Modern Networks, Subsets and other related components

[Alex G. Bell]

When the 425 network (first the 425A whose circuit is quite different) and soon after the 425B were developed, encapsulating the network in a viscous fluid was the best way to make it extremely immune to damage from impacts such as dropping the phone and to exclude moisture which in the long run would cause the paper dielectric capacitors to absorb moisture and become electrically leaky (allow small amounts of DC current to pass through).  Printed circuits did not even exist.  So the metal can with potting compound was the best way to produce a mechanically and electrically robust component.

Later WECo networks such as the 4228 and 4293, designed when well-sealed plastic film dielectric capacitors had come along, did away with the canister and potting, using the terminal plate as the "substrate".  The non-Bell System printed circuit versions also became possible due to the advent of printed circuit boards and improvements in capacitor technology.

Ralph Meyer's books go into great detail about the evolution of speech circuit induction coils and networks.  I recommend them highly for anyone who is interested in this and many other aspects of telephone set circuit design and operation.

Of course there are later telephone sets with completely electronic speech circuits using ICs or transistor circuits but the ITT, S-C and NECo/Northern Telecom/Nortel PC networks which contain a laminated core transformer are 425B close derivatives with no major conceptual changes.

IIRC, Meyer may also have said that even the AE 80-type self-compensating networks are 425B derivatives to a considerable extent.  I'd have to review the book to be sure whether he said this or not.

[HarrySmith]

It looks the same as the 500. Switch hook, dial mount, ringer all are the same. Looks like you could pull out the PC board and drop in a 425 net.

[Alex G. Bell]

It looks the same as the 500. Switch hook, dial mount, ringer all are the same. Looks like you could pull out the PC board and drop in a 425 net.

You could.  The plastic bracket onto which the PCB snaps mounts on the same hole centers as a 425B or the original ITT metal can version.  You would have to drill or press the rivets out. 

But a network intended for a rotary dial with the internal capacitor connected to the F terminal would not be compatible with certain tone dial versions.

[twocvbloke]

I've a Cortelco 2554 myself and aside from a slight "cheapened" feel to it, over all it feels a lot better than some of the chinese tat sold as vintage-style phones, so I wouldn't dismiss Cortelco phones as being pretend phones, they're as close to the originals as you can get today...

[RotarDad]

Alex - Thanks again for the clear, detailed reply.  I always learn something on this forum!

TwoCV - I agree that the Cortelco 2500 is still a nice piece of vintage telephony.  This particular one looks NOS as well.  Always nice in black.

[Alex G. Bell]

Alex - Thanks again for the clear, detailed reply.  I always learn something on this forum!

TwoCV - I agree that the Cortelco 2500 is still a nice piece of vintage telephony.  This particular one looks NOS as well.  Always nice in black.

You're welcome. 

I agree in general except that this phone contains the ball bearing ringer I mentioned elsewhere.  The ball bearing ringer is best described as an "ingenious piece of cheap garbage".  Ingenious in that it works at all.  Instead of a hinged armature the ball bearing is alternately attracted to two pole pieces, running back and forth along a raceway to strike the gongs. 

Cheap garbage in that it has no bias spring so it taps if connected to a line with rotary dial phones.  The plastic frame is so weak that if the phone is dropped the frame may break and not work at all.  I've seen the aftermath of this first hand.

I agree though that with a metal baseplate, conventional handset and internal spade tipped connections it feels a lot better and is more maintainable than most of the "disposable" phones with all soldered connections that are out there.

[twocvbloke]

Yeah, my 2554 has the ball bearing chucker ringer, and it is odd sounding compared to other ringers, even the cheap chinese things inside the tat phones, I also have one inside a Geemarc "Mayfair" GPO 746-lookalike phone that has the 2-gong version but cheapened even moreso than Cortelco's design:

http://www.classicrotaryphones.com/forum/index.php?topic=11573.msg123522#msg123522

The worst part being that the gongs in that phone are barely different in tone so it just sounds wrong in every possible way...

