Envelope-to: dave@picks.force9.co.uk Delivery-date: Thu, 29 Sep 2005 19:13:11 +0100 Received: by ptb-mxcore13.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1EL2u6-0005xm-HE for dave@picks.force9.co.uk; Thu, 29 Sep 2005 19:13:11 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore13.plus.net with esmtp (PlusNet MXCore v2.00) id 1EL2u6-0005xT-6b for dave@picks.force9.co.uk; Thu, 29 Sep 2005 19:13:10 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1EL2t8-0001Gb-4Q for rs_out_1@blacksheep.org; Thu, 29 Sep 2005 19:12:10 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1EL2t7-0001GS-It for rsgb_lf_group@blacksheep.org; Thu, 29 Sep 2005 19:12:09 +0100 Received: from sp0169.sc1.cp.net ([64.97.136.169] helo=n066.sc1.cp.net) by relay2.thorcom.net with esmtp (Exim 4.51) id 1EL3fy-0003DR-Iz for rsgb_lf_group@blacksheep.org; Thu, 29 Sep 2005 20:02:39 +0100 Received: from l8p8y6 (62.252.233.11) by n066.sc1.cp.net (7.0.038) id 432A19D2003AB487 for rsgb_lf_group@blacksheep.org; Thu, 29 Sep 2005 18:11:58 +0000 Message-ID: <000e01c5c516$dff5afa0$0be9fc3e@l8p8y6> From: "hamilton mal" To: rsgb_lf_group@blacksheep.org Date: Thu, 29 Sep 2005 17:56:57 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4807.1700 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4807.1700 Subject: LF: LF AMPS 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
For trouble free and rugged amplifiers on LF a tube is the only reliable approach. The type of antennas used by the majority of LF radio amateurs are totally unreliable, poor insulators, antenna moving around in the wind, variations in wx dry or wet and other considerations. These conditions cause considerable variations in antenna impedance, resulting in sudden mis matches, high swr etc and except you have a high degree of protection the FETS will not survive. Tubes also suffer but seldom are destroyed.
Those using the rugged Decca Jeep fet amps (5501 amps) also suffer the same fate. The majority of users have blown the fets.
Using fet amps into a dummy load is a totally different story, no variations in load and total reliability, but connecting to the average amateur LF antenna will produce loud bangs and smoke.
Using QRS especially above 3 sec dots duration is just waiting for a disaster to happen!! 60 or 120 sec dot duration is a killer for prolonged QSO'S
Go for a tube but watch those very high anode voltages like 3k. YOU could expire prematurely.
73 de Mal/G3KEV