Hello,
You'll all remember the problems I had to get this "thing" running.
I did do some modifications as described by Jim, M0BMU:
-I took out C23, 470nF
-Inductor L4 (was 11 turns on a T94-2 core) changed to
about 28turns 1.25mm wire on a T106-26 core.
This is a white-yellow core often found in computer powersupplies.
-C22 and C24 (was 10nF each) were replaced by a serie combination of
an 4700pF C and 5 Ohm/10 Watt resistor (2 x 10 Ohm/5W in parallel)
The output transformer is 8 turns 1.5mm wire bifilair as primairy coil, and
the
secundary ouput coil is wound over it consisting of 25 turns 1mm wire, from
which
5 turns are actually not on top of the primairy.......
I didn't write down the exact value of the coil but it was somewhere in the
400-500uH region.
TEST RESULTS on 50 Volt......
FET: 2 times IRFP260N
Voltage measured after the current measure resistors (so at the point
L4/C25-26)
was 50.1Volt at key down.
Measured draincurrent: 11.6A
DC-input: 580 Watt.
Measured output: 560Watt at 50 Ohm!
Efficiency: 96 procent!!
The only things that gets hot are the current measurement
resistors...........
Also some heat created in the 4700pF/5 Ohm circuit.
and off course my 500Watt dummyload, which doesn't like so much
power........
Meanwhile I put a fan on the current resistors (R25, R26) to keep them
cool.........
I also found another error in the schematic diagram: R11 and R34 (was 12k)
changed to
560Ohm-820Ohm.
Once again thanks to all who helped me with usefull information.
Next step will be working on loading coils and so on, while testing the
transmitter
on long duration transmissions. Need to put some extra cooling on my already
forced air cooled dummy load..........
73, Dick, pa4vhf
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