[TowerTalk] HN-31 Heathkit Dummy Load

Michael Tope W4EF at dellroy.com
Wed Apr 5 03:16:54 EDT 2006

----- Original Message ----- 
From: <jcowens at NETSCAPE.COM>

> Is anyone familiar enough with the HN-31 Heathkit Dummy Load (History 
> Lesson)to know how much power you can run to this thing in other than "key 
> down". I don't know if it has transformer oil or Mineral Oil in it. Will 
> it handle 1500W on a 50% duty cycle for a short time?? Does anyone know 
> where I can buy transformer oil, or has OSHA outlawed it by now??
> John Owens - N7SEJ


Here is a link to the manual for the MFJ-250 "cantenna" style
dummy load:


The derating curve in this manual is identical to the derating curve
on the side HN-31 cantenna (it looks like the same picture). Its
relatively expensive (~5 to 6 times the price W6RMK noted
for an oil jobber), but if your looking for convenience, you can
buy a gallon of transformer oil from MFJ and have it shipped to
your front-door with a minimum of fuss. Using the MFJ supplied
oil, I've run my HN-31 at 1500 to 2000 watts when testing
amplifiers. The oil gets damn hot so you have to keep the duty
cycle low, but otherwise it seems to work fine. If you have a
peak reading wattmeter, you can use a tuning pulser or a simply
a CW keyer to tune at reduced duty cycle. This will save wear
and tear on your finals and keep the heat down in the HN-31.

Mike W4EF...........................

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