Return-Path: Received: (qmail 70563 invoked from network); 1 Apr 2005 18:33:27 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore03.plus.net with SMTP; 1 Apr 2005 18:33:27 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1DHQxw-0001u6-Um for dave@picks.force9.co.uk; Fri, 01 Apr 2005 19:33:56 +0100 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1DHQxw-0001u3-S5 for dave@picks.force9.co.uk; Fri, 01 Apr 2005 19:33:56 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1DHQxT-000Brh-EJ for dave@picks.force9.co.uk; Fri, 01 Apr 2005 18:33:27 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1DHQxE-0005RC-9O for rs_out_1@blacksheep.org; Fri, 01 Apr 2005 19:33:12 +0100 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1DHQxD-0005R3-MO for rsgb_lf_group@blacksheep.org; Fri, 01 Apr 2005 19:33:11 +0100 Received: from smtp807.mail.ukl.yahoo.com ([217.12.12.197]) by relay.thorcom.net with smtp (Exim 4.43) id 1DHQxB-0000zA-UP for rsgb_lf_group@blacksheep.org; Fri, 01 Apr 2005 19:33:11 +0100 Received: from unknown (HELO aquarids) (ganymede444@217.42.194.93 with login) by smtp807.mail.ukl.yahoo.com with SMTP; 1 Apr 2005 18:33:03 -0000 From: "Dave G3WCB" To: rsgb_lf_group@blacksheep.org Date: Fri, 1 Apr 2005 19:33:08 +0100 Message-ID: MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2911.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 Importance: Normal In-Reply-To: <000201c536cf$63eaf580$3ae8fc3e@l8p8y6> X-SPF-Result: relay.thorcom.net: 217.12.12.197 is neither permitted nor denied by domain of btopenworld.com X-Spam-Score: 0.5 (/) X-Spam-Report: autolearn=no,FROM_ENDS_IN_NUMS=0.516,HTML_60_70=0.027,HTML_MESSAGE=0.001 Subject: LF: TX Cores Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.5 required=5.0 tests=FROM_ENDS_IN_NUMS,HTML_40_50, HTML_FONTCOLOR_BLUE,HTML_FONTCOLOR_UNKNOWN,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-Spam-Filtered: by PlusNet SpamCORE (v3.00) Content-transfer-encoding: 8bit
Dear Mal, LF group.
 
If your looking for inspiration regarding Big PAs, you should take a look at G4FTC's amplifier pages.
 
http://www.qsl.net/g4ftc/amplifiers/136khz/home.htm
 
http://www.qsl.net/g4ftc/amplifiers/decca/home.htm
 
One of these big amps uses a bridge configuration, like the Decca PA. It seems to have some advantages....and you can run it straight form 250v mains!
 
73,
 
Dave G3WCB
(150w only...)
 
 
 
-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of hamilton mal
Sent: 01 April 2005 14:25
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: RE: TX Cores

 
----- Original Message -----
Sent: Friday, April 01, 2005 10:07 AM
Subject: LF: RE: TX Cores

Dear Mal, LF Group,

 

No – it is possible to design these transformers with a small air gap, but there does not appear to be a great advantage to doing so because the required number of turns increases, increasing the “copper” losses and offsetting any reduction in core loss. There is always a quite large gap in the original LOPT – often this is produced by inserting plastic film spacers between the core halves. These, and any glue, should be removed so that the core halves fit together perfectly. Sometimes the gap is produced by machining the core legs to unequal lengths, in which case you can’t really use the core in this application.

 

Cheers, Jim Moritz

73 de M0BMU

 

Tnx Jim for the info. My LOPT cores have equal leg length, and in the past I have removed the plastic spacers when present and they work well. This appears to be what u have done ie no gap.

Thanks to all the others as well for their info.

I am working on the project at present. I notice up to a few hundred watts there never seems to be a problem with heat, explosions etc but when aiming for an o/put of 1 kw things are more critical, 2 cores needed, more robust wire on the transformer. My present project uses 2 x 26A/500V Fets  on each leg ie total 4. I am hoping to get up to about 100v and see what happens. So far I have managed 800w out at 40v/22amps but above this things get tricky, pa getting hot and the winding on the o/p transformer getting warm. The design is similar to YXM/MRF with a few refinements.

I happen to have these fets so I am trying them out, lets hope they survive !!!!!!!!

All suggestions welcome. In the past I have used low voltage high current up to 60Amps and all has been well but going to a higher voltage and lower current the PA performs differently even though this would appear a better approach, using the above Fets.

I should really use my Decca and save myself a lot of trouble with home built gear, but then there is not the same satisfaction when working the DX !!!!!!

73 De Mal/G3KEV

 

 

 

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of hamilton mal
Sent: 31 March 2005 13:36
To: rsgb_lf_group@blacksheep.org
Subject: LF: TX Cores

 

Hi All Jim M0BMU.

Jim ur mod to the G0MRF using a TV line output transformer. Did u leave a gap between the cores or not ?

73 de Mal/G3KEV