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>
|
