Making a WE551A Functional - Work In Progress

[TelePlay]

Can anyone who has a 551 with a fuse panel take a picture of the fuse panel so ramegoom knows what he needs in there was one in there in the first place, and not somewhere else?

[Alex G. Bell]

OK, back to being baffled. I can't find fuses anywhere. The illustration on the data downloaded showed what appeared to be a fuse panel in back, adjacent to the relay panel. Nothing there but the weighted cords.

Any idea where I might look to find a fuse panel? I've been through it and nothing even remotely looks like it'd be a fuse.

I'm not certain whether there should be or not.  Some of the SDs I reviewed related to the battery supply cutoff key show fuses.  Where they are located is unclear.

I described what they look like in a previous message.  If there were any there's a high likelihood that they would be mounted on a white glazed ceramic block, but not necessarily.

[tanderson78]

Any chance I can get a key like the one you made?  I've had a nice 552 since April that I want to tinker with and it didn't come one.

Can anyone direct me to a post or thread that identifies some of these models and when they were made?

[ramegoom]

Here's what I did. Had a guy who posted a video on his 551A send me a pic of his key. Then I attempted to replicate it based on the picture, using a piece of aluminum. Got it to actually open. Once I got it opened, I took it apart. Two latch plates on each side. So I came up with a sort of measurement that would work.

Next I ordered a blank on Ebay. This one will work:

http://www.ebay.com/itm/Vtg-Antique-old-Hollow-Barrel-Double-Bit-Uncut-Cabinet-Lock-Padlock-Key-Blank-/263066841801

?hash=item3d400172c9:g:wy0AAOSwOMdZWD9y

Or this one:

http://www.ebay.com/itm/Real-Vtg-Antique-old-Hollow-Barrel-Split-Double-Bit-Uncut-Cabinet-Lock-Key-Blank-/263066837832

?hash=item3d40016348:g:v0IAAOSw0j9ZWD5g

Then I got out the dremel tool and a bench grinder and made one that fit perfectly. Took a bit of patience, but it paid off.

Here's the temporary key vs. permanent key that I made:

[unbeldi]

OK, back to being baffled. I can't find fuses anywhere. The illustration on the data downloaded showed what appeared to be a fuse panel in back, adjacent to the relay panel. Nothing there but the weighted cords.

Any idea where I might look to find a fuse panel? I've been through it and nothing even remotely looks like it'd be a fuse.

Look at the BSP 536-490-210, entitled "Installation", in the BSP pack that I posted.  On page 6 it shows the connections for the central office battery feeds with protectors. PBX systems most often were powered not from a local battery or power supply, but from one or two feed pairs from the central office.  The protectors (#62D with 24-C 2 Amp fuses) are said to be mounted on the rear of the front panel on the 551A and on the rear of the cord shelf on the 551B.

On the 551A the battery cut-off key should be pretty close to the protectors, it might be easy to back trace from the key to find the proper connection point.

However, from your picture of the inside toward the rear of the front panel, I don't see the protectors.

[ramegoom]

NOWWWWW it's starting to make sense. I looked at that battery setup, thought it was some sort of backup. But NO. It's the SUPPLY for this system.

Looking at the wiring diagram on the wood board, it shows it pretty clearly. I'm going to step off the deep end and assume my markup is correct.

I now need to find a pair of phones to hook up to this system, then I'll attach my 24V power supply.

[Alex G. Bell]

Look at the BSP 536-490-210, entitled "Installation", in the BSP pack that I posted.  On page 6 it shows the connections for the central office battery feeds with protectors. PBX systems most often were powered not from a local battery or power supply, but from one or two feed pairs from the central office.  The protectors (#62D with 24-C 2 Amp fuses) are said to be mounted on the rear of the front panel on the 551A and on the rear of the cord shelf on the 551B.

On the 551A the battery cut-off key should be pretty close to the protectors, it might be easy to back trace from the key to find the proper connection point.

However, from your picture of the inside toward the rear of the front panel, I don't see the protectors.

Well, not exactly.  Para. 3.31 ans 3.32 say: "when specified" and para. 3.33 says that no fuses are required for a single position board.  So perhaps there aren't any and perhaps that's why we didn't see them.

[Alex G. Bell]

NOWWWWW it's starting to make sense. I looked at that battery setup, thought it was some sort of backup. But NO. It's the SUPPLY for this system.

Looking at the wiring diagram on the wood board, it shows it pretty clearly. I'm going to step off the deep end and assume my markup is correct.

I now need to find a pair of phones to hook up to this system, then I'll attach my 24V power supply.

BAT is always negative in telephone equipment except for a few cases for example where vacuum tubes or coin collection in payphones are involved. 

If you compare the strapping shown in this diagram with the strapping found on terminals of the MISC terminal block, they will match and the leads connected to those strapped terminals are the BAT, GRD and ringing supply inputs from the 50 pair cable.

On your photo, it appears that the SL-YL, BL-VI, OR-VI, GN-VI and BR-VI pairs of the OR-WH binder are the DC input with BL, OR, GN, BR and SL the -24V pole and the YL of SL-YL and (4) VI mates the +24V pole, which should be tied to earth ground too eventually.

The VI lead on MISC-35 is an additional ground to the DIAL ckt shown on the version of the wiring diagram found in the TCI library.  I have not figured out yet what the SL lead on 26 is.

