de Mike, W4EF............................................
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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