Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 02 Feb 2006 22:42:33 +0000
From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
To: rsgb lf reflector <rsgb_lf_group@blacksheep.org>
Cc: LWCA LF Reflector <lowfer@lwca.org>
Date: Thu, 02 Feb 2006 22:41:26 +0000
Message-Id: <020220062241.29124.43E28A95000E876A000071C422007358340B97010D0A020E06979D0E03@comcast.net>
Subject: LF: Keeping the smoke in
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Content-type: text/plain; charset=windows-1252; format=flowed
MIME-Version: 1.0
Content-transfer-encoding: 8bit

Hello the list,

      I've heard that the secret to keeping things going in electronics is to make sure you don't let the smoke out (that's what makes it all work apparently).

     I have again failed to do so. After rewinding my toroidal loop transformer in the ATU, I had a core overheating problem. The core is 3 stacked FT-290-77 ferrites.
After setting the Decca up on QRSS for an hour or so I noticed a problem with the rf output current, it was pulsing up and down as if the Decca guard circuit was cutting in to protect the PA. So I through the breaker and went out and opened the tuner box. Smoke poured out. Bad news. I checked the temperatures with a non-contact infra-red thermometer and the toroid core was 343 Farenheit. The Curie temperature for type 77 ferrite is 200 C (which is 392 Farenheit).  Not sure yet if the core is permanently damaged, I'm still waiting for it to cool down. 

     All credit to Laurence who managed to get a loop to work at this power level! And especially with the currents he dealt with in the parallel wire loop configuration.

    I guess I need a bigger core than the 3 stacked FT-290-77s any suggestions out there?

--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm