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Re: LF: Re: Keeping the smoke in

To: [email protected]
Subject: Re: LF: Re: Keeping the smoke in
From: Warren K2ORS/WD2XGJ <[email protected]>
Date: Thu, 02 Feb 2006 23:10:18 +0000
Delivery-date: Thu, 02 Feb 2006 23:10:55 +0000
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Hi Mike,

I don't think that the cores were damaged from the last incident. I was able to run the 250 watt transmitter through it with no problem and no measureable reflected power. I understand that Laurence also used 3 stacked FT-290-77s but actively cooled it. A cooling fan is not easy to do in my case since the tuner is in a weathertight box.
--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm

-------------- Original message ----------------------
From: "MIKE REID" <[email protected]>
What cores did Laurence use and what wire size & type? Sorry to hear she failed again. Maybe the cores got damaged the other day with no external indications like cracking or? I don't recall you having trouble with the transformer when it was dry and Teflon is way better than cotton so that leads me to think the cores were no good after the first heat cycle/failure.

Mike
WE0H

----- Original Message ----- From: Warren K2ORS/WD2XGJ To: rsgb lf reflector<mailto:[email protected]> Cc: LWCA LF Reflector<mailto:[email protected]> Sent: Thursday, February 02, 2006 4:41 PM
  Subject: LF: Keeping the smoke in


  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<http://www.w4dex.com/wd2xgj.htm>






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