Well, thanks all for your comments and tips.
It helped me, and I got some ideas about what
might be wrong.
I soldered out the transformer, and did some
measurements on it.
Dispite all precautions I found that apperantly the
2 core halves didn't make an ideal contact.
Pressing the two halves did gave a large difference
in inductance.........
To give you an idea, it changed from 70uH to over 130uH........
Now I have to find a creative way to put them under a
continue pressure, also when temperature changes, and
without making a short.........
I think this is the main disadvantage of using these cores.
Of course one clever guy can make an adjustable pressure
system, allowing to 'tune' the coil...........
I guess that the coil should be in resonance on 137kHz together
with the 10nF drain capacitors, which means roughly somewhere
around 126uH for each coil part.......
Hope to find some time this week to do this......but busy.....
73 Dick, pa4vhf
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