Thanks to all the people who have gave me advice
the 160 m power-down problems have been solved.
The cause was the second filter resonance.
I have added a second B+ filter at the cold-end of
the plate RFC. It consists of an original 0.001 uf 6 kV
ceramic capacitor C23, a troid-inductor with 14 turns
on FT-114-#43 (I thought) and a Centralab 1000 pF
capacitor.
If the values are correct the resonant freq of the filter
should be 0.69 MHz.
By inductance measurement it has been determined
that the core is not #43 but #61 and the resonant
frequency became exactly 1.8 MHz with capacitors.
That was the reason of the heat-up of C23 connected
at the cold-end of the plate RFC which introduced
the power-down at 1.8 MHz.
Now the filter consists of 3000 pF+39.8 uH +
1000 pF and the resonant freq is around 0.9 MHz.
de Han JE1BMJ
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