Hi.
I am reading a lot about switchboards...and learning a little.
My question for the day:
Are there any examples of RESISTORS in schematics for Kellogg crank switchboards?
or for any other type using crank phones to communicate.
I refer to the small ones "supposedly" located inside the board. I have not seen this yet.
and used to lower the voltage to the subscriber phones when used in common 24 volt batt installation.
also, used to lower voltage for the supervisor lites etc...
I believe this is accurate, but, well... still learnin a bunch about these things.
Regards.
Rod
A single resistor is used to limit current, not voltage.
But multiple resistors may be used to design a voltage divider, based on the concept that the resistor has a voltage drop across it, when current flows through it. But when no current flows, the voltage before and after a resistor is identical, there is no voltage drop across the resistor, according to Ohm's Law: E = I x R.
Old switchboard usually don't have many resistors, but the need does arise for limiting line current and for those purposes they often employ tungsten lamps, they were called resistance lamps.
I think it would help answering your question if you cite your source for "supposedly located...".
I suppose you mean a manual magneto switchboard with "crank switchboard" ? Typically, resistance lamps are only used in powered common battery switchboards, I believe.
Hi Unbeldi, Thanks for the reply.
A little background...
Always a tech. limited only by my tiny brain, always lookin through a glass ohm meter, if you will.
What can I do with that?
Well, I have 3 crank phones. and two grandchildren.
Why not a switchboard? Sooo...
I am building one so my grandchildren can experience a piece of history sadly gone from life.
And so they can talk to grandpa, and each other. "home day care".
I am building my switchboard based on a pic in the CAphonehandbook.pda, page 137
My situation, I don't have nore want simple...it just does not work for me, too many limits.
I need to be able to connect almost any type of phone together...crank type that is...
Thats why I am building a board.
The Type A model 6 switchboard allows both 2 and 3 wire connections. grounded, and metalic. as I understand it any way.
So I am basing my board on that one.
Now the hitch... I don't have resistor lites, and correct relays/drops, from the original systems.
I need a work around.
So, Reading what I can find about these old boards, I hear about resistors, and resistor lites.
I have not read that deep yet, head is still spinnin from all the variances in these things.
My board will use regular lites for the "line busy", and or ring off indicators.
I have the tip and ring lines wired.
I am now working on the sleeve circuit.
I understand touching the tip of a cord to the sleeve of a subscriber, would light a lite if the sub phone was off the hook...???, or on the hook?
That's my goal for this part.
I need the lites to lite when the call is terminated.
I thought from my reading, that resistors were used for part of this circuit. but cannot find any examples.
Maybe I just need to read some more? for simple circuits, these things get complicated.
Sorry about the book...any help is appreciated!
Ah, now I remember your earlier posts about building a switchboard. I didn't make the connection until now.
I think you have a lot of stuff to learn, don't be offended, please, but good preparation and a clear concept is needed to succeed with such a project.
I thought about you when I saw an eBay sale recently of about a dozen switchboard key panels that likely came out of a cordless switchboard, but the cost was rather high. IIRC, it was around $200, certainly more than I would pay for a small board. I got my cordless Kellogg board for only $50.
The first concept you have to understand is the difference between a local battery magneto switchboard and a common battery switchboard.
Local battery (LB) magneto boards don't have indicator lights, they don't have any power supplies to provide the current. Supervision is solely by using the generator to alert the operator, in which case a mechanical signal, such as a 'drop', is activated on the board, and the user is required to 'ring off' when done with the call, to alert the operator to disconnect the call. The operator alerts the user of an incoming call by also cranking the generator so that the subscribers bell rings.
Indicator lights are activated on common battery circuits when the subscriber goes off-hook, completing the circuit so that current flows to power the lamp.
For running just magneto ("crank") telephones you should build a local battery magneto board. There were two principle varieties of those. The switching can either be accomplished by plugging cords into the jacks connected to the telephone station lines (corded switchboard, or cord board), or by mechanical keys that use switch contacts to make the connections. These are called cordless switchboards and don't have any jacks or switchboard cords on the front panel. While easier and perhaps less error-prone to operate, cordless boards were more expensive and were built for only small installations for typically up to twenty stations. The most typical boards had perhaps seven to ten stations and two or three trunk lines for outgoing calls.
I would recommend reading one of the classic handbooks on manual switching, written by the contemporary experts of the field.
Here is just a small selection, some of which should not be hard to find online.
*Miller, Kempster (1905) 4th edition: American Telephone Practice
*Miller, Kempster (1933) Telephone Theory and Practice Volume 2; Manual Switching and Substation Equipment.
*McMean S.G., Miller K. (1912) Telephony
*Cyclopedia of Telephony and Telegraphy (1919) Vol 1 of 4
*Principles of Electricity applied to Telephone and Telegraph Work (various editions 1928 to 1961), AT&T Long Lines Department
As a sample, I attached the chapter of McMean & Miller about simple magneto switchboards as a PDF file. Perhaps this helps. With some search you will find many other texts that discuss the principles.
Coming back to resistors. All switchboards and telephone circuits require certain resistance levels for proper operation. In the early switchboards most of these requirements in the switchboard were achieved by proper design of the relays involved for switching and signaling. A resistor basically wastes energy, so it is better to let the current do useful work, such as dropping a signal flap, while being wasted.
Getting an old switchboard working again, in conjunction with some telephones, is fun and a rewarding experience. Building one from scratch is challenging, despite the apparently simple principles involved. I commend you on your ambitions!
I'm not sure I will recommend such project for only 3 phones, you may need one of them for the exchange service, and then...
An the other hand, the simplest working circuit I know is to this x-German exchange: http://tinyurl.com/lqv8e74 (more documentation linked)
I would probably go for ring signals e.g. 1, 2 or 3 rings, and all 3 phones on the same pair.
dsk
Thanks for the replies. I started out to build a simple crank board. but I don't have any drop parts, so no rattle.
I have to use lites. so, it got more complicated.
Thanks, Unbeldi, for the doc.
there is more info there, than I have found so far. so more reading.
I have a pretty good handle on crank/two wire connectivity.
However, finding the correct parts to make it work...well...
So, I decided a common batt board would be easier to work with...I say easier...
it is a bunch more complicated! but, I will get there.
can you tell me how, if the sub phone runs locally on about 3-5 volts, how did they kick that down on a common batt board?
or was the 24 volts common to all sub phones as well as the board?
If you are going for a common battery board, the LB telephones will not be suitable.
If you build a board like this (http://www.classicrotaryphones.com/forum/index.php?action=dlattach;topic=16132.0;attach=158848;image), using regular 2 pole on/off switches as TT and stereo plugs/jacks, you will almost there, a battery lamp (or led) circuit with an thyristor as relay, you could get it working. the thyristor holds the current after receiving a signal, until shorted, or power is removed. You have to make use of diodes, and resistors to tune in the sensitivity. It should not trig far to easy, let say it should have at least 25V to trig, and still dont break down at mains voltage.
To your last question, the voltage at the subscribers end is not important, but to feed the transmitter with a suitable amount of energy the current should be 18-50 milli amps, where 25 should be ideal. This will often cause a voltage at the phone of something like 5 Volts. The same current will be used in a relay to indicate off hook. Coils or relays in both lines offers high resistance (impedance) for the AC/sound part of the signals, so the signals will not be weakened to much. Suitable battery voltage for such circuits will usually be from 24-60V
dsk
Quote from: RB on March 23, 2017, 11:50:14 AM
Thanks for the replies. I started out to build a simple crank board. but I don't have any drop parts, so no rattle.
I have to use lites. so, it got more complicated.
Thanks, Unbeldi, for the doc.
there is more info there, than I have found so far. so more reading.
I have a pretty good handle on crank/two wire connectivity.
However, finding the correct parts to make it work...well...
So, I decided a common batt board would be easier to work with...I say easier...
it is a bunch more complicated! but, I will get there.
can you tell me how, if the sub phone runs locally on about 3-5 volts, how did they kick that down on a common batt board?
or was the 24 volts common to all sub phones as well as the board?
