Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, RATWARE_GECKO_BUILD autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u09Bvneu000600 for ; Sat, 9 Jan 2016 12:57:49 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aHs6p-0006ro-OV for rs_out_1@blacksheep.org; Sat, 09 Jan 2016 11:55:03 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aHs6p-0006ra-5V for rsgb_lf_group@blacksheep.org; Sat, 09 Jan 2016 11:55:03 +0000 Received: from smtpout.karoo.kcom.com ([212.50.160.34]) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aHs5m-0000pG-Ge for rsgb_lf_group@blacksheep.org; Sat, 09 Jan 2016 11:55:01 +0000 X-IronPort-AV: E=Sophos;i="5.20,544,1444690800"; d="scan'208";a="87567186" Received: from unknown (HELO [127.0.0.1]) ([109.176.223.24]) by smtpout.karoo.kcom.com with ESMTP; 09 Jan 2016 11:53:42 +0000 Message-ID: <5690F4C5.2050008@lineone.net> Date: Sat, 09 Jan 2016 11:53:41 +0000 From: LineOne User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:31.0) Gecko/20100101 Thunderbird/31.1.2 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: In-Reply-To: X-Scan-Signature: 086f3faad0220c9ae57a7913e711a86d Subject: Re: LF: Linear Amp for LF Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 6232 There a few "audio" transistors about, I am using Toshiba complementary pairs 2SA1947 and 2SC5200 (4 of each) with 320W dc input. Naturally there is plenty of heat to dissipate so I fitted large heatsinks and cooling fans, using no insulating pads, the heatsinks are "live". The power supply is linear and.shortly to be upgraded to provide at least 500W dc input. No transmissions at the moment, I have an analogue IQ generator board to fit as my IQ software has failed. Hugh, M0DSZ On 08/01/2016 21:45, Andy Talbot wrote: > Are there any proven reliably designed LF amplifier designs power > amplifiers for 137 / 475? Wideband, covering both ideally Rated > for at least 300 Watts output, and ideally a lot more. > > I saw G3YXM's low-HF design, and it looks promising for low frequency > use, but he appears to have not gone that way and went for a > switchmode version at LF/MF > > Of course, I could just redesign that, or something similar, using > suitable ferrite and a bit of feedback ,but it would be nice to avoid > reinventing too many wheels. > > Using switching MOSFETs as linear amps still doesn't feel quite right, > but enough people seem have managed it now (including my own design > for a low power one) that it looks a sound-enough route to follow up. > The one thing that does bother me about the technique is bias > compensation with temperature. It is really asking for active bias > control, but in a class-B or -AB design, where bias just affects > standing current, that gets more-than a bit tricky as a concept. > > Andy G4JNT