Message-ID: <001701c3e7dd$dd699a20$1f00a8c0@dellboy>
From: "Dave Pick" <dave@picks.force9.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <6.0.1.1.2.20040129133740.036bcc40@POP3.freeler.nl> <1AmbdK-1Oy81Z0@fwd03.sul.t-online.com>
Date: Sat, 31 Jan 2004 09:37:38 -0000
MIME-Version: 1.0
Subject: LF: Re: Zobel
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: <owner-rsgb_lf_group@blacksheep.org>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Uwe

I had the same problem with QRSS and have decreased the capacitor to 2.2nF.
This still keeps the worst spikes under control when the PA is properly
loaded and has proved reliable.
It all depends on the construction of your output transformer of course.

73
Dave G3YXM.

----- Original Message ----- 
From: "jannsen" <0482183881-0001@t-online.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, January 30, 2004 4:36 PM
Subject: LF: Zobel


> Hi Dave/G3YXM and group,
>
> the Zobel Network 22 Ohm / 4,7nF in my G3YXM PA gets very hot if driving
> the PA in 1kW mode; much hotter than the toroid T2 (output
transformer)gets.
> I changed the five Watt resistor with a  20 Watt, it gets hot too; with
the
> cooling fan off the resistor desolders itself.
>
> I think that`s a good sign of the correct dimension: 22 Ohm / 4,7nF means
> the open reactive load (T2 and surroundings) oscillates at calculated
> 1,539MHz; measured 1,776MHz.
>
> But what a heavy loss!
>
> My question:
> Is there no other possibility eliminating the instability of that output
> system ?
>
> Regards
> Uwe / dj8wx
>
>
>