Local battery telephones are fundamentally different in design than common battery telephones. You do need to learn the difference first.
A local battery telephone does not work on common battery switchboard, and vice versa.
If you want to use your existing magneto telephones, you need an LB magneto switchboard.
The lack of historical parts is always difficult, but they do show up. But if you don't mind modern parts and technology, a traditional electromagnetic drop can be replaced and simulated with an LED circuit.
This forum post (http://www.classicrotaryphones.com/forum/index.php?topic=678.msg7914#msg7914) contains a book (Understanding Telephone Electronics by Bigelow) that you might find useful for the principles of the telephony.
Originally, and historically, LB telephones did not require or use a switchboard. The phones were installed in parallel on a pair of wires (originally one wire) and were used to intercommunicate among the members of the party line, generally farmers in a very rural environment. It was only after several lines were run in a radiating footprint from a central location (a town center of commerce, as an example) that the parties of one line, needing to communicate with the parties of the other lines, joined forces and installed a switchboard and hired an operator to act as the "central."
To build, from scratch, a switchboard, either LB or CB, is going to be a daunting task. You would be better served to allow the grandchildren to use and understand the phones as they were originally intended, that is, using coded ringing to call, and one long ring to "ring off" at the conclusion of a conversation.
The alternative is to find a military switchboard that was designed for magneto phones. They are available occasionally on Ebay and at telephone collector meets. Look for, as an example, the Signal Corps model SB-22.
http://www.prc68.com/I/SB22.shtml#Compatible (http://www.prc68.com/I/SB22.shtml#Compatible)
Quote from: Victor Laszlo on March 23, 2017, 07:15:39 PM
Originally, and historically, LB telephones did not require or use a switchboard. The phones were installed in parallel on a pair of wires (originally one wire) and were used to intercommunicate among the members of the party line, generally farmers in a very rural environment.
Yes, in a previous thread, we already went through that. It would be a good way to start some experience with the technology, of course, if a switchboard is actually needed.
Thanks guys for your insight.
very helpfull!
is is a long journey, but fun as can be at the same time.
You have to hurry up before your grandchildren grows up ;D This page has some ideas about thyristors, this may help replacing the indicator http://www.electronics-tutorials.ws/power/thyristor-circuit.html, and the extreme simplified circuit her does really work so you may use it. It is still magnet, and you will need one of your phones as operators set.
Please hook up the 3 phones on a common line until you have your exchange running, maybe they will get and keep interest for old technology. ;)
dsk
Hi All...
Still at this switchboard project. Thanks for all your help thus far, the project progresses.
This is the next part of it. A 20-A repeating coil, wired through a 4 pole 2 throw rotary switch.
As I understand it, this pic shows how to wire a Repeating coil for CB or LB application.
I will be installing this in the rear of the board.
Please take a look at it, and tell me if I am on the right track.
also, I see caps used for various reasons, too, anywhere from 1/2 mf to 2 mf.
Could you explain to me the reason you would use a 1/2, 1, or a 2mf cap in this application?
I assume, it has to do with the complete circuit, board and sub set ... but not sure.
Quote from: RB on April 07, 2017, 11:50:19 AM
Hi All...
Still at this switchboard project. Thanks for all your help thus far, the project progresses.
I would think it will take quite a bit longer yet... :o
No reason to apologize.
Quote
This is the next part of it. A 20-A repeating coil, wired through a 4 pole 2 throw rotary switch.
As I understand it, this pic shows how to wire a Repeating coil for CB or LB application.
I will be installing this in the rear of the board.
Please take a look at it, and tell me if I am on the right track.
also, I see caps used for various reasons, too, anywhere from 1/2 mf to 2 mf.
Could you explain to me the reason you would use a 1/2, 1, or a 2mf cap in this application?
I assume, it has to do with the complete circuit, board and sub set ... but not sure.
You are going about the project the wrong way; this way it will take many years to get a complete board working, perhaps never.
You cannot start with individual components. You need to start with a high-level design with features and functionality in mind.
You need to first define what your system can do, how you are going to operate it based on your needs or ideas.
It is ok to experiment with parts, but it seems you need to learn the basics of electronics first, the functions of resistors, capacitors, and inductors, and transformers, Ohm's law at least, and the basics of impedance, reactance, inductance.
We scanned and posted as a PDF file a Bell System training manual on the forum some time ago: Electricity for the Telephone Man (http://www.classicrotaryphones.com/forum/index.php?topic=4930.0)
It has the basics, and provides pictorial examples of concepts and measurement setups.
A little more advanced is this book, cheaply found on EBay: Principles of Electricity applied to Telephone and Telegraph Work (http://www.classicrotaryphones.com/forum/index.php?topic=8853.0)
Spending a few weeks or months learning and planning, will save you years in failed experiments.
Along with the books mentioned, which are certainly good reading to acquaint yourself with the basics, you might consider "jumping ahead" to BSP's for WE magneto boards, or TM's for military signal corps magneto equipment.
Looking at your diagram, I'm not clear what it is you're trying to recreate. And "recreate" should be your goal, not "create." In other words, "reinventing the wheel" which is always a time-waster. For starters, there is a very exact, and very proprietary, method of drawing telephone circuits. Most of the major manufacturers in the US use the same conventions. For starters, the Tip and Ring of any circuit need to be labeled. There are conventional symbols for capacitors, resistors, lamps, keys and coils. Contacts are generally shown in the "detached contact" method, with an X indicating a make contact, and a - indicating a break contact. Take a look at any BSP for a telephone or key telephone unit and you will get the picture. We can help better if we all speak the same language.
You mention sleeve leads, but there are no sleeve leads necessary in basic magneto service. Magneto service, using drops for indicators, was invented before the availability of reliable miniature lamps. Lamps use electricity from a supply. Supplies were not available and reliable when magneto service was introduced.
You asked about touching a cord tip to a station jack sleeve. That is a busy test used by operators at a CB cord board that is not equipped with station lamps, such as a 552 or 556 used in association with a dial PBX. A station sleeve is open when a station is idle. When a station is busy, its sleeve is grounded through a relay to battery. Since the cord tip is at ground, and there is a small potential difference between it and the grounded station sleeve, the operator will hear a click in her headset when she touches the tip of a cord (with its associated talk key operated) and the station jack sleeve. That indicates that the station is busy and she should not plug in, which would interrupt the call.
You mention "resistor lites". Do you mean, perhaps, "resistance lamps?" They are used in series with machine- or hand-ringing supplies to absorb generator at the moment that a called station goes off hook and before the supply can be released. There is one per switchboard. A standard Edison base lamp can be used as a substitute. Resistance lamps are generally available from collectors or on auction sites.
If you are puzzled by the capacitors you mentioned, that puzzlement indicates to us that you need to educate yourself in basic telephony. Look at a diagram for a typical LB phone, then look at two of them, wired together. Trace a call through them, both signalling and talking. Then take a big jump and look at a diagram for a LB switchboard and trace the progress of a call through all three items.
You are to be commended for your eagerness to learn telephony, but as you can see, I hope, there are, above, 300 words, written by just one guy, about a tiny sliver of the world and history of telephony. For you to learn, and then apply, everything that you need to know about just one little aspect of the whole realm of this art, would take a lifetime of experience.
Since you don't want to install them the way they would have been installed historically, the simplest way to do this is as follows:
Designate two magneto telephones as "subscribers" 1 & 2.
Install them at the ends of two pairs of wires.
Designate third telephone as "central."
Make or buy a wooden box with three telephone station jacks.
Wire 2 of the jacks across the line wires 1 & 2.
Install 2 line ringers at the box, across the lines of the two subscribers.
Install 2 ~60 Volt, A-C relays, each in series with a 2.0 mfd capacitor, in parallel with the above ringers.
Install 2, 6 Vdc relays that operate on the make contacts of the above relays.
Provide a 6 Vdc supply at the central box. (4 "D" cells)
Install 2, LED's at the box, adjacent to the jacks that they serve.
