[Amps] More parasitic choke questions

[Martin Sole]

This was somewhat germane to my original question. Really more about how
much preferred a purely carbon resistor would be to one of the more modern
equivalents. Having done a little digging, RADCOM July 2005 and August 2009,
In Practice column, Ian writes that paralleled MF resistors are the
components of choice for parasitic suppressors of HF power amplifiers. The
paralleled bit being more to minimise the associated inductance than
specifically increase power handling. This suggests to me that using MF is
not likely to be akin to using WW, rather any impact on suppressor
performance should be minimal and unnoticed in normal use with  what has
otherwise been a very stable amplifier.

I'm thinking 4 resistors in a boxlike arrangement for use in the Henry where
these will fit inside the original coils. For the Alpha 78 I may reduce the
coil length to account for any increase in coil diameter when wound to fit
over two or three MF resistors.

Steve, I couldn't find your 30 Aug 06 post, found several others around that
time on similar topics but would still be interested to know what you
measured.

Cheers
Martin, HS0ZED


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Steve Thompson
Sent: 27 July 2010 13:36
To: amps at contesting.com
Subject: Re: [Amps] More parasitic choke questions

> It does seem though as
> if the preferred carbon composition resistors are no longer easily found.

What is preferred about carbon comp? Given the heat and the need for long
term stability in value they're the least suitable component you could
choose.

Some years ago I measured some different suppressors(results in a posting on
30 Aug 06), subsequently I swapped the carbon comp resistors for MOX on a
couple of them, and couldn't measure the difference. Whenever I measure 2 or
3W MOX resistors in the 20-100 ohms range, the inductance is in the regions
of 2-3nH, which has minimal impact in a suppressor. Inductance is higher in
the 5W ones I've tried.

Steve
_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps