Anyone know anything about re magnetizing a C4A ringer?

[Bartonpipes]

Hello all,

All throughout this forum there are "whispers" of ways to bring back ringers that have been de magnetized by dis-assembly but after searching extensively for more information I have yet to find any.

I have read of several methods, from wrapping wire around the ringer and then hooking it up to a car battery, to an actual tool that was used to correct this condition.

My question is, has anyone actually had any success with bringing back, say a common C4A, and what methods did you use?

I have a dead one that otherwise has no problems that I would be willing to experiment on if someone could elaborate on these mysterious procedures.

-Andrew

[unbeldi]

I seriously doubt that a C-type ringer is demagnetized by disassembly. One would have to yank the magnet off the frame. The ringer frame represents a magnetic shunt, so that removing the coil should have no effect, and I have replaced broken coils, without adverse result.

What do you mean by "that otherwise has no problems"?  Do the coils have the proper resistance?

Each ringer was individually adjusted for magnetization. Off the assembly line, they came with excessive magnetization which was reduced by a tuning apparatus in which each ringer was calibrated for proper tension and performance.  IIRC, the procedure and apparatus are explained in a BLR BSTJ article.

As far as other ringers is concerned, I have left #6, or 8, or 68(?), ringers, as typically found in 534-684 type subsets, completely disassembled for months. When I finally reassembled them, they worked just like before, better actually, because the armature pivots were cleaned, lubricated and adjusted.  These numbered ringer types have a shallow U-shaped permanent magnet that is simply attached to the yoke with one screw on one end.

[unbeldi]

Just checked references...  The ringer tuning procedure is described not in BLR, but in:

Inglis, A.H.; Tuffnell, W.L; An Improved Telephone Set, Bell Sys. Tech. J.  30(2), 239 (April 1951)


The article states that proper tuning of a C-type ringer can only be accomplished by simultaneously by bending the bias spring of the clapper reed and adjusting the magnetization in small steps appropriately.

[TelePlay]

Everything I can remember reading on the forum about ringer magnetism problems dealt with the B1A ringer in the 302/5302 phones. This was a good discussion of that, one of several but maybe the best with respect to your question.

http://www.classicrotaryphones.com/forum/index.php?topic=845.0

It was started 5 years ago so I can't vouch for facts started, just providing a link to that topic.

xzzx - ringer magnetism - xzzx

[Kenton K]

C4A ringers are definitely adversely affected by disassembly. I have ruined previously working C type ringers by disassembling them.

KK

[unbeldi]

C4A ringers are definitely adversely affected by disassembly. I have ruined previously working C type ringers by disassembling them.

KK

Would you please describe your disassembly?
What did you disassemble?   Just remove the coil?

[Kenton K]

In my experience, if I remove the coil, the ringer rings, although not as loudly.
If I take of the frame (removing the shunt), the ringer doesn't work at all. 

These are just my observations-Ken

[Bartonpipes]

In my experience, if I remove the coil, the ringer rings, although not as loudly.
If I take of the frame (removing the shunt), the ringer doesn't work at all.

Yes, that has been my experience as well, and since the ringers were assembled out of raw materials and then "tuned" there must be some way to get a demagnetized ringer to work again.

What I wouldn't give to go back in time and snatch some tools from the Western Electric factory...

-Andrew

[unbeldi]

Well, you can read about that in the article I cited. There is a drawing of the apparatus.
But essentially you need two magnets lined up axially on both sides with the ringer magnet to produce a strong field aligned properly in direction with the existing field of the ringer magnet. There is no room to wrap any coils or wire around that.  The ringer coils have far too large an electrical resistance to be useful for magnetization, but perhaps you can drive them to the limit before DC break down with perhaps 300 V. That's a current of about 50 mA, 10 times as much as during AC ringing.
The demagnetizing steps for tuning can be achieved with a reverse field by switching polarity.

The performance of the ringer however, is a delicate balance between the magnetic properties and the mechanical tension of the reed. That is the hard part to accomplish without the automated tuning system in the factory. The machine they used automatically determined and performed the proper bending of the bias spring by monitoring the mechanical vibration of the clapper with a phone diode, while adjusting the magnetization of the magnet.

