Envelope-to: dave@picks.force9.co.uk Delivery-date: Sat, 04 Feb 2006 17:58:39 +0000 Received: by ptb-mxcore01.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1F5RgD-0000Ac-OT for dave@picks.force9.co.uk; Sat, 04 Feb 2006 17:58:39 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (PlusNet MXCore v2.00) id 1F5RgD-0000AG-Ju for dave@picks.force9.co.uk; Sat, 04 Feb 2006 17:58:37 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1F5Rfb-0001Oy-0W for rs_out_1@blacksheep.org; Sat, 04 Feb 2006 17:57:59 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1F5Rfa-0001Op-Gi for rsgb_lf_group@blacksheep.org; Sat, 04 Feb 2006 17:57:58 +0000 Received: from amsfep14-int.chello.nl ([213.46.243.21]) by relay1.thorcom.net with esmtp (Exim 4.51) id 1F5T0O-0003SO-K8 for rsgb_lf_group@blacksheep.org; Sat, 04 Feb 2006 19:23:47 +0000 Received: from MARLEEN ([24.132.154.183]) by amsfep14-int.chello.nl (InterMail vM.6.01.04.04 201-2131-118-104-20050224) with SMTP id <20060204175331.YMAO18747.amsfep14-int.chello.nl@MARLEEN> for ; Sat, 4 Feb 2006 18:53:31 +0100 Message-ID: <002c01c629b3$e8210240$b79a8418@MARLEEN> From: "PA0WFO" To: rsgb_lf_group@blacksheep.org References: <2dd.1a9abf4.3115576c@aol.com> Date: Sat, 4 Feb 2006 18:53:29 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2670 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2670 Subject: LF: Re: Re: More smoke... Content-Type: text/html; charset=windows-1252 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Content-transfer-encoding: 8bit

Dear All ,

In my Ropex transmitter I have a class D PA with 2 power fets Fairchild RFP 70N06 with rather generous ratings 70 Amps each and a max voltage of 60 Volts the supply voltage is 13.8 Volts and a measured output of 154 Watts . When the antenna is mismatched for whatever reason will the Fets break down on voltage or current peaks ? ( the DC input of 13.8 Volts is properly fused ) and is it possible to prevent voltage breakdown by fitting power zener diodes over the drain and source of both Fets without spoiling their efficiency . A fast overcurrentprotection is included in the circuit . The reason for this question is that we had a breakdown in the Ropex Fet final of PA0VHF while tuning the antenna matching unit out of resonance ( while doing this the input was rather low ) and are wondering what caused it .( The heatsink was not hot at all while tuning up to the rated output )

73,William PA0WFO

----- Original Message -----

From: MarkusVester@aol.com

To: rsgb_lf_group@blacksheep.org

Sent: Saturday, February 04, 2006 2:03 AM

Subject: LF: Re: More smoke...