Return-Path: Received: (qmail 58736 invoked from network); 22 Jan 2004 16:13:27 -0000 Received: from unknown (HELO ptb-mxscan01.plus.net) (212.159.14.235) by ptb-mailstore01.plus.net with SMTP; 22 Jan 2004 16:13:27 -0000 Received: (qmail 7782 invoked from network); 22 Jan 2004 16:13:27 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore01.plus.net (212.159.14.215) by ptb-mxscan01.plus.net with SMTP; 22 Jan 2004 16:13:26 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim) id 1AjhSP-0001uc-VD for dave@picks.force9.co.uk; Thu, 22 Jan 2004 16:13:26 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AjhRH-0003X5-3i for rs_out@blacksheep.org; Thu, 22 Jan 2004 16:12:15 +0000 Received: from [194.247.47.231] (helo=mailout.zetnet.co.uk) by post.thorcom.com with esmtp (Exim 4.14) id 1AjhRG-0003Ww-I2 for rsgb_lf_group@blacksheep.org; Thu, 22 Jan 2004 16:12:14 +0000 Received: from irwell.zetnet.co.uk ([194.247.47.48] helo=zetnet.co.uk) by mailout.zetnet.co.uk with esmtp (Exim 3.36 #1 (Debian)) id 1AjhRG-00036H-00 for ; Thu, 22 Jan 2004 16:12:14 +0000 X-Fake-Domain: johnb5a82ea1a4 Received: from johnb5a82ea1a4 (bts-0870.dialup.zetnet.co.uk [194.247.51.102]) by zetnet.co.uk (8.12.3/8.12.3/Debian-6.6.zet1) with ESMTP id i0MGC8Vw002847 for ; Thu, 22 Jan 2004 16:12:13 GMT X-Bad-Message-ID: no DNS (johnb5a82ea1a4) Message-ID: <006801c3e102$8c730c00$6633f7c2@johnb5a82ea1a4> From: "John Rabson" To: rsgb_lf_group@blacksheep.org References: <000c01c3e02e$600a21a0$01eafc3e@l8p8y6> Date: Thu, 22 Jan 2004 16:11:25 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: LF: Re: SOFT START Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.60 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 2 It's when a bank of capacitors totalling a quarter of a Farad at 24 volts is connected with wrong polarity that things start to get spectacular. 73 John G3PAI ----- Original Message ----- From: "hamilton mal" To: Sent: Wednesday, January 21, 2004 2:53 PM Subject: LF: SOFT START Hi All Surprisingly, most high power amps do not have a SOFT START, and judging by the thump at times on switch on, it is even more surprising that the power supply does not explode. In recent times I use a variac and gradually adjust it to full voltages. This is overkill and a more simple cct would suffice. I lost one mains transformer a few years ago and the replacement cost more than the amp was worth. Some of the PSU'S for low voltage high current FET AMPS used in LF applications are even more vunerable ie 12 - 24 V at 20 - 100 A. Most Amateurs that I have spoken to do not realize the danger involved. One of the bean can size electrolytics 200 mfd capacity exploding would be like firing a mortar, probably demolish the house in some cases. The stone built country house would probably survive.If you are dabbling with QRP there is no need to worry. 73 de Mal/G3KEV