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Author Topic: 18uH 5kV filter cap. Good or bad?  (Read 2797 times)
G3RZP
Member

Posts: 4328




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« Reply #15 on: October 20, 2012, 06:47:49 AM »

Zenki,

I do not believe that a 'tuned choke' is a 'resonant' choke. If the choke is tuned just HF of resonance, it looks like a very much bigger choke, and so a smaller bleed resistance is required for it to present critical inductance for a choke input filter. As current increases and the inductance falls, the point of resonance moves further HF, but the effective inductance is still above critical.

The difference can be as small as 0.5 Hz on a 50 Hz supply, but it makes a big difference. Actual resonance can be disastrous in terms of voltages - W8JI has told us of his experiences in this regard.

The current in the 'tuning' capacitor is not negligible, either.

There is something to be said for negative lead filtering here. For many years on a 500 volt choke input supply, I've very effectively used negative lead filtering and a 6X5 to rectify the choke volts for a bias supply. Wouldn't try it on a 2800 volt 1 amp supply, though. Too much of a coward for that!
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ZENKI
Member

Posts: 906




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« Reply #16 on: October 23, 2012, 02:36:04 AM »

Agreed 100% with your comments. Its a technique thats rarely used today and  subject that is poorly understood.  I mostly use the resonant choke technique on screen supplies  for  voltages upto 1500 volts.  It works very well to the point where you dont need a screen regulator, even on SSB.

I just wanted to make sure that  someone does not remove the  resonance tuning capacitor from the choke! Many people made this mistake on the Collins 30S1.

Zenki,

I do not believe that a 'tuned choke' is a 'resonant' choke. If the choke is tuned just HF of resonance, it looks like a very much bigger choke, and so a smaller bleed resistance is required for it to present critical inductance for a choke input filter. As current increases and the inductance falls, the point of resonance moves further HF, but the effective inductance is still above critical.

The difference can be as small as 0.5 Hz on a 50 Hz supply, but it makes a big difference. Actual resonance can be disastrous in terms of voltages - W8JI has told us of his experiences in this regard.

The current in the 'tuning' capacitor is not negligible, either.

There is something to be said for negative lead filtering here. For many years on a 500 volt choke input supply, I've very effectively used negative lead filtering and a 6X5 to rectify the choke volts for a bias supply. Wouldn't try it on a 2800 volt 1 amp supply, though. Too much of a coward for that!
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