Hi Warren, an excursion to high temperature should not affect the ferrite as
this is sintered at quite high temperatures to make the ring. What might
suffer is the epoxy (usually) coating which may burn up and created a lossy
shorted turn (guess, I have no experience of this) A quick solution might be
to bung it in a beaker of cooking oil !! That will act as insulation as well
!!
Just think you could be the first station with an oil cooled antenna
transformer !!

Cheers de Alan G3NYK


----- Original Message -----
From: Warren K2ORS/WD2XGJ <[email protected]>
To: <[email protected]>
Sent: 02 February 2006 23:10
Subject: Re: LF: Re: Keeping the smoke in

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>
>
>