[Alex G. Bell]

Yeah, my 2554 has the ball bearing chucker ringer, and it is odd sounding compared to other ringers, even the cheap chinese things inside the tat phones, I also have one inside a Geemarc "Mayfair" GPO 746-lookalike phone that has the 2-gong version but cheapened even moreso than Cortelco's design:

http://www.classicrotaryphones.com/forum/index.php?topic=11573.msg123522#msg123522

The worst part being that the gongs in that phone are barely different in tone so it just sounds wrong in every possible way...

A major accomplishment at that: not just in some ways!

534 and 634 subsets had two gongs of the same pitch.  This effectively doubles the apparent strike rate, giving the ringer (at least to my ear) a more frenetic, urgent and slightly annoying sound quality.  584 and 684 subsets and everything after instead have the more pleasant warbling quality of two different gongs.

[RotarDad]

Alex - I was re-reading your network post here, and I have a question.  The later 4228 network was still housed in a box, despite not needing the potting to protect the capacitors from moisture.  Was this done to simply to protect the components during manufacturing, and later service of the phone?  I guess the box also provides a nice mounting for all of the screw terminals as well.  Thanks!

[Alex G. Bell]

Alex - I was re-reading your network post here, and I have a question.  The later 4228 network was still housed in a box, despite not needing the potting to protect the capacitors from moisture.  Was this done to simply to protect the components during manufacturing, and later service of the phone?  I guess the box also provides a nice mounting for all of the screw terminals as well.  Thanks!

The 4228 was made in many versions with different mounting arrangements, with and without the rotary dial filter capacitor and ringer capacitor but AFAIK none of them have a metal housing.  The ones I'm aware of have an open bottom with a molded capacitor block and the induction coil both connected into the terminal plate from below, pins facing upward.  I think you must have some other network in mind.  What telephone set did you see it in?

[RotarDad]

Alex - You're probably right.  I restored a payphone some years back, and removed a 4228 net from it.  I do remember the net had screw tabs at each end, but likely my memory of other aspects is fuzzy.  That net was sold with some other parts so I can't take another look.  You mention several versions;  I probably had one with a mounting frame of some type, not a box.  Sorry for the tangent here...

[Alex G. Bell]

Alex - You're probably right.  I restored a payphone some years back, and removed a 4228 net from it.  I do remember the net had screw tabs at each end, but likely my memory of other aspects is fuzzy.  That net was sold with some other parts so I can't take another look.  You mention several versions;  I probably had one with a mounting frame of some type, not a box.  Sorry for the tangent here...

No problem. 

I don't know of any payphones factory equipped with 4228 nets.  The ones I know of had 4010s in the upper housing, the same small net probably developed for use in 702/1702/2702 Princess sets to make space for an internal ringer.  4010s did have a metal can, but they go a long way back, to the 1960s I'd guess. 

It's possible some payphones originally made with the 4010 used the 4228 in later production but if so I've never seen it.

[RotarDad]

Alex - To clarify, the payphone had many issues, including the incorrect 4228 net.  I did fully restore it back to correct 236G config, which does indeed have a 4010 Princess-style net mounted behind the coin track.  To salvage some value from my wayward inquiry, here are some nice pics of a 4228 (no mounting tabs that I see) from beatriceco.com:

[Alex G. Bell]

Alex - To clarify, the payphone had many issues, including the incorrect 4228 net.  I did fully restore it back to correct 236G config, which does indeed have a 4010 Princess-style net mounted behind the coin track.  To salvage some value from my wayward inquiry, here are some nice pics of a 4228 (no mounting tabs that I see) from beatriceco.com:

Various mounting brackets snap into the ends. 

There are also versions which did not have the gray top terminal ID plate.  For example in the ComKey 416 a small 5-pin socket with spade tipped leads was connected to the screw terminals, the top plate was omitted since all necessary connections were on the socket, and there were no brackets since it snapped into a molded cavity in the bottom housing.  This version also had no ringer capacitor.

The 1980 Commercial & Gov. Sales Catalog listed about 30 different variations with letter suffixes going into 2 letters.  The ComKey version was a 4228AB IIRC and wasn't the last on the list.  I don't know whether the 5-contact socket was formally part of the 4228AB network.