Message-ID: <42494D98.8060506@wp.pl>
Date: Tue, 29 Mar 2005 14:44:08 +0200
From: Marek SQ5BPM <sq5bpm@wp.pl>
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Subject: LF: More on cores...
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Hello all,

I noticed that people are using much more turns than me in the output 
transformer, so I would appreciate any help in calculating the correct 
number of turns for the cores I am using here. Messing around the trafo 
would probably allow me to achieve more power than now (450W). Trying to 
go higher causes heavy ringing + FET heating. I've tried almost 
everything to reduce this (different combinations of Zobel network, 
decoupling, inductances in series with gates, screening, grounding 
etc.). In every case around 400W things start to go bad, 450W is a 
border of manageable heat and ringing. I am thinking about making a new 
FET driver in a way that allows regulation of the time of the FET 
on-state, leaving some rest period in-between.

Here are some details about my configuration: the power supply is 45V, 
dropping to 38-39V at around 12A (depending on the 230V mains voltage). 
I am using two R40/24/16 rings made of K2006 material, stuck together, 
for detailed info see 
http://www.kaschke.de/english/framesets/frame_ringkerne.html . After 
experimenting with different configurations, currently there's 2+2 turns 
in the primary winding, 5 or 6 turns in the secondary winding. I 
remember that 4+4 primary didn't work good, but this was just a short 
try with low power - maybe there's a way to make this work with that as 
well. Cores are slightly warm but never get hot. The power supply is 
driven through a coil made of a single core (the same type), consisting 
of 5 turns. This one gets hot only when there's too much ringing in the 
PA. Adjusting turns in this one does not change a lot.

Thanks in advance for any help, I hope to make the TX again from scratch 
this summer: bigger, better & more powerful ;)

73! Marek SQ5BPM

P.S. Don't be surprised seeing another special callsign on LF, these 
days we are celebrating 25-th anniversary of the SP5ZCC Scouts Amateur 
Radio Club. I am planning some LF operation with this call on April 
9-10th. For the time being, I hope to see some of you in the SP DX 
Contest CW/SSB on April 2nd-3rd (HF). Check 
http://www.contest.spdxc.org.pl/en/index.php for more information.