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Re: [Amps] Power factor and choke vs resonant-choke input supplies

To: amps@contesting.com
Subject: Re: [Amps] Power factor and choke vs resonant-choke input supplies
From: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Reply-to: g3rzp@g3rzp.wanadoo.co.uk
Date: Fri, 11 May 2007 09:39:04 +0200 (CEST)
List-post: <mailto:amps@contesting.com>
My understanding of the choke input supply is that within limits, the larger 
the choke, the better the regulation for any given bleed current, because the 
current through the choke is more constant as the load varies.. The reason for 
using an almost, but not quite, resonant choke is that it artificially looks 
like a very much bigger inductance, so a smaller bleeder is needed. If it is 
resonant, then some very high voltages appear across the choke, since the twice 
supply frequency waveform is in series with a very high impedance, so one would 
expect the voltage regulation to suffer.
Having adopted this approach, I find it works extremely well. For a LV supply, 
such as for screens, negative lead filetring and a rectifier on the filter 
gives a cheap negative bias supply....

>FYI PLASTICON CAPS have zero tolerance for over voltage.<
Not like the old papers! One of my first rigs used a WW2 8 uF paper cap rated 
at 500 v. I paid the equivalent of 5c for it, and it ran for some 18months at 
900 volts before going short circuit. For tuning chokes, I have some WW2 papers 
from radars: they're rated at 5kV and a 0.1uF is about 5 inches high, 1 inch 
thick and 1-1/2 inches wide. One heavily insulated terminal on a big white 
ceramic insulator, and one terminal on a phenolic insulator, which is why I use 
negative lead filtering.
73
Peter G3RZP
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