The outer shell over the Cantenna resistor is used to maintain the
impedance so you will need to make another shell with the proper
diameter. THere are formulas available to calculate the required diameter.
The Cantenna resistor is 200 W in open air. When you stick it in a can
and in a shell , it is not able to rid itself of the heat. Add oil and
things get better where the oil will transport the heat to the sides of
the can and also the oil can accept some heat for a limited time. THe
oil but mostly the air in the can expand so a vent is a good idea.
You have the makings for a nice load.
---
Ron
BEAR wrote:
>
> Anyone out there have solid technical information on Dummy Loads &
> Carborundum Resistors??
>
> My old Heathkit Cantenna has a ~1" dia x ~5" (iirc) grey carborundum
> resistor,
> sitting in a can of oil. (rated 1kw short time)
>
> I've been offered a batch of ~1" x 18" carborundum resistors @ 50 ohms
> and/or
> a batch of ~2" x 18" @ 25 ohms - these are said to be rated at 750
> watts.
>
> Here are my Q's:
>
> If the latter one is rated at 750 watts, what is the dry rating of the
> Heath
> likely to be??
> (the heath is asymptotic to 200 watts over time...)
>
> What is the bandwidth likely to be ??
> (the heath is <1.5:1 up to 300 mhz.)
>
> If I put it in a bath of transformer oil, what is the increase in
> power handling?
> (does the added surface area play in to this??)
>
> I'm thinking that unless there is something wierd about these
> resistors that
> the 50 ohm unit ought to be at least 500 watts in air, or more... the
> 25 ohm
> unit would seem to be rated very conservatively, yes?
>
> I've owned a bird style >2kw unit at different times and they seem to
> be about
> this depth and have fins for cooling (of course) - do they just leave
> some air in
> the chamber for heat expansion of the oil, do they have a blow off vent??
>
> What else should I know???
>
>
>
> _-_-bear
>
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