On Aug 15, 2004, at 4:30 AM, Larry Carman wrote:
I have ten 890 AS carborrundum resistors. They are supposed to be 330
ohms 5% but they measure 400 to 500 ohms. Is it the norm that these
resistors change that much with age?
Larry -- Usually they increase in value when they have been
overloaded. Have you got one that's close to 450-ohms that you are
willing to sell or trade? I need a 450-ohm unit for the Class A 1400w
amplifier project. I have a 360-ohm for trade.
Are they still ok to use for a
dummy load at there rated power ( 100 watts each, I think )??? All ten
of these guys parralleled come to 56 ohms. When I put the 259B to them
to check swrs, I end up with 1.3 swr at 2 MHz and 10 plus at 30 MHz.
With a variable 1000 pf capacitor in series, I can tune the swr
to nil to about 24 MHz. Probably would tune above 24 MHz ok if the cap
had a lower minimum pf. I'd like to make an air cooled 3 KW dummy load
from these if I could.
A tapered ground plane is the usual way of reducing SWR.
Regards,
Larry N5BIp
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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