Return-Path: Received: from rly-dc04.mx.aol.com (rly-dc04.mail.aol.com [172.19.136.33]) by air-dc03.mail.aol.com (v125.7) with ESMTP id MAILINDC031-b1c4adc82f938; Mon, 19 Oct 2009 11:17:24 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-dc04.mx.aol.com (v125.7) with ESMTP id MAILRELAYINDC048-b1c4adc82f938; Mon, 19 Oct 2009 11:17:16 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Mzty5-0005y8-RJ for rs_out_1@blacksheep.org; Mon, 19 Oct 2009 16:16:17 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Mzty5-0005xz-BM for rsgb_lf_group@blacksheep.org; Mon, 19 Oct 2009 16:16:17 +0100 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Mztxs-0002u5-0l for rsgb_lf_group@blacksheep.org; Mon, 19 Oct 2009 16:16:06 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApsEAMsf3EpZ8rrx/2dsb2JhbACEPNZ5hDEEgVs X-IronPort-AV: E=Sophos;i="4.44,585,1249254000"; d="scan'208";a="40243103" Received: from unknown (HELO mal769a60aa920) ([89.242.186.241]) by out1.ip01ir2.opaltelecom.net with SMTP; 19 Oct 2009 16:15:37 +0100 Message-ID: <003701ca50cf$02ef9af0$0301a8c0@mal769a60aa920> From: "mal hamilton" To: References: <20091019153721.iapc84ciw0owg8cg@mailzone.onetel.net.uk> Date: Mon, 19 Oct 2009 16:15:36 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: AF Amps at 136 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 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-AOL-IP: 193.82.116.20 ----- Original Message ----- From: "Brian G3YKB" To: Sent: Monday, October 19, 2009 3:37 PM Subject: Re: LF: AF Amps at 136 Hi Chris - I built a linear PA for 136 kHz (I wanted it linear so as to run PSK31). It uses four bipolar output transistors (two MJ15003 and two MJ15004) in complement ary parallel/push-pull class AB. I drive them with two other transistors (2SD14 59 and 2SB1037) in darlington configuration - ie a simple "AF amplifier" type of circuit. What is it ? its either an AF AMP or RF AMP. G3KEV The whole lot is fed from a TDA2030. It produces a peak output of 150 watts (from a dual 32 volt supply) and has withstood all sorts of abuse. However it is only 40% efficient (I suspect this may be due to the slew rate of the power transistors). "AF amplifiers" can work! Regards - Brian (G3YKB) Quoting Chris : > Hi All, > Just started constructing TX for 136kHz, noticed Maplin do a Velleman > audio PA kit that is rated at 200W (100W RMS into 4R). OK there's no > mains transformer or heat sink, but reckon it's good value at £14.99. > Point is the specs also say the minus 3db frequency response is 3Hz / > 200kHz. > The RSGB books 'LF Today' refer to using audio amps as PAs at 136 > with 'a few modifications'. Does anybody know where these > modifications are documented? I guess there's nothing major, reduce a > few cap values? Remove Zobel Network etc.?? If anyone has experience > with this approach I would appreciate some hints. Thanks. > Chris, G4AYT, Whitstable. -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.422 / Virus Database: 270.14.20/2444 - Release Date: 10/18/09 09:04:00