[AMPS] Carborrundum Resistors

[R.Measures]

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