Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 02 Feb 2006 23:10:55 +0000
From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 02 Feb 2006 23:10:18 +0000
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Subject: Re: LF: Re: Keeping the smoke in
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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" <we0h1@msn.com>
> 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:rsgb_lf_group@blacksheep.org> 
>   Cc: LWCA LF Reflector<mailto:lowfer@lwca.org> 
>   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>
> 
>