WE Model 534-DF Ringer materials

[thx1138]

I am trying to reproduce an electrical experiment that was done in the 1940's and 1950's. In that experiment they use "phone ringer coils" as part of the circuit. The only photos are very grainy and no model numbers were given. I have acquired a Western Electric Model 534-DF Ringer and would like to know what material is used for the part to which the coils attach in that device. In the accompanying photo it is labeled "Fixed ferrous armature".

It is gray and has no rust at all. It is fairly soft and pliable - not brittle at all. I have scratched it and it has not rusted in 7 days now so it surely is not typical cast iron but it responds strongly to a magnetic field. It appears that the metal cores in the coils are made of the same material.

I need to acquire some more material to make several more armatures for the project I'm attempting to recreate. Any help will be greatly appreciated.

[unbeldi]

A 534-DF subset probably has an 8-A ringer installed.  In 1929, the 8-A was made with a 1400 ohm DC-resistance, but earlier versions only had 1000 ohms at DC.  Both versions delivered the same impedance, however.  I don't know if that makes any difference for your experiment.

I think the frame part that the coils are mounted on was called 'heel iron' by Western Electric.
I am attaching an image from a 1929 catalog for this type of ringer.
Is this what you have?  From my view it looks pretty close.  The type should be stamped on the yoke.

Since the part is a component of the magnetic circuit it would not be cast iron, but a finer ferrous alloy. Western Electric continually researched better materials and upgraded parts, so it would be necessary to determine the date of your device. This may be difficult, because not many were date-marked before 1929.

Since you are reporting that it is soft metal, I would think it is fairly pure iron.

What kind of experiment are you planning on performing?

[thx1138]

You're right. That's exactly what I have. I checked the yoke and the "8A" stamping is there. Many thanks for the parts diagram.

I found something called Permalloy today that is 80% Nickel and 20% Iron. It was developed at Bell Labs in 1914 and it has all the qualities I described above plus very low eddy currents, high magnetic permeability so it magnetizes well, and low coercivity so it doesn't hold the magnetism - exactly what is needed for its role in a ringer.

It's very similar to Mu Metal. As it turns out, it is what is used in hard disk drives today to keep the magnetism from the voice coil magnet for the actuator arm from disturbing the magnetism on the platters and heads. I have some old disk drive parts laying around and after filing off the nickel plated coating it is grey just like the parts in the ringer and has the same physical attributes, i.e. fairly soft and bendable - not brittle.

The project is a self oscillating magnetic amplifier using a WW II radar magnetron magnet, some coils, transformers, and capacitors. It looks like the problem I'm going to have now is finding a piece of Permalloy 6" X 1 1/2" X 1/8" to cover the faces of the magnetron magnet.

I saw it is/was used in transformer cores so I might be able to find it that way. I don't think I can simply weld some pieces together because the Permalloy has a very specific heat treatment regime when it is made and the welding would probably destroy the magnetic properties I need.

Thanks again for the parts diagram.

[unbeldi]

I thought that permalloy was first described in the 1920s. I have the BSTJ paper which I thought was the first publication.
I believe WECo updated some inductions coils with the material in the late 20s, but I thought that it would be too late to be in these ringers already. But as I said, perhaps the update happened without much fanfare or change in part number.


H.D. Arnold, G.W. Elmen "Permalloy, A New Magnetic Material of Very High Permeability", Bell System Technical Journal v2 1923, No. 3 p.101.

The crystal structure of Ni-Fe alloys was solved shortly after: Phys. Rev. (2), 21, (1923).

I think some receiver diaphragms were made from permalloy. These are about 2" diameter discs, but thinner than what you need, it seems. I have to check what the blades were made of that went into the 101A induction coils.

[thx1138]

I just got that info from Wikipedia so it could be unreliable - free info is kind of like free advice.