Wire the D-C relays to lock up on their own contacts.
Provide a N/C (break) push button in the lock-up supply path to release those relays.
Wire the lamps on a second set of contacts of the relays through the local supply.
Connect the third (central) magneto phone to the third jack.
Use a short double-ended cord to plug into the station jacks.
OPERATION
Either subscriber (1 or 2) rings in to central.
Ringer activates.
Ring up relay operates.
Lamp relay operates and holds.
Lamp comes on.
Central takes down receiver and plugs from jack 3 into calling jack 1 or jack 2 and asks for instructions.
Calling party asks for called party.
Central plugs into called jack and retires lamp by operating push button.
Central rings called party and announces call.
Central plugs cord from jack 1 to jack 2 and hangs up.
Parties converse and ring off.
Central pulls down connection.
---------------
This scheme approximates a situation where there are two party lines connected via a central magneto office. In this scenario, there is only one party on each party line.
Materials:
Box w/ three jacks.
2 relays.
2 ringers. WE type E1B or E1C are perfect. They have capacitors inside.
One double-ended two-conductor cord. Surplus or make your own.
The LED's and latching relays are added to substitute for mechanical drops. If you can find drops, you can eliminate the LED's and the 6 Volt supply.
Small Western Electric wooden telegraph service boxes with three jacks are often found at phone shows or on Ebay. If you want to know why there are lots of 3-jack boxes around, I can teach you how long-distance telegraph lines work in another thread.
No keys, coils, switches, or any other stuff required.
A corded switchboard as described would indeed be a better start to gain some experience, and if nicely assembled would work much like some old real board.
Shown below are the Western Electric cord boards from a 1907 catalog.
The first needs a separate operator telephone, and the second has it built in.
A simple cord board like Victor described can easily be expanded simply by adding more line circuits beyond the two initially installed. The design also permits as many simultaneous talking paths as desired, by using multiple jumper cords. Most cord boards and especially all cordless boards (with switches) had a fixed number of calls that could be conducted simultaneously, simply because each talking path requires some hardware and then the design involves a cost-versus-usage argument.
However, Victor's design has one drawback which I feel needs to be addressed. It does not provide any means for the operator (central) to listen in on an established connection to determine whether the parties are still in communication if they forgot to ring off at the end of the call. The operator would have to interrupt the connection to plug herself into one of the lines and ask the subscriber. Forgetting to ring off was a common problem with magneto switchboards, many people even forgot to hang up the receiver to take the phone off-line. To combat the latter problem on party-lines, each set was equipped with a "sure-ring" condenser, which provided a higher impedance to the set at ringing frequency to permit other ringers to still operate.
To permit the operator to listen in on a connection, you may simply provide two jacks for each line, wired in parallel. The second jack is then always available to patch the operator into the circuit. It can also be used to connect more than just two lines into a call, creating a conference call.
Quote from: unbeldi on April 08, 2017, 10:13:44 AM
...However, Victor's design has one drawback which I feel needs to be addressed. It does not provide any means for the operator (central) to listen in on an established connection to determine whether the parties are still in communication if they forgot to ring off at the end of the call. The operator would have to interrupt the connection to plug herself into one of the lines and ask the subscriber.....
To permit the operator to listen in on a connection, you may simply provide two jacks for each line, wired in parallel. The second jack is then always available to patch the operator into the circuit. It can also be used to connect more than just two lines into a call, creating a conference call.
Or, the extra jacks could be associated with each cord pair, rather than each line. Notice that in the top photo, there are 4 additional jacks, one per cord pair. The single cord (with some kind of designation above it -- TK? --) is plugged into the jack that is located above the 2 cords that are being use to connect lines 5 and 8. That single cord is probably associated with the operator's desk stand. Thus, only 4 additional jacks (one per cord pair) are needed rather than 10 (one per line). This is consistent with the design of later cord boards where the talk and ring keys are associated with each cord pair.
