Return-Path: Received: (qmail 3744 invoked from network); 11 Nov 2002 12:07:42 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 11 Nov 2002 12:07:42 -0000 Received: (qmail 4279 invoked from network); 11 Nov 2002 12:07:07 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 11 Nov 2002 12:07:07 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 18BDKQ-0005ve-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 11 Nov 2002 12:06:06 +0000 Received: from [213.218.77.53] (helo=cmailENV1.svr.pol.co.uk) by post.thorcom.com with esmtp (Exim 4.10) id 18BDKP-0005vV-00 for rsgb_lf_group@blacksheep.org; Mon, 11 Nov 2002 12:06:05 +0000 Received: from [62.21.133.49] (helo=w8k3f0.freeler.nl) by cmailENV1.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 18BDKN-0000hp-00 for rsgb_lf_group@blacksheep.org; Mon, 11 Nov 2002 12:06:04 +0000 Message-ID: <5.1.0.14.0.20021111125625.00a65af0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Mon, 11 Nov 2002 13:06:42 +0100 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <5.1.0.14.0.20021110135548.00a91d88@gemini.herts.ac.uk> References: <057f01c2875f$0fd4ea90$0101a8c0@athlon> <5.1.0.14.0.20021108112020.00aeef28@gemini.herts.ac.uk> MIME-Version: 1.0 Subject: Re: LF: To Ponder over the weekend Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=-1.8 required=5.0tests=BIG_FONT,EMAIL_ATTRIBUTION,IN_REP_TO,REFERENCES, SPAM_PHRASE_00_01version=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Content-transfer-encoding: 8bit To All from PA0SE:

Jim, M0BMU wrote:

The un-neat thing about an oil dielectric is its propensity for catching fire... also, I don't think it has particularly low loss at RF - although a lot of big TX capacitors are oil-filled, the oil is there to increase the breakdown voltage, rather than act as the main dielectric, which is usually mica, I believe.

The wave form of the output voltage of my 136kHz transmitter with four HEXFET's type IRF520 in parallel-pushpull was not quite sinusoidal. To absorb the harmonics I connected a capacitor of about 50nF over the primary winding of the output transformer. I tried capacitors of different type and make but all became hot after a while.
The only one running cool was a white coloured 50nF capacitor of a type that can be frequently found in German WW II radio equipment. These capacitors are oil-filled....

73, Dick, PA0SE