Return-Path: Received: from rly-mg10.mx.aol.com (rly-mg10.mail.aol.com [172.20.83.116]) by air-mg10.mail.aol.com (v125.7) with ESMTP id MAILINMG101-a3a4adb2d831c; Sun, 18 Oct 2009 11:00:33 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg10.mx.aol.com (v125.7) with ESMTP id MAILRELAYINMG104-a3a4adb2d831c; Sun, 18 Oct 2009 11:00:22 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1MzXEL-0003Bl-Jm for rs_out_1@blacksheep.org; Sun, 18 Oct 2009 15:59:33 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1MzXEL-0003Bc-2q for rsgb_lf_group@blacksheep.org; Sun, 18 Oct 2009 15:59:33 +0100 Received: from out1.ip05ir2.opaltelecom.net ([62.24.128.241]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1MzXCl-0003nk-KM for rsgb_lf_group@blacksheep.org; Sun, 18 Oct 2009 15:57:56 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AsQEANfJ2kpZ8hEF/2dsb2JhbACCJy6BaIkSBskyhDEE X-IronPort-AV: E=Sophos;i="4.44,581,1249254000"; d="scan'208,217";a="28418168" Received: from unknown (HELO mal769a60aa920) ([89.242.17.5]) by out1.ip05ir2.opaltelecom.net with SMTP; 18 Oct 2009 15:59:14 +0100 Message-ID: <009d01ca5003$8f04a250$0301a8c0@mal769a60aa920> From: "mal hamilton" To: References: <007201ca4ff9$cce15190$0301a8c0@mal769a60aa920> <8FD1DC2A56674846A459F7CD0ADB7468@IBM7FFA209F07C> Date: Sun, 18 Oct 2009 15:59:14 +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: Re: Re: AF Amps at 136 Content-Type: multipart/alternative; boundary="----=_NextPart_000_009A_01CA500B.F070B120" 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_009A_01CA500B.F070B120 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I use home build on both 137 and 500 On 137 4 fets in push pull class D and on 500 1 fet in class E. Use a= LPF for each. I never had a problem with crud !!!! Reliability is good especially class E when set up properly. Use a sta= ble antenna with components adequate for the power, otherwise expect= PA smoke. mal/g3kev ----- Original Message -----=20 From: Chris=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Sunday, October 18, 2009 3:11 PM Subject: LF: Re: Re: AF Amps at 136 Thanks for your comments Mal, I did wonder if such an approach was= wise. Let's see what others have to say on the matter. I also have my= suspicions about FETs in class D and the level of crud that could res= ult. Thanks again. Chris, G4AYT. ----- Original Message -----=20 From: mal hamilton=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Sunday, October 18, 2009 2:49 PM Subject: LF: Re: AF Amps at 136 Chris=20 Do not use audio amps for RF. Build a class D or E amp and operat= e trouble free. Audio amps were tried by some in the early days but ne= ver 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 Vel= leman 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 =A3= 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 13= 6 with 'a few modifications'. Does anybody know where these modificati= ons are documented? I guess there's nothing major, reduce a few cap va= lues? 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=20 Version: 8.5.422 / Virus Database: 270.14.20/2443 - Release Date= : 10/17/09 13:08:00 ----------------------------------------------------------------------= -------- 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_009A_01CA500B.F070B120 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I use home build on both 137 and 500<= /FONT>
On 137 4 fets in push pull class D an= d on 500 1 fet=20 in class E. Use a LPF for each. I never had a problem with crud=20 !!!!
Reliability is good especially class= E when set up=20 properly. Use a stable antenna with components adequate for the power,= otherwise=20 expect PA smoke.
mal/g3kev
 
----- Original Message -----
From:=20 Chris
Sent: Sunday, October 18, 200= 9 3:11=20 PM
Subject: LF: Re: Re: AF Amps= at 136

Thanks for your comments Mal, I did= wonder if=20 such an approach was wise. Let's see what others have to say on the= matter. I=20 also have my suspicions about FETs in class D and the level of crud= that=20 could result.
Thanks again.
Chris, G4AYT.
----- Original Message -----
From:=20 mal=20 hamilton
Sent: Sunday, October 18,= 2009 2:49=20 PM
Subject: LF: Re: AF Amps at= 136

Chris
Do  not use audio amps for= RF. Build a=20 class D or E amp and operate trouble free. Audio amps were tried= by some in=20 the early days but never worked properly.
Read the horror stories of yester= years about=20 using audio amps for RF applications. Buckets of burnt out=20 FETS.
73 De Mal/g3kev
 
----- Original Message -----
From:=20 Chris
Sent: Sunday, October 18,= 2009 2:13=20 PM
Subject: LF: AF Amps at= 136

Hi All,
Just started constructing TX fo= r 136kHz,=20 noticed Maplin do a Velleman audio PA kit that is rated at 200W= (100W RMS=20 into 4R). OK there's no mains transformer or heat sink, but reck= on it's=20 good value at =A314.99. Point is the specs also say the minus=20 3db frequency response is 3Hz / 200kHz.
The RSGB books 'LF Today' refer= to using=20 audio amps as PAs at 136 with 'a few modifications'. Does anybod= y know=20 where these modifications are documented? I guess there's nothin= g major,=20 reduce a few cap values? Remove Zobel Network etc.?? If anyone= has=20 experience with this approach I would appreciate some hints.=20 Thanks.
Chris, G4AYT, Whitstable.


No virus found in this incoming message.
Checked= by AVG -=20 www.avg.com
Version: 8.5.422 / Virus Database: 270.14.20/244= 3 -=20 Release Date: 10/17/09 13:08:00


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
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