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LF: TX-ouput transformer problems

To: [email protected]
Subject: LF: TX-ouput transformer problems
From: "Dick" <[email protected]>
Date: Sun, 9 May 2004 22:02:39 +0200
Reply-to: [email protected]
Sender: [email protected]
Hello all,

I completed my G0MRF-transmitter, and today I've done the
first tests on it.
All is working fine, except the output circuit.

As far as I can see now, the outputt-transformer on the FET's is
not good.

I'm using an old core from the HV-circuit of a computer monitor.
I got this tip from Jim, M0BMU a while ago.
Core size is about 63x39x14mm (2 "C"shaped halves, held together
with a metal spring clip)
I payed a lot off atention to have no air gap.

Used 10 turns on the primary side, centre tapped.
(That means 2 times 5 turns.......)
Secundairy coil max. 21 turns with taps, all as described in the
original design.
Well, at 15V drain voltage I already had 9Amp........
With 40V over 50 Ohm.......
FET's got hot........
I changed primairy to 2 times 7 turns instead of 2 times 5 turns,
and that gave me 15V, 5Amp with also around 40V over 50 Ohm.
So, higher efficiency......

I wonder if anyone has experience with these core's and have hints about
number of turns to be used, before I start to get into endless rewinding
coils etc.


Dick, pa4vhf

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