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=0.8 required=5.0 tests=BAYES_00,BLANK_LINES_70_80, DNS_FROM_AHBL_RHSBL,HTML_30_40,HTML_MESSAGE,NO_REAL_NAME, UNPARSEABLE_RELAY 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 u0DASuTd010676 for ; Wed, 13 Jan 2016 11:28:56 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aJIbn-0002aF-OM for rs_out_1@blacksheep.org; Wed, 13 Jan 2016 10:24:55 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aJIbn-0002a6-7g for rsgb_lf_group@blacksheep.org; Wed, 13 Jan 2016 10:24:55 +0000 Received: from omr-a020e.mx.aol.com ([204.29.186.66]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.86) (envelope-from ) id 1aJIad-0006nS-UY for rsgb_lf_group@blacksheep.org; Wed, 13 Jan 2016 10:24:54 +0000 Received: from mtaomg-mcd02.mx.aol.com (mtaomg-mcd02.mx.aol.com [172.26.223.208]) by omr-a020e.mx.aol.com (Outbound Mail Relay) with ESMTP id 3D56B3800085 for ; Wed, 13 Jan 2016 05:23:28 -0500 (EST) Received: from core-mqa05h.mail.aol.com (core-mqa05.mail.aol.com [10.74.42.15]) by mtaomg-mcd02.mx.aol.com (OMAG/Core Interface) with ESMTP id EF0B538000087 for ; Wed, 13 Jan 2016 05:23:27 -0500 (EST) Received: from 91.84.87.187 by webprd-a32.mail.aol.com (10.72.52.206) with HTTP (WebMailUI); Wed, 13 Jan 2016 05:23:27 -0500 Date: Wed, 13 Jan 2016 05:23:27 -0500 From: gw8glo@aol.co.uk To: rsgb_lf_group@blacksheep.org Message-Id: <1523a82f816-4f04-68c2@webprd-a32.mail.aol.com> In-Reply-To: MIME-Version: 1.0 X-MB-Message-Source: WebUI X-MB-Message-Type: User X-Mailer: JAS STD X-Originating-IP: [91.84.87.187] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.co.uk; s=20150623; t=1452680608; bh=IWHwAqusa74CkadiJZ+1HRQFa8z3Lgn71UItNwta5N8=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=hnAbh2JvbOOzL1NJX2k84B+iD6MygWGONAkuw/+ZpshVL6W67xr0EwKR0x5zgQl8I C6nKzLbr10bnU8RbPrZwbNCbO9RtoBb3KQR0L4VcIE17cy1NqBPqypkjbOtP7Pj+vX 8hhzAWLeougAj8bo09VfTfoaLoydB+X6naqF5aQU= x-aol-sid: 3039ac1adfd05696259f07bb X-Scan-Signature: 4999602ae0d888991d6ab5146b3aa278 Subject: Re: LF: Decca 5501 Content-Type: multipart/alternative; boundary="----=_Part_34327_228560444.1452680607762" 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: 6298 ------=_Part_34327_228560444.1452680607762 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Andy thanks for that I am looking to find a scrap amplifier module to play around with with a view to rebuild the PCB and drive circuits. Looking on a scope the switching is very symmetrical but that may be only luck. I have used pushpull fets to drive another amp I designed and it worked well using a rewound driver transformer from a pc power supply. The complete setup is now on the QRP labs website if you want to have a look, look under GW8GLO. 73 Dave -----Original Message----- From: Andy Talbot To: rsgb_lf_group Sent: Wed, 13 Jan 2016 9:51 Subject: Re: LF: Decca 5501 Bit late now, but I found the circuit of the Deca transmitter on G3XDV's website. http://homepage.ntlworld.com/mike.dennison/index/lf/decca/transmitter.htm. (Look at Fig 4, 'right' ) The driver circuit is just a single IFR520 FET switching into the transformer, so there is a net DC component - and of course it has to be a gapped core. In fact I'm a bit surprised at that circuitry, considering it has to switch the FETs alternately on each half of the output waveform, a single ended, flyback drive like that cannot possibly be symmetrical. Especially as the only reverse clamp appears to be a 68V zener.. But no doubt it is 'good enough' In my 137kHz Tx design - very loosely based on the Decca output stage, I used a ferrite transformer (ungapped) and AC coupling from the driver IC into that. Andy G4JNT On 9 January 2016 at 09:26, wrote: Thanks for the reply the transformer failed because of a small cut in the rubber sleeving where it entered the ferrite. As the ferrite is earthed the insulation on the litz was not good enough. I have a diagram and used that to help rewind the new transformer. There does not appear to be any DC component flowing in any winding according to the diagram. This unit has possibly been exposed to damp conditions as two of the input transformers were also OC primary and were rebuilt. One set of gate windings are running at the OP from the bridge and this is the one that failed. I am thinking of rebuilding the whole drive board to improve the isolation. I have already added voltage regulators to supply the ICs, this makes the 27v current a lot lower! 73 Dave -----Original Message----- From: Andy Talbot To: rsgb_lf_group Sent: Fri, 8 Jan 2016 18:53 Subject: Re: LF: Decca 5501 The fact it is a GAPPED core is of more significance than that of the type of ferrite. In a transformer application - as that appears to do - it is surprising that a gapped one is used. I do not have the circuit of the Decca transmitter to hand, but can only assume the driver has DC passing through the winding, hence the need to introduce an air gap to prevent ferrite saturation. In which case, the fact your unit overheated suggests your gap was too small and the Vt product (volt-seconds is what saturates ferrite, not current). BUT if that was the was the original unit, you need to ask the question why it should have failed before trying to replace it. Those transmitter units were very reliable under rated things, so components failing need investigating. Andy G4JNT On 8 January 2016 at 11:09, wrote: Does anybody know what ferrite grade is used on the fet driver transformer. I have had one burn out and have rebuilt it but would like to redesign it with better isolation between windings. Have tried various cores but cannot get the same clean waveform. The original is a gapped core of unknown material ferrite. Does anybody have a scrap amp unit that I can use for testing. The finished mods have given 1 kw at 53 volts, can be driven up to 75 volts but dummy load cannot take it!!! 73 Dave GW8GLO ------=_Part_34327_228560444.1452680607762 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 7bit Andy thanks for that I am looking to find a scrap amplifier module to play around with with a view to rebuild the PCB and drive circuits. Looking on a scope the switching is very symmetrical but that may be only luck. I have used pushpull fets to drive another amp I designed and it worked well using a rewound driver transformer from a pc power supply. The complete setup is now on the QRP labs website if you want to have a look, look under GW8GLO.
73 Dave



