A tuned choke is used to enable a smaller choke to be used.
A tuned choke filter has much better dynamic regulation than a conventional
choke circuit. A conventional choke is undesirable for SSB use.
You cannot replace a tuned choke with a non tuned choke unless you go to a
very high value of choke inductance as the voltage will soar otherwise and
you will lose the dynamic regulation.
A tuned choke MUST BE TUNED TO 120 Hz at idle load current. Not above or
below 120 Hz. It requires a critical idle load current.
When tuned to 120 Hz it provides the most impedance which lowers the peak
voltage at the output of the filter system.
A tuned choke will shift slightly out of resonance when increased current is
drawn and compensate for voltage drops holding the output more constant.
The voltage rating of the tune capacitor across the choke needs to be twice
the supply voltage.
This is described in some of the Collins SSB books.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Thomson
> Sent: Wednesday, December 13, 2017 12:16 PM
> To: amps@contesting.com
> Subject: [Amps] Henry 2k-4 HV inductor
>
> Date: Wed, 13 Dec 2017 05:19:53 -0600
> From: Rob Atkinson <ranchorobbo@gmail.com>
> To: "amps@contesting.com" <amps@contesting.com>
> Subject: Re: [Amps] Henry 2k-4 HV inductor
>
> <Forget the tuned choke stuff, that's been shown to be unreliable. If
> <you want a choke input filter, get a 10 henry choke and follow it with
> <a bypass oil cap of at least 8 mfd rated for the B+ with some margin
> <over that.
>
> I have seen that Henry choke and I can tell you they are NOT 700 ma
> continuous. A real 700 ma choke made to run that current 24/7 from a
> broadcast transmitter is around 3 times the size and weight. The
> Henry choke is clearly made for low duty SSB or CW.
>
> If you want to operate any mode that has a dynamic current draw, you
> may be better off with an inrush circuit and a high capacitance filter
> of around 40 mfd. Over 50 mfd isn't necessary.
>
> If you want to operate a steady load mode like AM or RTTY, you
> probably need a continuous duty choke and not the dinky choke Henry
> used.
>
>
> 73
>
> Rob
> K5UJ
>
> ## Although the tuned choke concept works, it really is a throwback to
> the
> 1950s. IF the choke and parallel resonating cap just happen to resonate
> at 120 hz,
> the peak V across that parallel tuned choke will skyrocket, and both the
> cap and choke
> will explode. Typ the choke is resonated just a bit higher than 120
> hz, like 123 to 124 hz.
> When u start sucking loads of plate current, the inductance of the choke
> will DECREASE a bit,
> and the resonance of the choke + resonating cap combo will INCREASE
> some more, like now
> up to 124-130 hz.
>
> ### The danger lies in where the choke + cap combo happens to
> resonate below 120 hz, like say 118 hz,
> with the normal bleeder current..on RX. On TX, start drawing loads of
> current, and resonant freq increases.
> As it passes from 118 hz..through 120 hz, is when the choke and
> resonating cap will both explode.
>
> ## with a 10 H choke used instead of the oem 8H, the resonant freq
> will be a lot lower than 120 hz. As long
> as it stays below 120 hz, with full bore current drawn, it will be ok.
>
> ## I checked out a resonant choke a few years back from Dahl. It used
> the SAME hypersil C core as my dahl
> plate xfmr..and weighed identical !! IMO, resonant chokes are
> dinosaurs, toss em. The combined weight of
> a plate xfmr + mating resonant choke becomes a bunch. IMO, you are
> much better off to put the entire weight and
> $$ into the xfmr alone, then a high C filter cap on the output. You
> will end up with much better static and dynamic
> regulation.
>
> ## there are serious other issues with the obsolete resonant choke
> setup. It requires a stupid amount of bleeder power
> at all times ! On the Henry 8K, they used 5 x 100 watt at 20 K wire
> wounds, all in series. That works out to a whopping
> 300 watts of CCS diss. Thats 60 watts for each of the 100 watt rated
> bleeders = HOT. Heres the real issue. To get the
> 5400 vdc no load on the 8K, using a resonant choke setup, the required
> vac across the sec of the plate xfmr is 6000 vac.
> Henry indeed used a 6000 vac xfmr... + a FWB.
>
> ## 6000 x .9 = 5400 vdc no load...just bleeder load. Under load of
> just 1.25 A plate current, the 5400 vdc B+ drops to just
> 4800 vdc B+... or a 600 vdc drop in B+. IF any one of the 5 x 100 K
> bleeders open up, you no longer have any bleeder current
> at all. Normal bleeder current = 5400 / 100K = 54 ma. With no
> bleeder current, the HV supply now thinks its a C input.
> In order for the resonant choke to operate correctly, it requires the
> massive bleeder power at all times. With no bleeder current,
> the B+ is now 6000 x 1.414 = 8484 vdc ! Now all hell breaks loose.
>
> ## To get the same 5400 vdc can easily be done with just a plate
> xfmr, using a 3819 vac secondary + high C filter, no choke required.
> Thats using a FWB. If a FW doubler is used, then the plate xfmr only
> has to be 1910 vac. I have used both the 3818 + FWB config
> and also the 1910 + doubler config. Both work, and both offer supieor
> static and dynamic regulation vs the fubar henry radio resonant
> choke scheme. Resonant chokes only filters out the 120 hz component.
> A high C filter takes em all out.
>
> ## A xfmr with a 6000 vac sec requires the use of a lot smaller gauge
> wire on the sec winding, vs the same xfmt core, but with a
> 3819 or 1910 winding. The 3819 winding can use a lot bigger gauge wire,
> and the 1910 winding can use even bigger gauge wire.
>
> ## To answer the OPs question, since he is stuck with the oem plate
> xfmr, use the 10 H choke, toss the small resonating cap, and use
> 30-75 uf of filter cap. You will still have to use the oem bleeder
> setup, but check the condition of the oem bleeders. When you hit the
> PTT, and tubes start drawing normal idle current, that current will be
> in addition to the bleeder current. The real no load B+
> is what you have with the amp keyed, but no drive applied. We could
> care less what it is on RX.
>
> ## The resonant chokes on the various henry amps have always had issues
> over the years..and ditto with the plate xfmrs they used.
> IF you ever blow up the plate xfmr, stop right there and re- evaluate.
> I would at that point design and build a new B+ supply from scratch.
> Like a simple FWB..or FWD, and a high C filter, and a HD plate xfmr.
> Dont throw good $ after bad with silly obsolete since day 1 resonant
> or non resonant choke configs. Chokes are boat anchors. Put the
> weight into the plate xmfr..where the weight belongs.
>
> Jim VE7RF
>
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