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WE 555 PBX - just flew one in last weekend, hoping to get working

Started by rglenn, July 04, 2020, 08:06:17 AM

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Is the Western Electric 20B2 Power Unit an appropriate power supply for the WE 555 PBX?


Well, that looks like a 24v power supply.
So, if your board has 24v bulbs, that part should work. but that's not all...
I don't know all the variations of power supplys,
The Sig output seems to be 24v??? maybe should be 90v??
I found this...
555 power supply info short version
The Tellabs 8050.  It's a switched mode unit, standby power is low if you choose to leave it powered up.  Switches between 24 or 48VDC and the ringing source to 20 or 30 Hz.  Switchboards always use 20Hz.  And a 10VAC 60Hz output for key telephone systems.

The 101G use saturated core devices to produce the ringing current which have much higher standby power consumption, heat production and are much larger.  The 101G versions which provide ringing provide 20Hz
-24VDC connects to CENT OFF BAT.
The + side of the 24VDC source connects to CENT OFF GRD.
The high side of the 90VAC 20Hz ringing source connects to GEN +/-.
The return side of the 90VAC 20Hz ringing source connects to GEN G.

I'm not sure whether there is an internal connection within the swbd between the DC GRD and the ringing GRD.  It would be good to check for continuity before making these terminals before making connections. 


I can't seem to find a Tellabs 8050 or 101g for less than $150.  Anything else that's less expensive and available that would work?

Jim Stettler

Basically, you need a filtered 24 or 48 volt DC power supply.
The key is filtered to simulate talk battery.
Talk battery was battery, a power supply can cause hum, That is why you need filtered to simulate talk battery.

If you have a 48V board, running it on 24 is fine and your lamps will last much longer.
I think you can find a cheap key system power supply that will satisfy your needs.
You could probably use a printer power supply, these are popular among the telephone switchers .
You could use actual battery.  AGM 12 volt batteries (alarm system batteries)  is another method of providing talk battery. Even if your charger isn't well filtered, you could  charge up the batteries when the system is idle.
Just some work around thoughts,
You live, You learn,
You die, you forget it all.


The 12 0r 24v DC power supply is easy...
most anything will get you goin. "per Jim's recommendations".
The 90v 20 hz ringer power is the killer.
That's why you need a good supply.
Nuthin runs on 20 hz today.
So, supply is limited.

Jim Stettler

There are old wall warts that provide 48VDC filtered (Wescom comes to mind)  for telephone systems, you can find the 24 volt DC as well.
There are also telephone system wall warts and small power supplies that can provide ring power.

You can also get ring signal from powerdesign type  ringer modules.
You would need to home brew a circuit to interject the ring signal, I think this could be a very simple circuit. Basically a relay based circuit interjecting a ring frequency.

The power-design type modules can also do frequency ringing, most are designed for 1 specific  frequency.

Black magic is one brand and I think they are sometimes on the forum
I could control the world given enough relays and proper interface components, that is the design power of relays.
You live, You learn,
You die, you forget it all.


A 20B2 will work fine.... except for the 48 volt side, that will have to be on a seperate PSU.


Could I use this?  Will the ringing @ 110V and 30Hz be a problem?


Quote from: Babybearjs on July 04, 2020, 07:17:14 PM
A 20B2 will work fine.... except for the 48 volt side, that will have to be on a seperate PSU.

I don't understand this statement. The 555 PBX will work on a variety of DC voltages, including 24 VDC *or* 48 VDC. You don't need both on the same PBX. (As others have stated, you do need lamps rated for 48 VDC if your power supply is 48 V output.)
110 VAC @ 30 Hertz is OK for ringing.
"C'est pas une restauration, c'est une rénovation."--François Martin.


The ring voltage is maybe a little high?
Don't know if that will be an issue.
The 30hz will make the station phone ring funny, won't sound as clean. but it would work.
Just read pops post, guess it would be ok.


OK, I found a power supply mentioned a few times in the forum for use on a 555 PBX.  As I have no idea what I am doing, I was hoping to get confirmation or corrections to the way I think it is to be wired before I blow everything sky high.

On the MISC terminal strip
Power supply 24v Talk - (A) goes to terms (1-4) should be strapped together
Power supply 24v Talk - (G) goes to term (45-48) should be strapped together

Power supply 110v ring (+/-) goes to term 21 (21-22) should be strapped together
Power supply 110v ring (G) goes to term 24

Where would the power supply GRD be connected?


If it is indeed a ground, "not the neg side of power", then it should be tied to the frame. imho
may not be needed.
Are there going to be any outside extensions connected?


Harry Smith
ATCA 4434

"There is no try,
there is only
do or do not"


Those power units are positive ground, not negitive.
So you have to remember that when using those.
And yes when your connecting to a key system or a box you must make sure your connections are correct before powering up.


Thanks everyone.  I do plan to have 2 extensions and a trunk assuming I can get anything to work.