[Amps] SB-1000 160 m power down

Vic Rosenthal k2vco.vic at gmail.com
Thu Dec 22 09:56:55 PST 2011


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 at 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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