Quote from: poplar1 on April 08, 2017, 10:50:12 AM
Or, the extra jacks could be associated with each cord pair, rather than each line. Notice that in the top photo, there are 4 additional jacks, one per cord pair. The single cord (with some kind of designation above it -- TK? --) is plugged into the jack that is located above the 2 cords that are being use to connect lines 5 and 8. That single cord is probably associated with the operator's desk stand. Thus, only 4 additional jacks (one per cord pair) are needed rather than 10 (one per line). This is consistent with the design of later cord boards where the talk and ring keys are associated with each cord pair.
Certainly. That's what historical boards do. However, it makes the mechanical design more complex and introduces the limitation of a fixed number of talking paths.
It's the same trade-off that I mentioned earlier. 1/4" phono jacks are cheap and easy to add.
Another option is the addition of a simple two-pole push button for each line to connect TIP and SLEEVE of the line to the operator circuit.
Instead of using cords to make the connections between lines, some switchboards also used plugs that shorted two closely positioned jacks, arranged as part of an array of lines and talk circuits.
Pictured here is such a German switchboard by Siemens & Halske, a cordless switchboard. I haven't seen any of this kind made by American manufacturers, whose 'cordless switchboards' used keys instead of plugs.
I drew a circuit diagram of Victor's switchboard design.
I added two items:
- the previously discussed monitoring jack
- a resistor R1 to limit the current through the LED
R1 is needed to prevent the LED from burning out, and needs to be dimensioned according to the supply voltage, the forward voltage drop of the LED that is used (it depends greatly on the LED color), and its maximum current specification. So, if it is a 20 mA diode and has a forward voltage of 1.8 V, and the supply voltage is 5V, then the resistor should be (5 – 1.8 ) / 0.02 in ohms, but I would use something larger as long as the LED still glows. 220 Ω should be good enough for any 20 mA LED.
You can also use a lamp instead of the LED, but in that case I would wire the lamp directly into the relay coil circuit. Doing so with an LED requires a relay that operates on only 20 mA current. Those probably get a little more expensive, and antique relays from old switchboards require more current than can be pushed through modern LEDs.
If I wanted to build this, I would also try to avoid using two relays, and instead use a semiconductor, or optocoupler, to detect ringing on the line.
I indicated a supply voltage of 5V in the diagram. This is not important, but it is easy and cheap to find an old cell phone charger, that almost everyone these days has in a drawer of old stuff these days. It would make a good and cheap power supply.
The diagram shows only one station line circuit. Of course you want to duplicate that for as many lines as your switchboard requires. When building for more than two lines, you might also move the reset push button switch into each LED relay circuit, so that individual lines can be reset, in case more than one call alert comes in at the same time.
For only two lines it is not a big problem to use one ringer per line, but for more lines, the space problem multiplies rapidly, as can be seen in one of those historic switchboards that I showed earlier. I would devise a method to use only one ringer that is triggered by a relay from any of the lines. Of course, the ringers could be omitted altogether, if no audible alarm is needed and you are sitting in front of the board all day to play operator for your kids. ;D It might also be possible to replace that AC relay (RY1) with a DC relay and use it as a buzzer, as it will flutter about 16 times per second driven by the ringing voltage from the magneto generator of the calling station. If the relay itself does not make enough noise, a second set of switch contacts could drive a DC buzzer or ringer.
@RB: Are you still with us?
Great schematic! It's as though you read my mind! (or my post)
I would have included some way to monitor the line, if the application had been more...commercial... in nature, but since the system proposed has two subscribers it didn't seem to be immediately necessary.
There are other refinements to a real working magneto system, to be discussed if and when the OP returns to the thread.
Hi Guys
Yup, still here, in spirit, anyway.
been busy doin grand babies, and life in general...
I am currently working on the repeat coil circuit.
it has to be switchable from LB, to CB...so takin me a bit to get the switches wired.
big fingers, small work space.
Thanks for all the wisdom!!!
will study the new diagrams, and post back, thanks again.
Quote from: RB on April 18, 2017, 03:57:30 PM
Hi Guys
Yup, still here, in spirit, anyway.
been busy doin grand babies, and life in general...