It might be worthwhile for you to take a photo of the complete T-623425 wiring diagram being careful to avoid reflections so it is completely legible.  It's clear that it's a better version than the one in the TCI library, a circuit label version whose number is cut off in the scan so it cannot be identified specifically, but it's very different and may not apply fully to your switchboard anyway.

[ramegoom]

So, the phone system uses a positive ground?

GRD and BAT

Where BAT is negative 24V and GRD is positive 24V?

Then, earth ground is equivalent to the battery positive supply?

[Alex G. Bell]

So, the phone system uses a positive ground?

GRD and BAT

Where BAT is negative 24V and GRD is positive 24V?

Then, earth ground is equivalent to the battery positive supply?

Yes, the entire phone system, world wide, uses + grounded battery supply.  I'm sure I read decades ago that this was for electrolysis prevention but some years ago when a bunch of us attempted to find that in print we did not succeed.

Yes, in this case BAT is probably -24V, though central office systems and larger PBXs use -48V.  My recollection is that some 551s may have operated at 18-20V. 

Fortunately this equipment is too old to contain electrolytic capacitors which would be damaged by polarity reversal and in the few instances where they were used for power supply filtering they had the foresight to use non-polar ones, anticipating possible accidental reversals.

Nice job on the keyshelf key.

Now that you have it open you should pull one of the red or white lamp caps off the keyshelf using two small screwdrivers in the gaps on each side of the cap, then see if you can push a lamp out from the back with a wooden match stick or pull one out by slipping a short length of vinyl insulating tubing of the right size onto the glass so we can find out their code # and look up the voltage.  That will be the best indication of what power supply voltage was used and is needed.  The lamps pull straight out without twisting.

The adhesive which holds the metal lamp base contacts onto the glass on many of these old lamps is very weak so extreme care is required to prevent the glass from coming loose from the contacts.  Even with the utmost care it may still come apart.  If the contacts come loose and the wire leads do not break off at the glass the contacts can be glued back.  RTV Silicone Rubber (Room Temperature Vulcanizing) is probably the best modern substance to re-secure the parts once the glass is cleaned of the old adhesive.

You may want to acquire proper lamp cap and lamp removal tools.  They're readily available.

[RB]

I have been drooling over that clean board since the first post...
A friend of mine worked as a lineman for the phone co in west Texas...poor bugger...for a long time. In ditches...
Spent much of his time chasing snakes and scorpions.
He confirmed what Alex stated.
Originally, they used neg ground, but found that the moisture in the ground, combined with the wires and connections, allowed for electrolysis.
So, reversing the plus and minus, warded off the process. it did not remove it completely, but significantly reduced it.

[ramegoom]

B2 light bulbs in the sockets. Used a piece of adhesive-lined 1/4 in. heatshrink to remove them. It appears the base insulation is made out of wood?

What voltage does it take to light these?

[Alex G. Bell]

B2 light bulbs in the sockets. Used a piece of adhesive-lined 1/4 in. heatshrink to remove them. It appears the base insulation is made out of wood?

What voltage does it take to light these?

Good work!

Yes, wood.  Lots of electrical and telephone parts were made of wood or hard rubber before Bakelite and thermoplastics.

B2 is 18V, 36-48mA. 

The life of tungsten filament lamps is very severely shortened by even small over-voltages such as 10%.  It's a high order inverse exponential relationship.  Most likely the switchboard operated from an 18-20V wet cell battery supply charged from the CO over cable pairs or from a 101G power plant which has a 20VDC filtered TALK output. 

To leave no stone unturned, I reviewed the cord circuit schematic SD-66179-01.  There is no resistance in series with the lamps which would drop the voltage applied to the lamps from the power supply voltage applied to the switchboard.  They operate directly from battery and ground, controlled by a relay contact.

24V will be very adverse to the lamps.  If you cannot find an 18V supply or modify the regulation of one, you can drop the voltage from a 24V fixed supply by connecting a string of 2A diodes in series with the output, figuring ~1V/diode.

Most likely the station line lamps are K2s, which are always used there over a wide voltage range and are rated 30V.  But that's why the very transparent amber lamp caps are required on the station lamps.

[Alex G. Bell]

A friend of mine worked as a lineman for the phone co in west Texas...poor bugger...for a long time.
He confirmed what Alex stated.
Originally, they used neg ground, but found that the moisture in the ground, combined with the wires and connections, allowed for electrolysis.
So, reversing the plus and minus, warded off the process. it did not remove it completely, but significantly reduced it.

Thanks!  At the time a bunch of us tried, I thought for sure we would find it in writing in the AE Training practices I "cut my teeth on" or in "AT&T Principles of Electricity & Magnetism..." but we did not find it.

[unbeldi]

Yes, the entire phone system, world wide, uses + grounded battery supply.  I'm sure I read decades ago that this was for electrolysis prevention but some years ago when a bunch of us attempted to find that in print we did not succeed.

The process is called cathodic protection. It is not at all unique to telephony.  It was known in the early 1800s, and I think it was even used to protect copper ships at one time by making the hull the cathode of an electrochemical cell. It was and probably still is used to protect pipelines and all kinds of metal structures. The principle can also be used to reverse rusting on tools by connecting them to the negative pole of a battery and immersing the tool into a suitable electrolyte cell connected to the positive pole of the battery with a suitable anode.

Oxidation is the removal of electrons from a metal to turn its atoms into positive ions.  When the metal has an excess negative charge with respect to ground, then the removal of electrons is much harder, and thus the metal is somewhat protected from corrosion.

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