[Amps] Henry 2k-4 HV inductor

Jim Thomson jim.thom at telus.net
Wed Dec 13 13:15:56 EST 2017

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



##  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

##  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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