US Military Spec. Chokes

[reinw33]

Hello everyone,
Below chokes and Transformers were used in a RA-133 preamp with tubes IIRC OD3 tubes.
Are those chokes gapped?
I would like to use them in a mic preamp as ripple filter chokes but don't know. Have to guess.
I don't know much about historic american tube gear for military.
Any comments are appreciated.
Thanks.

 

[reinw33]

 

[reinw33]

 

[reinw33]

Hefty 32H at over 1kg each.
It fits into a 3RU chassis.
Monsters.

 

[trobbins]

What's not to know? They re just chokes and a transformer, and luckily with ratings and a schematic to help you. If anything you should confirm the insulation resistance at 1kV, and DCR levels. The 5.8V heater rating may be a loaded voltage - perhaps best to test the heater voltage at nominal mains voltage, as if it is down at 5.8V then you may have issues with your application. The chokes were designed for CLC filter application (ie not choke input filtering). Yes the chokes would be gapped - that is how a choke is designed for that spec of 48mAdc.

 

[CJ]

OT: a choke tidbit that will expand your brain>

http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol3_025.html

 

[reinw33]

What's not to know?...

Basically everything about those inductors only.
I don't own those in the picture.
This is all I have so far.

In the image it's just the ugly laminations with bents from the welding points about 600g.
Scrap Transformer laminations almost 3kgs.
I would use the bent ones for chokes and the straight ones for an output transformer.
I wanted to use all of those for Neve 1166 OTP variation with EI95. @CJ posted the specs for that one, kudos to him for that.
But I now realize, I'm short on money to spend for DIY projects and might have to wind myself.
Pretty likely actually. Because I want to achieve a build as cheaply as possible to see what is possible.
I wished all of the lost images of unwindings of transformers from @CJ jsut were still here to DIY.
I looked up as many as possible of those, but several are gone and the schematics not available anylonger.
Does some have a collection of @CJ Tx disassemblies and unwindings and can help out with a dropbox link or similiar?
Thanks.

EDIT: So if I don't end up with those filter chokes, I'll have to wind but I really don't want to use absolutely new wire for this, because I would use varnish anyways and for that older wire should be good enough but I don't have that yet.

 

[reinw33]

OT: a choke tidbit that will expand your brain>

http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol3_025.html

Hi @CJ,
yeah I was familiar with this before.
Thank you.
It's a very nice pigeons eye overview so to speak.
I did read it before and also the ebook.
It's really handy.
Thanks for your help @CJ.

 

[reinw33]

This was a nice workout.
The lams are all straight now.

Does somebody here just buy big chokes for whatever one needs in a project?
It's a whole different ball game when you need to come up with the design and eventual part on your own,
I have to wind my own chokes, I couldn't find modern commercial psu chokes with enough inductance.
And I feel much better about DIYing it than buy old stuff and find out. To hope it's right for the job or that it still works.
And the upside is, you do get some work out out of it.
So I am looking for more copper wire now.
It's a slow process and a longterm project.
Thanks.

 

[trobbins]

While you are looking for more wire, have you estimated the typical parameters that would give you the inductance at the dc mA you are after, and do you have a measurement tool to determine inductance at a level of dc mA ?

 

[Walter66]

As far as I know, when they are used single ended as chokes, they naturally have a gap in the core. Lundahl chokes have different air gaps for different idle currents. Study his choke datasheets for comparison. They can be used for the PSU of a preamp, data and schemo how to use them are attached to your postings.

 

[reinw33]

While you are looking for more wire, have you estimated the typical parameters that would give you the inductance at the dc mA you are after, and do you have a measurement tool to determine inductance at a level of dc mA ?

Steel type is unknown, AL needs to be measured yet.
About to do that.
So yes and no, I do have an oscilloscope but not a pulse tracer.
After that Inductance should come out sufficient.
I'll just adjust the gap to suit the current needs of the circuit.
What I think about is how to shield and pott it, that I like dealing with longterm.
And I have an idea what I like but not how to seal it tight.

 

[reinw33]

As far as I know, when they are used single ended as chokes, they naturally have a gap in the core. Lundahl chokes have different air gaps for different idle currents. Study his choke datasheets for comparison. They can be used for the PSU of a preamp, data and schemo how to use them are attached to your postings.

Thanks for the comparison.
I definitely compare to Lundahl on paper, but it's right now to expensive for me. It's about 130€ here.

 

[reinw33]

@trobbins
I do want it to be pottet.
Not according to american military spec, it can be less than that ofcourse. But even below that, I have to like the process and materials and is difficult to achieve that, even when I think about it.

 

[reinw33]

I put some turns on it and measured inductance and calculated it seemed to confirm the typical range of values for AL for EI95.
Planning with the 31 awg/swg 0.3mm wire and around 4000 turns on it would have only around 5-6.4ish H inductance.
That's not enough at all, I need at least 15,2H.
0.3mm wire 4000 turns with that core doesn't seem to make it, to 50% of needed inductance.
I'm kind of torn between a bigger core, perhaps double the size, or a smaller wire that is probably much less nice to wind that many turns.
Even assuming max possible AL, I don even get above 13H with 0.3 mm in theory.
Stick to 0.3mm and try a bigger core?

 

[reinw33]

EDIT: My inductance test probably had way too few turns on it.
That's why it came out so low in inductance on paper in theory.
I feel like it should have quite more inductance with that many turns on it on a 600g core.
I will try another test with windings in the hundreds of turns to get a more accurate AL value.

 

[trobbins]

How are you measuring inductance ?

 

[reinw33]

How are you measuring inductance ?

I have at least two ways.
Digitally and analog.
I have done both.
I did test digitally here, on the quick.
This is very interesting.
When I use the tested AI value, I need 6700 turns for 15,2H.
This seems much and given that I used very few turns I think that number could improve to lower turns in total had I tested with more turns but that's is more hard work.
Calculating with permeability of 1000-6000 of that EI95, I go from 3H to 120H with 6000².
This is so ridiculous.
Because that imputes a permeabillity of around 150-6000 of steel. I can't believe that either.
But when I give it a thousand permeabillity, it needs less turns ofcourse.
Which is in line with my suspission that more hard work was needed with more turns in testing AL.
There's s the permeabillity complexity that makes you mess up so easily, so far off, it's insane.
I have never liked that permeability formula, ever.
So I really tend believe the tested AL value of 332.
it might get to 400 with more turns and proper bobbin and a bigger core even higher.
EDIT: Have to take a break from this, my first big choke shouldn't take 6700 turns, I shouldn't be in too bad shape with 0.3mm wire.
If the permeabillity is 1k, 3k turns might give 25H. It's just my first big filter choke. It's yet very gambly early on.

 

[reinw33]

Thanks for all the replies.
Decided to use 31 swg that I have at hand for the first filter choke.
With some adjustments should turn out fantastic.
Stopped looking for wire. Received great offer for same 31 swg tho.

Open for ideas for potting DIY chokes.
I have cheap ideas in mind. I can then always repott into a more proper container when available.