Telephone Switching > Magneto & Manual (Cord Boards etc)

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

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

RB:
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. 

rglenn:
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,
Jim.

RB:
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.

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