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Folks,
Does the plate load choke need to be sectioned (like interstage)?
Interstage need the primary to be sectioned to interleave the secondary, but plate load choke only has primary, if section is needed then how to ?
Follow Ups:
There is no way to use interleaving in a choke.There are however two main ways to reduce the capacitance in a choke:
1) divide it axially, in many sections in series
2) put a layer of insulating paper between each layer of copper winding
There are pros and cons for both; I believe both are used.
Edits: 12/02/23 12/02/23
Depends on how one defines a 'choke'.
Take a grid choke. Simple, single coil. You'd need two for PP...unless you snuck both coils onto a single core and then glued the T together to make the beast one single coil. Now if you wish the two ends to have better coupling to each other, I can think of a few useful interleaving options.
Assume for a moment that this PP pair is receiving balanced drive, and *NOT one side driving the other out of phase( that would be much harder to consider a choke vs a transformer).
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I needed a smaller interstage with good specifications for a new project.
Look at this response
I needed a smaller interstage with good specifications for a new project.
Look at this response
Edits: 12/12/23
It's just 80mm x 90mm X 80mm , 50H 20mA dc (max 25mA) and frequency response with a tube Ri=2K about 5Hz to 420kHz.
I case people think i not need 420kHz... This is with a load of 100k Ohm and 100pF. In case you have a coax cable of 3 Meter the capacvitive load can be easely 4 times as high and so high frequency bandwidth 4 times lower. Or just the miller capacity of the next tube will distroy your high frequency.
It depends a lot on the impedance level desired. In my (limited) experience, plain windings with no tricks are good enough for outputs below 3-4kOhms primary - usually less than 500pF.
Capacitances are very similar for higher inductances, maybe half as much, 250pF at best. For drivers which want to see 30kOhms, that's not going to do the job. You'd want a factor of 5 reduction - that's pretty difficult!
Hi Paul!
When you say, "1) divide it axially, in many sections in series "
do you mean something similar to what is in the image?
I use this technique a lot. This is just an example of a small choke with amophous core
Edits: 12/04/23
Hi, How those wires in sectioned bobbin are connected ?Just connnect them in sequence or there is a way to connect to further reduce the capacitance ?
Hi, My first attempt, I also intend to wire on Amorphous C Core for a plate load choke, few questions looking for help
(1)With an Amorphous C Core weighing 1.1kg, if I want 100H running 20mA, how many turn roughly I need to wind, and should be many many sections?
(2)Facing an issue of picking up hum, how to you shield the plate choke
Which amcc core you use?
For a good designs you need the dc current, Ri of the tube, lowest frequency you want for full 'power", maximum Vac at least.
> > Which amcc core you use?
This one AMCC from Hitachi
That's an AMCC40 and you use two (4 C ) of them.
I don't know why you want 100H but that's a lot for an anode choke. You use a tube with a high Ri i guess.
You need at least 4000 windings but without knowing further details it is not possible to give a better answer.
For the 6463 having the resistance of 3.8K, 100H at 20Hz is around 12K XL, which is 3 times of plate resistance, other tube like 6SN7 need more inductance
Ok, for a 6463 this could work although a bit more is also nice. A 6sn7 needs twice as much.
I consider in case of a swing of 110Vrms 4000 windings as a minimum. If you need more swing more windings are needed.
Hi m.mug.praedinius,
> > I consider in case of a swing of 110Vrms 4000 windings as a minimum. If you need more swing more windings are needed.
Not quite understand why you said more output voltage then more winding is needed. What factor would block the the ourltput voltage ?
I have a question
While you spend time to winfld the plate load choke, wouldn't you want to wind an interstage instead of plate load choke ？ Any constraints ?
For me I only wind 300B to 845 interstage myself because the primary only need 25H which is easier to achieve, but I have been looking the skill to wind preamp stage interstage saying primary around 100H enabling about 20mA DC, for instance 6463 or ECC99
I would always make an interstage for myself and i would also take a tube with a lower Ri to reduce the amount of windings, but, it depends also how large the swing needs to be. Other solutions are bigger cores.
Hi m.mug.praedinius,
> > I consider in case of a swing of 110Vrms 4000 windings as a minimum. If you need more swing more windings are needed.
Not quite understand why you said more output voltage then more winding is needed. What factor would block the the ourltput voltage ?
More swing means that the AC flux will be bigger. There are limitations at the magnetic field because of the pre-magnetisation and also at the maximum flux.
And with more turns you can use a bigger airgap to reduce flux
Hi m.mug,
A side issue that need your expertise
An interstage, M6 silicon steel EI76 40mm lamination, 2700T primary, 4000T secondary
When the secondary reaching around 150V rms (No DC at that moment)，the waveform seemed deformed, becoming like saw waveform(see attached photo)，what could be the cause?
Btw, it's not an interstage on the photo
Way to less information to give a reasonable answer, sorry.
In the Radiotron Designers Handbook all is explained. Just read it.How low you want to get your winding capecaty depends on how many sections you apply and how you wind every section, tight in layers or just random.
Edits: 12/04/23
And to answer your question "Does the plate load choke need to be sectioned?" YES, otherwise you have to much winding capacity. But different technique to get lower capacity
Hi,
I see your photo showing sectioned bobbin, but apart from sectioned bobbin do you have to interlave several layers of wire within one bobbin ? or No, just sequence connect each sectioned bobbins?
Yes, exactly.
There are multi-chamber bobbins available for this purpose - I believe I've seen pictures of as many as eight sections.
An RF example:
https://umiweb.com/high-voltage-winding/hv-rf-choke-1
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Ahh, Interesting. I wonder how it's done. Presumably it would require support of the open side of each section to keep it from collapsing as it's being wound. Some sort of slide on bobbin flange?
Thanks
Each seciton of the pi wound choke is also wound in a criss-cross pattern. There was a hand-cranked machine on the market in the '60s and '70s that could be used at home to wind chokes like this. Don't remember the brand now...
I remember those winding machines! A friend had one, some 50+ years ago... According to the Wikipedia article on inductors, that criss-cross winding is also called basket-weave, or honeycomb. It's another way to reduce self-capacitance. I've only seen it in RF applications and cylindrical forms, I'm not sure it remains self-supporting with rectangular bobbins.
Paul,
While on the subject of chokes, I've always wondered what it was about the design of the Magnequest "EL" chokes that made them extra linear. Was that something related to this sectioned structure?
I never got the full story, but I think there were a couple tricks to reduce capacitance. One was to add some teflon between layers, and the other was to use bifilar windings.
Many of Mike's chokes were based on the Freed archive and were designed before plastic bobbins and nylon wire insulation, so they had papers between each layer. That's not usually done these days, because the insulation on modern copper wire is much stronger and layer papers are labor-intensive. I think Mike was compensating for that difference.
!
The Mind has No Firewall~ U.S. Army War College.
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