Re: LF: Decca 5501

To:	[email protected]
Subject:	Re: LF: Decca 5501
From:	[email protected]
Date:	Sat, 9 Jan 2016 04:26:12 -0500
Dkim-signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.co.uk; s=20150623; t=1452331572; bh=NQ44D4GWkXAPb6xoehCr10Q82XTwtlaIjKhq+BBkVPc=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=LBewq2w4I7rgaVvXoBtvAjFw7RO5Zn/q/V+abBrXshwthlOyHxLIXaOzVN0C6VqLN s/0COze33xtP/yn72BKBY0CqsSF9Et868qdBCBYvlN0Egy8GE4FO8KmovN3k6IXZku Qvf/s3G1FELOBBawWNOkkDpZt0ritVw3A3o+aeMQ=
In-reply-to:	<CAA8k23SGvY46yx8UpE72_gWJWbuEj1HMrQsg3AD6Yj9r0G=7BA@mail.gmail.com>
Reply-to:	[email protected]
Sender:	[email protected]

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 <[email protected]>
To: rsgb_lf_group <[email protected]>
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, <[email protected]> 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

<Prev in Thread]	Current Thread	[Next in Thread>
LF: T/A last Night, F1AFJ Re: LF: T/A last Night, jcraig Re: LF: T/A last Night, jcraig Re: LF: T/A last Night, F1AFJ LF: Decca 5501, gw8glo Re: LF: Decca 5501, Andy Talbot Re: LF: Decca 5501, gw8glo <= Re: LF: Decca 5501, Andy Talbot Re: LF: Decca 5501, gw8glo Re: LF: Decca 5501, Andy Talbot Re: LF: Decca 5501, gw8glo Re: LF: Decca 5501, Andy Talbot Re: LF: Decca 5501, Johan Bodin

Previous by Date:	Re: LF: XIL 137.7798 QRSS 60, F1AFJ
Next by Date:	LF: AW: XIL 137.7798 QRSS 60, markusvester
Previous by Thread:	Re: LF: Decca 5501, Andy Talbot
Next by Thread:	Re: LF: Decca 5501, Andy Talbot
Indexes:	[Date] [Thread] [Top] [All Lists]