The choke needs to be resonant at 120 Hz with only bleeder current, not
higher in frequency. Yes there are very high voltages across the choke at
resonance. You need a very good cap and voltage capable choke.
When you draw more current from the supply the choke inductance drops and
the resonance point shifts higher in frequency.
If the choke was not resonant with low current there would be no need for
it.
Peak power line and transformer current will be much lower with the choke
than without.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Jim Thomson
> Sent: Monday, April 04, 2011 6:18 AM
> To: amps@contesting.com
> Subject: [Amps] Alpha vs. Henry
> Importance: High
>
> Date: Sun, 3 Apr 2011 21:00:39 -0400
> From: "Gary Schafer" <garyschafer@comcast.net>
> Subject: Re: [Amps] Alpha vs. Henry
>
>
> Not according to Collins. They say that the choke should be resonant at
> 120
> Hz with minimum critical current, eg bleeder current, which keeps
> voltage
> from soaring.
>
> As current draw increases the inductance of the choke will drop, going
> out
> of resonance and increasing ripple voltage out of the supply.
>
> 73
> Gary K4FMX
>
> && resonant chokes schemes are steam engine technology..and buy you
> absolutely ..nothing !
> Resonate the choke at 120 hz... and the peak V across both the choke
> and the resonating cap will be
> through the stratosphere. Both will blow up, the choke will be
> ruined, and the cap will explode.
>
> && To build em correctly, you have to suck one helluva lot of bleeder
> current. At that point, the choke should
> be resonant ABOVE 120 hz. OK... now when you suck loads of plate
> current, the choke L will drop a bit...and
> resonance will INCREASE. IF the coke resonates BELOW 120 hz...with
> just bleeder current... you are in trbl.
> When sucking plate current, the resonance will increase, and when it
> passes through 120 hz....Kaboom every time.
>
> && It`s a stupid flawed design anyway, imo. The 8 k ultra runs
> 5400vdc NO load. To pull this off, they use a
> 6000 vac plate xfmr. .9 x 6000 = 5400 vdc no load...except for the 5 x
> 20k at 100 watt ccs wirewounds..all in
> series. That`s 300 W CCS of bleeder..which is a blast furnace !
> Each 100w resistor is dissipating 60 w...and they
> run extremely hot. OK, now if just any ONE of those bleeders ever
> open`s up... watch out. The B+ will soar to
> 1.414 x 6000 = 8500 vdc. At that point those failure prone oil caps
> used in the henry amps will become IED`s.
> The tube may well be next, along with bypass caps, and everything else
> you can think of.
>
> && The regulation on the 8k is nothing to brag about either. 4800 vdc
> with just 1.25 A of plate current. That`s a 12 %
> drop.. It drops 800+ vdc So much for the good regulation. Both
> the plate xfmr and the mating choke are best seller`s when
> dahl was still in business.
>
> && Here henry used a 6000 vac xfmr....when a 3800 vac xfmr + FWB
> would have worked a helluva lot better.
> Even a 1900 vac xfmr and a FWD would have worked better. A 6000 vac
> xfmr is a poor utilization of it`s
> winding. Then toss in the huge,heavy choke + heavy oil caps. The
> classic resonant choke setup only filters 120 hz to boot. It won`t
> reduce the ripple at 240,360,480 hz. So they still need a mess of oil
> caps.
>
> &&& A simple 3800 vac hypersil xfmr, or similar... + a BIG C filter
> will run rings around the resonant choke scheme. Why
> spend $$$ on plate xfmrs with massive oversized sec V ratings =
> smaller ga wire used= low current capability....then toss in the
> meagbuck heavy choke = 1921 technology.
>
> later... Jim VE7RF
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