Envelope-to: dave@picks.force9.co.uk
Delivery-date: Wed, 28 Sep 2005 11:16:43 +0100
Message-ID: <001201c5c40d$fc957780$fd1624d5@jeff>
From: "F6CWN" <f6cwn@tiscali.fr>
To: rsgb_lf_group@blacksheep.org
References: <B333AB0EF6D4D4118BAF00508BAED8EA088DA7A0@mms12014.stv.uk.astrium.corp>
Date: Wed, 28 Sep 2005 10:21:19 +0100
MIME-Version: 1.0
Subject: LF: Re: Advice will be gratefully received
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Hello Chris,

At first,"RIP poor MOS"!

I prefer use MOS with higher VDS.
The driver must absorb energy, because the Ciss capacitance, i use TSC426 or
TC4429 driver.
It sis better to separate the cooling radiators to minimize the reaction
between the two parts
of the bridge (capacity Drain / Ground, the ground is "hot").
A problem with reactive loading, the coils of the LPF are reversible.
A little photography of your PA can help...

73: Jeff / F6CWN/p


----- Original Message ----- 
From: "OSBORN, Chris" <Chris.OSBORN@astrium.eads.net>
To: "LF Group (E-mail)" <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, September 28, 2005 10:43 AM
Subject: LF: Advice will be gratefully received


>
>
>
> The PA FET's in my new home brew transmitter keep exploding !
>
> I'm using push-pull  IRF520's rated at 100 V Vds and my supply is 30
> volts.
> I am careful not to exceed the V gs.
>
> The gates are driven with a toroidal transformer and the whole
> circuit is just a scaled up version of my original TX, which works fine.
> It generates healthy power into a 50 ohm dummy load but on
> connection to the aerial circuit - bang !
> The aerial system is identical to that used with the old TX !
>
> Has anyone any ideas on what's causing the problem and how to cure
> it ?
>
> I'm running out of FET's and my nerves are somewhat frayed (shell
> shock!)
>
> 73 Chris G3XIZ