[Amps] 50 Ohm Loads

[jeremy-ca]

That was Carl who wrote that.

As you may know, the Carborundums are fragile being not much more than 
powdered carbon granules molded and held together by some bonding agent.

I used a Dremel cut-off disc and started grinding shallow slots and 
measuring after each one. The result was almost nil so then I turned the 
slots into pie cut wedges. The wedges kept expanding until I had a decent 
valley removed and 50 Ohms. Smoothed out the shape with a round file and 
vacuumed well. Then the wound and a bit of the surrounding area was covered 
with a standard 2 part 3M epoxy resin as used for fiberglassing. Since 
acetone is about the only thing that affects cured resin it was good to go 
into the gallon cans and become pseudo Cantennas for phased verticals and 
general shop use.

Since the value has held I suspect but cant prove that the initial 
manufacturing process caused the resistance to drift soon after production 
and finally stabilized. This may be the reason for a wide range of 
tolerances being offered as well as custom ones at rapidly increasing cost.

For low frequencies a regular wire wound can be used with a capacitor to 
cancel the inductive reactance. Another use for nichrome (;

Carl
KM1H




----- Original Message ----- 
From: "Bruce Lanning" <belanning at verizon.net>
To: <Amps at contesting.com>
Sent: Sunday, November 11, 2007 12:52 PM
Subject: [Amps] 50 Ohm Loads


> Hi, I note with interest what Larry had to say about filling load 
> resisters.
>
> "Bring an Ohmmeter or get a guarantee from a mail order seller as the 
> value
> can change considerably over time. I have a few that were still sealed 
> when
> purchased 100W ones that measured 68-70 Ohms. A little bit of file work 
> and
> sealant returned them to 50 Ohms; they have remained at 50 Ohms for over 
> 10
> years."
>
> Larry I also have filed resisters, but please tell us how you treated a
> carbarundum resister. I for one would be very interested. I have a Bird 
> Load
> that measures 55.6 Ohms and I would like it to be 50 Ohms.
>
> Bruce
> W1GBS
>
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