-----Original Message-----
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Wed, 13 Jan 2016 9:51
Subject: Re: LF: Decca 5501

Bit late now, but I found the circuit of the Deca transmitter on G3XDV's website. http://homepage.ntlworld.com/mike.dennison/index/lf/decca/transmitter.htm.
(Look at Fig 4, 'right' )

The driver circuit is just a single IFR520 FET switching into the transformer, so there is a net DC component - and of course it has to be a gapped core.  In fact I'm a bit surprised at that circuitry, considering it has to switch the FETs alternately on each half of the output waveform, a single ended, flyback drive like that cannot possibly be symmetrical.  Especially as the only reverse clamp appears to be a 68V zener..  But no doubt it is 'good enough'    In my 137kHz Tx design - very loosely based on the Decca output stage, I used a ferrite transformer  (ungapped)  and AC coupling from the driver IC into that.

Andy  G4JNT


On 9 January 2016 at 09:26, <gw8glo@aol.co.uk> wrote:
Thanks for the reply the transformer failed because of a small cut in the rubber sleeving where it entered the ferrite. As the ferrite is earthed the insulation on the litz was not good enough. I have a diagram and used that to help rewind the new transformer. There does not appear to be any DC component flowing in any winding according to the diagram. This unit has possibly been exposed to damp conditions as two of the input transformers were also OC primary and were rebuilt. One set of gate windings are running at the OP from the bridge and this is the one that failed. I am thinking of rebuilding the whole drive board to improve the isolation. I have already added voltage regulators to supply the ICs, this makes the 27v current a lot lower!
73 Dave



-----Original Message-----
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Fri, 8 Jan 2016 18:53
Subject: Re: LF: Decca 5501

The fact it is a GAPPED core is of more significance than that of the type of ferrite.   In a transformer application - as that appears to do - it is surprising that a gapped one is used.   I do not have the circuit of the Decca transmitter to hand, but can only assume the driver has DC passing through the winding, hence the need to introduce an air gap to prevent ferrite saturation.

In which case, the fact your unit overheated suggests your gap was too small and the Vt product (volt-seconds is what saturates ferrite, not current).   BUT if that was the was the original unit, you need to ask the question why it should have failed before trying to replace it.    Those transmitter units were very reliable under rated things, so components failing need investigating.

Andy  G4JNT

On 8 January 2016 at 11:09, <gw8glo@aol.co.uk> wrote:



Does anybody know what ferrite grade is used on the fet driver transformer. I have had one burn out and have rebuilt it but would like to redesign it with better isolation between windings. Have tried various cores but cannot get the same clean waveform. The original is a gapped core of unknown material ferrite. Does anybody have a scrap amp unit that I can use for testing. The finished mods have given 1 kw at 53 volts, can be driven up to 75 volts but dummy load cannot take it!!!
73 Dave GW8GLO


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