[AMRadio] Building the Dummy Load

[Donald Chester]

>From: RoadKing <hogtamer at wt.net>
>
>Do you know of or do you have a schematic of such a high wattage Dummy
>Load?  ...I would like the source of the "Glowbars" and a
>schematic if you have one or if its in one of the older Handbooks,


Mine consists of 12 600-ohm glowbars wired in parallel.  I'm not sure of the 
power rating, but they are each about 18" long, so I would say 150-200 watts 
each, so I would say it would be good for a couple of kilowatts continuous, 
and probably 5 or 10 kw for brief periods.  The resistors are hollow inside, 
so they should be mounted vertically, so that the inside of the hot resistor 
acts as a chimney to cause convection currents of air to flow without any 
fans.  I mounted mine in a circular pattern, so that the whole thing is a 
cylinder, about 8" in diameter and about 20"  high with all the hardware 
attached.  It measures within a fraction of an ohm of 50 ohms.

I am not sure of glowbars are still available new.  I got mine from an 
estate.  They were n.o.s. sitll packed individually in the manufacturer's 
boxes.  I suspect the original owner had planned to build just what I built 
with them, since there were exact 12 in the lot.

The Cantenna uses a smaller glowbar, rated at 100-150 watts, and by 
submerging it in oil, it will dissipate close  to a kilowatt for a few 
minutes.  I recall the instructions saying the duty cycle is limited to 5 
minutes continuous.

Don K4KYV

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