They state that it was first discovered in 1914 and in 1923 the man who discovered it, Gustav Elmen, found that its permeability could be augmented by a heat treating process. G.M. Elmen who is coauthor of the paper you cited is no doubt the same man . I remember seeing that paper in my searches but at that point I still wasn't sure that that is what I have.

Immediately after discovering the annealing process it was used in Transatlantic comms cables. I don't have any idea when it was first used in equipment but whatever was used after 1923 would probably have used it. I saw some old ringers in my searches where the frame parts are heavily rusted but I didn't pay attention to the dates. That rust wouldn't have developed on Permalloy so I'm guessing they were pre-1923. I don't think it was used commercially before that.

[unbeldi]

yup, Wikipedia editors can write anything they want without repercussions.

I searched for patents on permalloy at some time and could only come up with the same reference that is in the BSTJ article and it is a British patent dated shortly before the article. Why they would publish this in Britain is curious, perhaps to conceal the invention for a while. This perhaps also explains why they didn't put the article into Phys Rev, but in the company internal journal. It certainly was of high importance so that Phys Rev would have welcomed it.

The first transatlantic cable was put into service in 1927.  I would guess they probably used the permalloy for the repeater cores.

All this doesn't answer thought what was used in the ringers. My guess would be it was another soft iron alloy. I have not seen substantial difference in material between the late 1920 ringer frames from the late teens or early 20s. Pure iron is probably too soft to make a rigid ringer frame so it has to be hardened a little, but even small amounts of impurities have this effect.

I have also noted that the yoke is usually covered with what appears as an oxide layer, usually dense enough to cover up the stamping of the ringer model number. In order to read that, usually I have had to clean the surface with a stiff brush.  Makes me think it could be zinc-coated.

[unbeldi]

I think mu-metal pieces can also sometimes be found as shields around the radio circuits in wireless routers and such. These can be found as scrap these days.

What is the frequency or range of your amplifier project?  Do you have a working cavity magnetron?

[thx1138]

All this doesn't answer thought what was used in the ringers. My guess would be it was another soft iron alloy. I have not seen substantial difference in material between the late 1920 ringer frames from the late teens or early 20s. Pure iron is probably too soft to make a rigid ringer frame so it has to be hardened a little, but even small amounts of impurities have this effect.

Maybe an alloy of "Swedish iron"?

The reason I was thinking permalloy was because of the lack of rust. I scratched mine over a week ago and it doesn't show any sign of rust although I live in a humid climate. It's also very shiny at the scratch which could be nickel.

[unbeldi]

Don't know much anything about Swedish iron.
Now that my curiosity is raised w/r/t to the ringer frames, I will keep my senses open to such information, but have nothing much to add at this time.

The reason I was interested in permalloy was in connection with induction coils and ringer coil cores, because in the 1940s and early 50s Western Electric marked some ringers with red stripes that used a different core material which caused inductive noise problems in certain situations. I believe the material they used was a cheaper or lower quality iron variety, and that this practice started during the war.  Recently I learned that this may have started as early as 1941, which supports that idea.

[Kenton K]

Don't know much anything about Swedish iron.
Now that my curiosity is raised w/r/t to the ringer frames, I will keep my senses open to such information, but have nothing much to add at this time.

The reason I was interested in permalloy was in connection with induction coils and ringer coil cores, because in the 1940s and early 50s Western Electric marked some ringers with red stripes that used a different core material which caused inductive noise problems in certain situations. I believe the material they used was a cheaper or lower quality iron variety, and that this practice started during the war.  Recently I learned that this may have started as early as 1941, which supports that idea.

Are you talking about the stripes on the B type ringer coils?

KK

[unbeldi]

Are you talking about the stripes on the B type ringer coils?

yes
These ringers have a lower impedance than an unmarked ringer, due to the use of magnetic iron core, as stated in the BSPs.
The lower impedance causes line imbalances when used on grounded ringing circuits, and thus increases susceptibility for inductive noise pickup.