[JohanBee]

If you changed everything around, go for the coil. It has probably lost its Q somehow.
I had the same problem on the next highest band in my Trio 9R59D. As last thing I did, I took out the coil and warmed and soaked off the remaning wax coating and bruched it with polypropyl alcohol.
It solved the problem. On the highest band I had to take off the winding and clean the former and rewind it with new wire, as the wax was stuck between the turns of the thicker wire, to make it work properly.
It’s not many turns on these higher frequencies, but count the turns and double check the total length of the unwinded wire. The tap seen in the diagram, can be the form of a link between the turns of the main coil or a soldered tap.

I think the Q-value of the coil is most important at the low end of the bands when the parallell capacitance is largest.
My oscillators were also fluttering when working higher up in frequency with less capacitance, due to the low Q. All caused by the Q-destroying wax coating.
There may also be some other resin coatings than wax that will deteriorate the Q by age.


I’m also thinking of that 10K anode resistor you changed. It maybe also had some self-inductance to help deload the oscillator at higher frequencies. Could be tested with a small inductance of arond 100uH in series with it.

Also see my thread on the 9R59 in this same section of the forum.