I suspect that the failures reported are mainly due to disturbance of this balance by removing the magnet or clapper, something I would never attempt knowing how they are adjusted in the first place.

[Dennis Markham]

In 2009 there was some discussion here on the Forum about the loss of magnetism to a C4A ringer when disassembled.  JorgeAmely did some research and experimentation after he read an I.T.&T. document about the topic.  I initiated this topic and a pdf of Jorge's information is attached to my opening comment.  It can be seen here:

http://www.classicrotaryphones.com/forum/index.php?topic=845.15

Perhaps Jorge will weigh in on this topic again and cite the I.T.&T. document I referenced.

~Dennis

[unbeldi]

In 2009 there was some discussion here on the Forum about the loss of magnetism to a C4A ringer when disassembled.  JorgeAmely did some research and experimentation after he read an I.T.&T. document about the topic.  I initiated this topic and a pdf of Jorge's information is attached to my opening comment.  It can be seen here:

http://www.classicrotaryphones.com/forum/index.php?topic=845.15

Perhaps Jorge will weigh in on this topic again and cite the I.T.&T. document I referenced.

~Dennis

I did find the document last night and read about the measurements.  However, there was no discussion about the error bars on those measurements and the perceived decrease was only in the ten to twenty percent range.

I still haven't found the ITT document that is mentioned. Title, date, location?

[Bill]

As Unbeldi notes, the referenced BSTJ article refers to type C ringers. When comparing the new phone design (500) to the old design (302), the article states that "Instead of the usual U-shaped magnet, the new ringer employs a small cylindrical magnet of ALNICO V, which results in considerably higher permanent magnet flux". I read this to say that ALNICO V magnet in the Type-C ringer will retain its magnetism much better than the old soft iron magnets in the Type B ringers. This would account for the observation that disassembling a B-type ringer can be disastrous, while C-type ringers are more forgiving. Note that I have not done either.

The referenced ITT document may be this one
http://www.telephonetribute.com/pdf/itt240.pdf

Finally, remagnetizng an ALNICO V magnet can be done in a home brew fashion by using rare-earth (usually neodymium) magnets in a home brew jig. See, for example,
http://www.mojotone.com/support/kb-pickup-parts/How-do-I-magnetize-alnico-pickup-magnets
While this is appropriate for some magnet applications, and does have a crudely-adjustable remagnetizing strength, I seriously doubt that it can be done with the required precision for a C-type ringer. Again, please note that I have not tried this.

Bill

[unbeldi]

Thanks for the link to the ITT document.  This is probably the most extensive ringer servicing paper I have seen and details the intricate relationships between type of ringer, frequency of ringing, signal voltage, and circuit design (capacitor value).

Kellogg has always been the leader in ringer design knowledge, and frequency ringing in particular, I feel.  They were the first to recognize Western Electrics poor harmonic ringer design and improved the state of the art.
The poor design concept of WECo's harmonic system may have led them to abandon frequency ringing and instead focus on other selective signaling systems.  However, the economics of scale of the Bell System may have favored WECo's approach, as the cost of accurately maintaining frequency ringers in large scales may have been more costly. This is perhaps in analogy to the integrated network design that Kellogg and others pioneered, but simply were not competitive in cost with simpler wiring schemes.

[Kenton K]

I have observed that disassembling C ringers is more destructive than disassembling B ringers. B ringers will still work, although not as well, after re-assembly.
I think the article you cited is referencing the strength of the magnet, which is why c type magnets can be much smaller.
I also believe B type ringers are more forgiving because the overall mechanism. As I observe, B type ringers have a "push" "pull" action.
On C ringers, the armature is in a very specific equilibrium. With a every voltage cycle, the pulling magnetic force on one side of the armature turns off. The magnetic force is left to pull the clapper against the pull of the bias spring. As opposed to B type ringers, the magnet is needed to maintain an specific magnetic strength in order for the ringer to work.

Just what I believe is going on. Please correct me if I'm wrong.
kk
KK

[Dennis Markham]

I'm not sure (don't know) if the document posted by Bill is the one I recall JorgeAmely reference some time ago.  I will contact him to see if he still has that document available.