Return-Path: Received: from rly-db02.mx.aol.com (rly-db02.mail.aol.com [172.19.130.77]) by air-db08.mail.aol.com (v125.7) with ESMTP id MAILINDB082-ab04adb1d27d7; Sun, 18 Oct 2009 09:50:46 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-db02.mx.aol.com (v125.7) with ESMTP id MAILRELAYINDB026-ab04adb1d27d7; Sun, 18 Oct 2009 09:50:33 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1MzW8z-0002hz-4k for rs_out_1@blacksheep.org; Sun, 18 Oct 2009 14:49:57 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1MzW8y-0002hp-Mh for rsgb_lf_group@blacksheep.org; Sun, 18 Oct 2009 14:49:56 +0100 Received: from out1.ip06ir2.opaltelecom.net ([62.24.128.242]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1MzW7P-0003Rz-MT for rsgb_lf_group@blacksheep.org; Sun, 18 Oct 2009 14:48:20 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AsQEACK62kpcGJKG/2dsb2JhbACCJy6BaIkSBslZhDEE X-IronPort-AV: E=Sophos;i="4.44,581,1249254000"; d="scan'208,217";a="175371756" Received: from unknown (HELO mal769a60aa920) ([92.24.146.134]) by out1.ip06ir2.opaltelecom.net with SMTP; 18 Oct 2009 14:49:23 +0100 Message-ID: <007201ca4ff9$cce15190$0301a8c0@mal769a60aa920> From: "mal hamilton" To: References: Date: Sun, 18 Oct 2009 14:49:22 +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-Karma: unknown: X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: AF Amps at 136 Content-Type: multipart/alternative; boundary="----=_NextPart_000_006F_01CA5002.2E41A090" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.8 required=5.0 tests=HTML_30_40,HTML_MESSAGE 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 ------=_NextPart_000_006F_01CA5002.2E41A090 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Chris=20 Do not use audio amps for RF. Build a class D or E amp and operate tr= ouble free. Audio amps were tried by some in the early days but never= worked properly.=20 Read the horror stories of yesteryears about using audio amps for RF= applications. Buckets of burnt out FETS. 73 De Mal/g3kev ----- Original Message -----=20 From: Chris=20 To: RSGB LF Group=20 Sent: Sunday, October 18, 2009 2:13 PM Subject: LF: AF Amps at 136 Hi All, Just started constructing TX for 136kHz, noticed Maplin do a Vellema= n 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 =A314.9= 9. 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 wi= th 'a few modifications'. Does anybody know where these modifications= are documented? I guess there's nothing major, reduce a few cap value= s? Remove Zobel Network etc.?? If anyone has experience with this appr= oach I would appreciate some hints. Thanks. Chris, G4AYT, Whitstable. ----------------------------------------------------------------------= -------- No virus found in this incoming message. Checked by AVG - www.avg.com=20 Version: 8.5.422 / Virus Database: 270.14.20/2443 - Release Date: 10= /17/09 13:08:00 ------=_NextPart_000_006F_01CA5002.2E41A090 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Chris
Do  not use audio amps for RF.= Build a class D=20 or E amp and operate trouble free. Audio amps were tried by some in th= e early=20 days but never worked properly.
Read the horror stories of yesteryear= s about using=20 audio amps for RF applications. Buckets of burnt out FETS.
73 De Mal/g3kev
 
----- Original Message -----
From:=20 Chris
Sent: Sunday, October 18, 200= 9 2:13=20 PM
Subject: LF: AF Amps at 136

Hi All,
Just started constructing TX for 13= 6kHz, noticed=20 Maplin do a Velleman audio PA kit that is rated at 200W (100W RMS in= to 4R). OK=20 there's no mains transformer or heat sink, but reckon it's good valu= e at=20 =A314.99. Point is the specs also say the minus 3db frequency= response is=20 3Hz / 200kHz.
The RSGB books 'LF Today' refer to= using audio=20 amps as PAs at 136 with 'a few modifications'. Does anybody know whe= re these=20 modifications are documented? I guess there's nothing major, reduce= a few cap=20 values? Remove Zobel Network etc.?? If anyone has experience with th= is=20 approach I would appreciate some hints. Thanks.
Chris, G4AYT, Whitstable.


No virus found in this incoming message.
Checked by AV= G -=20 www.avg.com
Version: 8.5.422 / Virus Database: 270.14.20/2443 -= Release=20 Date: 10/17/09 13:08:00
------=_NextPart_000_006F_01CA5002.2E41A090--