[Amps] 50 Ohm Loads

[Nils Petter Pedersen]

Hi !
The MP9xxx series resistors from Caddock are excellent, and they have
very low series L .  A 50ohm/100Watt unit is typically 20nH  (nanoHenry).
The problem with the TO-packaged units is that they MUST have a good
heatsink. Without heatsink the burn off for nothing. Cooling surface is too
small to be effective in oil.
They also have the MS series resistors (standard tubular shape) in
low-inductance types. Here 15W (in air) is the highest rating for a value
of 50 Ohms (but you can combine series/parallell)
I am a little careful recommending the MP9xxx series or similar as dummy
load ! Remember that inductance is not the only thing to avoid. Capacitance
is just as important !!  The TO resistors must be flat-packed
against a (metallic) heatsink, sandwiching the ceramic wafer between the
resistance element and that heatsink. That could make an excellent capa-
citor . But I have no idea of the actual values involved. A test is the only 
way.
 My datasheets says nothing about it...
Peter LA7SL
----- Original Message ----- 
From: "jeremy-ca" <km1h at jeremy.mv.com>
To: <d.cutter at ntlworld.com>; "Jim Brown" <jim at audiosystemsgroup.com>; 
<amps at contesting.com>
Sent: Tuesday, November 13, 2007 7:17 PM
Subject: Re: [Amps] 50 Ohm Loads


> Excellent idea David; I never heard of them before. I see that Mouser
> carries the 100W version in stock. Ive just ordered a pair of 100 Ohm from
> Mouser and will see how they look for RF as well as how they hold up at
> power in a Heath Cantenna..
>
> Its a shame that the person who posted that insulting comment to you 
> doesnt
> know how to use Google.
>
> Carl
> KM1H
>
>
>
>
> ----- Original Message ----- 
> From: <d.cutter at ntlworld.com>
> To: "Jim Brown" <jim at audiosystemsgroup.com>; <amps at contesting.com>
> Sent: Tuesday, November 13, 2007 3:31 AM
> Subject: Re: [Amps] 50 Ohm Loads
>
>
>>
>> So far no-one has mentioned non-inductive winding technique.  I think
>> Caddock use a method of winding in one direction, then half way along
>> reverse the direction to complete the winding.
>>
>> David
>> G3UNA
>>
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