Very interesting. Evidence that you always need to measure inductance of
toroids at the operating frequency.
Vic
On Dec 21, 2011, at 10:27 PM, "Han Higasa" <higasa@plum.ocn.ne.jp> wrote:
> 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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