[Amps] Henry 2k-4 HV inductor

Thu Dec 14 10:47:46 EST 2017

W8JI experienced serious fireworks doing that


----- Original Message ----- 
From: "Gary Schafer" <garyschafer at largeriver.net>
To: "'Jim Thomson'" <jim.thom at telus.net>; <amps at contesting.com>
Sent: Wednesday, December 13, 2017 2:52 PM
Subject: Re: [Amps] Henry 2k-4 HV inductor


>
>
> 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 at contesting.com] On Behalf Of Jim Thomson
>> Sent: Wednesday, December 13, 2017 12:16 PM
>> To: amps at contesting.com
>> Subject: [Amps] Henry 2k-4 HV inductor
>>
>> Date: Wed, 13 Dec 2017 05:19:53 -0600
>> From: Rob Atkinson <ranchorobbo at gmail.com>
>> To: "amps at contesting.com" <amps at 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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