I am currently working on the repeat coil circuit.
it has to be switchable from LB, to CB...so takin me a bit to get the switches wired.
big fingers, small work space.
Thanks for all the wisdom!!!
will study the new diagrams, and post back, thanks again.
Switchable from LB to CB ?
Hmm. Never heard of that.
Common battery PBX switchboards often had the option of installing a tie trunk unit to permit connection to an alternate magneto exchange or local magneto board. Those tie trunk are dry and basically the same as a local battery line.
Is that what you mean ?
Here is an interesting and quite stylish looking cordless magneto board of ca. 1908 by the Century Telephone Construction Company. This is almost the same time as the first cordless boards by the Western Electric Company, the 505 for CB and the 10-Line Magneto Switchboard for LB, both of which where clunky rectangular wood boxes.
Found in Telephone magazine.
Another board of the time was this 10-line magneto board by Stromberg-Carlson.
Good morning.
not sure what a tie trunk unit is...still learnin.
I do believe, however, that we are saying basically the same thing.
I have collected schematics for both LB and CB repeat coil configurations.
From those, I have combined "via 2 rotary switches", a solution which allows me to convert on the fly, from LB to CB.
I had to use 2 switches because I could not get my hands on the correct 1 switch solution. So, there we are.
Still in the wiring up stage, There are a lot of wires associated with this part, and my eyes are not gettin any better.
Should have it completed by end of weekend.
I intend to use this board as a teaching tool. As well as a fully functional switchboard. That is why I go to these extents.
The board will be able to support any basic 2 wire crank phone connections, "straight through the board".
And, if needed, the ability to insert the repeat coil, to isolate the two lines from each other.
Overkill you say??? sure it is, but who is judging? I can do this any way I choose. AND, it is fun as heck!!!
Well, not all fun, I hate that I need to work under a BIG-EYE mag lite to see well enuf to solder.
I WILL, however, emerge victorious!
Next week, if this weekend goes well, I will get back to the signaling circuit. ??? is that the right term?
Thanks to all of you for your interest/input. It is helping speed this up a bunch!
A tie trunk, is just a telephone line connecting two switch boards. For magneto service, it has no battery on it, and is essentially the same as a local battery telephone line.
A repeating coil is typically used for transmission between two dissimilar type of lines to avoid inductive noise problems. An example is when one line is a ground-ringing line and the second rings across tip and ring only without the need for ground.
When building a switchboard, you will probably only have one type of line, so a repeating coil would not be needed. When transmitting from a local battery line to a common battery line, you don't necessarily need a repeating coil, you can often simply use a capacitive bridge circuit. Some switchboards with repeating coil circuits even had a feature key that eliminated the coil, called a zero-loss key, because the use of repeating coils does introduce transmission losses.
A signaling circuit is the part of a telecommunication equipment that receives or sends the information for call control. So, that includes ringing, on- and off-hook detection (supervision), and address transmission (dialing).
I am a bit concerned about your project, to be honest. I know how much fun it is, indeed, but it would be more fun to build something simpler that in the end works. Eventually, you might be able to find a cordless board for little money, they do exist and collectors do retire from their hobby as well—everyone MUST eventually.
Good morning. Thanks for the reply.
I want to ease your concern a little.
I have been doing this sort of design/building for some time now.
my board is and will continue to function just as I have designed it to... ok, not my design, per say. but I modified it.
I was gonna wait till I had it a bit more assembled, but I think a pic or two, is warranted at this point.
I built the subscriber jack this weekend, and will repeat it 3 more times for a 4 subscriber board..so far, anyway.
After the jack assembly, it will be on to the signaling part, and then to the finish line...
Thanks again, for all the support.
Thank you for the pictures. It looks like you do have a vision and a plan.
That's all I can tell right now. A full circuit schematic would make it much easier to comment.
Best of success.
Thank you!
I will provide schematics and more pics when completed.
This is a fun project.
What shud I call it??? Frankinphone? lol
The LB side is complete! and working...
The CB side is almost complete, still working on the line lites, but everything else is there.
I posted the board in another post, "My new, vintage switchboard" but no response yet.
chk it out!