Return-Path: Received: (qmail 34665 invoked from network); 21 Jan 2004 18:42:46 -0000 Received: from unknown (HELO ptb-mxscan02.plus.net) (212.159.14.236) by ptb-mailstore01.plus.net with SMTP; 21 Jan 2004 18:42:46 -0000 Received: (qmail 25779 invoked from network); 21 Jan 2004 18:42:46 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore02.plus.net (212.159.14.216) by ptb-mxscan02.plus.net with SMTP; 21 Jan 2004 18:42:44 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1AjNJM-0006V1-Fw for dave@picks.force9.co.uk; Wed, 21 Jan 2004 18:42:44 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AjNIa-0004fq-BE for rs_out@blacksheep.org; Wed, 21 Jan 2004 18:41:56 +0000 Received: from [62.253.164.43] (helo=mta3-svc.business.ntl.com) by post.thorcom.com with esmtp (Exim 4.14) id 1AjNIX-0004fV-Ol for rsgb_lf_group@blacksheep.org; Wed, 21 Jan 2004 18:41:53 +0000 X-Fake-Domain: l8p8y6 Received: from l8p8y6 ([62.252.234.1]) by mta3-svc.business.ntl.com (InterMail vM.4.01.03.37 201-229-121-137-20020806) with SMTP id <20040121184149.QNFJ8999.mta3-svc.business.ntl.com@l8p8y6> for ; Wed, 21 Jan 2004 18:41:49 +0000 X-Bad-Message-ID: no DNS (l8p8y6) Message-ID: <000c01c3e02e$600a21a0$01eafc3e@l8p8y6> From: "hamilton mal" To: rsgb_lf_group@blacksheep.org Date: Wed, 21 Jan 2004 14:53:17 -0000 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 V6.00.2800.1106 Subject: LF: SOFT START Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.7 required=5.0 tests=DATE_IN_PAST_03_06,HTML_20_30,HTML_MESSAGE,SUBJ_ALL_CAPS 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 Content-transfer-encoding: 8bit

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