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and very rarely ever needs repairs, once you fix them." - Dan/Panther

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My New, Vintage switchboard

Started by RB, May 08, 2017, 09:48:47 AM

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Ok, here she is...
the Magneto side is complete, and tested working.
The CB side is complete, but as of yet, untested.
I don't have any cb phones to test with...yet.
I will add some trim to clean it up a bit, but until I get two more
dpdt locking switches, i can't connect the second cord set.
I have a couple vids of the board, one is 109 meg, and the other is about 240m
do vids work ok on this sight?
Here are some pics, and yes, full schematics too! well, minus the drop board part.


pics did not work???
I must be doin something wrong???


ok, last pic.
I think she looks pretty good!


Awesome project! Looks like just the thing for a collector of LB phones.
My name is Kenn, and I like telephones.

"Progress isn't made by early risers. It's made by lazy men trying to find easier ways to do something." --Robert Heinlein


Thanks for the status report.
I was hoping for some diagrams that explain the concepts of your switchboard.
Of those shown, only the cord circuit resembles something I can relate to.   What exactly is a Type A Model 6 switchboard ?  Who made it ? Perhaps you can show the original circuit that was the basis, as stated.


Sure. I got the basic schematic from the
I did not need the extra stuff, just the key config.
It allows 2 separate connections, with the same config for both up and down. So, I made one side LB, "straight through".
and the other,connects  through a repeat coil,  and is  select-able for  LB or CB connections, and, since depending on the C.O.D. type used, the caps can be anywhere from .5 to 2mf, but 2 is best for cord circuits, I decided  to make it adjustable for 1 or 2mf across the coil.
the other selection is for the op set only. It gives me the ability to change components on the fly if needed.
I will be replacing the hand set with a head set when I find a suitable one, and I am sure, something will need to be modified.
So, that's the reason, here is the only place you will see a board like this one.


Ah, thanks.  I actually have that book too.

Looking at that diagram you posted, it is labeled "for connecting both grounded and metallic circuit lines".
This is the reason that the circuit uses a repeating coil.  In the prior discussions of your project I think I mentioned that a repeating coil is not generally necessary if the types of circuits that it is intended to connect are of the same type.   That is also expressed by this diagram.  Grounded lines and metallic lines must be interconnected with a repeating coil.  In your project you'll probably never have grounded lines, and that was the case in most small business PBX installation, and thus the talking circuits could be much simplified and reduced to simple interconnection, either direct or through coupling capacitors.

The coupling capacitors can simply be a 2 µF size, or larger, there should be no need to switch to others.

The book also provides a circuit for just metallic lines (or only grounded lines) in the preceding page, which would have been sufficient, and is much closer to the circuit idea suggested by Victor in the first discussion.

The conditions for which the board in the manual is intended are much different, and rather 'rough' in a forestry environment.   As you probably noticed the book describes installing transmission lines on trees through forests and mountains, and what ever else.   The book spends more time on building lines than on the switchboard.   The types of switchboards it describes, are actually built by the department itself, rather than from established switchboard manufacturers. The types of telephones supported is diverse from several of the well-known makers, such as Kellogg, WECO, etc.


Boy, have I noticed differences in the design of the different mfgrs. The ones I liked the best, I cannot find switches for. These are hard enuf to find!
So I landed on that schematic, and modified it as needed.
I also don't think I will ever encounter a grounded line, but different types of phones...almost certainly.
Guess I could have built it simpler, but this has been an educational journey, "I like those" , as well as just plain fun lol!
That book was indeed interesting reading. I am surprised they did not include a section on Squirrel control lol!
It seemed to be pretty much all inclusive, so I went with that.
So, I guess I would say, I have a Basic board design, with a few extra options  :)
You and Victor are amazing!
I would like to spend a day looking over your shoulders, just to see how you two work!
Thanks again for sharing your wisdom!


Now that we know the origin of the design, the designation also makes sense to me:  Type A Model 6.   The government entities seemed to like designating some equipment with letter types, Type A, Type B, Type C, etc.   For example, some Navy ship telephones are A, B, C, D, E, F.


Quote from: RB on May 09, 2017, 05:05:01 PM
I would like to spend a day looking over your shoulders, just to see how you two work!
Thanks again for sharing your wisdom!

I don't think I'll attempt building a mechanical switchboard though. Kudos to you.

Mostly because I have one, and I don't particularly value the lessons learned in that process, and I am not particularly interested in woodworking. It is also hard to source the correct parts, as you are finding out.

My interest is mainly in building electronic, digital switches, for which I can create myself any part I can conceive.
Here is a screenshot of my all digital VBX (virtual branch exchange), modeled onreplicating a 1930s' 1007-CC Kellogg Cordless PBX Switchboard, partly running in a web browser.  The keys, lamps, and audible signals operate just like the original.


Ok, Wow! thats a little deep for me. :o
nice lookin board!
I got out of digital, pretty much back in the late 80's.
Spent 8 years with TRW repairing Hazeltine terminal boards. They were still launching the shuttles with them...ooh!
Then that thing they call a PC came along...
Then on to pinball machines for a while.
Now, I stay pretty much with EM machines, no surges, no blown chips...much easier to work on.
I do miss digital though, somewhat.


The principles of this Kellogg PBX are very simple, simpler in fact than what you built.   It has connecting circuits for five simultaneous calls. Each of the twelve station lines and three trunk lines can be interconnected with another station or trunk on one of these connecting circuits with the front panel keys.  Two stations are directly connected by their tip and ring conductors without any additional components, no capacitors and no repeating coils.  Talk battery is connected to the ring conductor of the connecting circuit via a station indicator lamp or, on the larger 20-line board, via the operating coil of line relays that in turn control the supervisory line lamp.

The lamps (top row) light up whenever a station is taken off-hook; the hookswitch completes the circuit through the telephone and causes current to flow to light the lamp until it is serviced by connection to a connecting path.

The entire complexity of the switchboard comes really only from the lamp and audible supervisory signals.  The board has trunk and station lamps (white), connecting path supervisory lamps (red), and trunk supervisory lamps (green).  A lamp signal is turned on only when some action is required of the switchboard operator.  If the operator is not at the board constantly, i.e. not looking at the lamps all of the time, so that a secretary with other duties can function as attendant, the board is equipped with a buzzer that sounds whenever a lamp lights up.

The attendant telephone  can be a standard common battery telephone, or a headset telephone or other simple type, as the board also has a built-in induction coil for such an instrument.


Nice features. I like it a lot.


OK, a couple new pics. :D
I got the second cord set installed and working. looks pretty good.
I added a corrected pic of the OP set...this one works...
and a pic of the drop/extension circuit.
That's about all I am gonna do to it, other than some cosmetic details.
It will be fun for the grand kids to play with a working switchboard.
I put some temp tags with labels, I would like to find a few of the card plates/holders for some nice labels to finish it out.
Will be on the look out for those.