[Heathkit] WTB: Heathkit HN-31 cantenna.

[Jim Shorney]

On Sun, 3 Jan 2010 11:50:22 -0800, Edward B Richards wrote:

>Also need to know where to
>get the oil

>From the 1985 Radio Amateur's Hanbook, pp.34-17 to 34-19:

Selection of the coolant for the resistor involved a lengthly
investigation. The use of PCB transformer oils is illegal and involves
a serious health hazard. The investigation did identify several
modern-day transformer and heat transfer oils that could be used, but
none are available for purchase in any quantity less than a 55-gallon
drum. Transformer oil has lower viscosity. That means lower resistor
tepmeratures, but at the penalty of using an oil with a 140 to 150 C
flash point (vaporization temperature). Transformer oil is also treated
to remove water, but maintaining this dry condition is difficult and
expensive. Calculations of the fluid heat transfer show that turbulent
nature convection flow exists for rated power levels. The use of higher
viscosity oil produces higher resistor temperatures, but the gain in
flash point temperature is greater than the rise in resistor
temperature. Oils designed for heat transfer have flash points in the
230 to 250 C region.

  Heat transfer oils are composed predominantly of mineral oil. Highly
refined or medicinal mineral oil has a usably high flash point but at
an undesirably high cost. Heat transfer oils contain small amounts of
rust and oxidation inhibitors, making them preferable to mineral oils.
Heat transfer oils are not available in small quantities, but in at
least one case the very same product is relabeled and sold in 5 gallon
cans for service as a "turbine oil". That product is sold by TEXACO
distributors as Regal Oil R&O No. 46.

  Use of automotive and transmission oils is undesirable. They are
composed of a wide mixture of oils with different flash points. Motor
oil additives will damage the metal platings on an RF resistor. There
is no danger in the short term use of automotive oils, but the
long-term effects are a problem. Further, there are no economic
advantages with automotive oils, as they cost as much as turbine oil.

--from the "Super Dummy" construction article, designed by ARRL TA Dick
Jansson, WD4FAB.



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