Jon Ogden wrote:
>
>Well, I decided to put my money where my mouth is. I took 2 of Rich's 100
>Ohm 3 Watt resistors (6 Watt total dissipation), put them in parallel and
>soldered them to a PL-259. I then hooked them up to the output of my 2
>meter setup which consists of an FT-847 and a Mirage amp which puts out
>about 160 Watts.
>
>The resistors measured 52.1 Ohms before I applied power. After a short CW
>dah at full power output (160 W), I measured the resistors again - 51.2 Ohms
>- within the error of my power meter. Did a little longer dah again. The
>resistors still measured 51.2 Ohms. Lastly, I did a 2 second keydown. The
>resistors started turning a little brown, were quite warm, but were STILL at
>51.2 Ohms.
More data: at DC I've overloaded 2W metal oxide film resistors 10x for a
whole minute. They ran bright red-hot, with lots of smoke from the
paint, but when they cooled down they were still within resistance
tolerance.
Carbon film or solid carbon increase in resistance when grossly
overloaded like that, because the carbon literally burns away.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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