Building a network with a Pana AND 555 PBX...some Questions

[cadman]

After poking around the forums it sounds like a Panasonic 308 or 616 is just the ticket for my setup. I've got several buildings I'd like to run lines to, and be able to call building X from Y. We're too far from the road for a POTS, and when internet gets to us this year, I'm planning on going VOIP and understand the Pana PBX solves the pulse to DTMF problem. (Imagine, a phone collector without a phone line!) On the other hand, I have a 555 cordboard I'd like to set up to host a collection of phones in my museum/workshop, and this creates a real head-scratcher. Before I get too ponderous, can anyone shed some light on the Panasonic system....

1. Does the Pana system generate a dial tone for internal calls?
2. If I plug one of the Pana extension jacks into one of its own trunk jacks, and that extension is called, will all the other extensions ring as though the call is originating from a CO? I'm thinking this would be handy if the significant-other was trying to track me down on the property.
3. Does anyone know what happens if ringing voltage is applied TO an extension jack on the Pana?*

Now for the more ponderous... I'm trying to find an elegant way to incorporate both the Pana and my cordboard into one useful system. Anyone tried this before? I'm thinking the cleanest way would be to run one of the Pana's extensions into a vacant cordboard Trunk circuit.

Thinking out loud, if I picked up a Pana extension, dialed the extension for the 555 cordboard, the 555 trunk would "ring", the operator could plug in and direct the call to one of the 555 extensions. Conversely, if I picked up a 555 extension and requested a phone on the Pana exchange, the operator could plug into the Pana trunk, dial the local pana extension number, and complete the call. If there's a reason this wouldn't work, I'm all ears.

*I don't know exactly how the 555 trunk circuit works, but is there a chance that ring voltage could accidentally be applied to the trunk line leading to the Pana extension it's connected to? I don't know if the ring button is disabled for the cord used in that situation or not. Also, were there ringdown trunks on 555's?

[Phonesrfun]

The panasonic does generate its own dial tone, somewhat unique to itself, but also very much like a standard telco precise dial tone.

The panasonic should work well with a 555, except for the part about ringing back up to an extension port on the Panasonic.  I have not tried back-ringing, and I would suspect it might be problematic.  The Panasonic is 1980's solid state, and may or may not be forgiving if faced with ringing current.  Somewhere I have a schematic of the thing, and I could pass that along for you to study.  I, for one, am not one to determine whether it would be ok or not.

I have plugged an extension jack into a trunk jack and one can have all kinds of fun with that.  I have also put a trunk jack to the input of my SXS switch, so that I could dial "out" from the Panasonic and go into the SXS.

The Panasonic is a great piece of gear for not much $$.

[ESalter]

Hi Cory-

First off, you wouldn't be the first collector without a phone line.  At our museum pretty much any phone can call any other phone, but there isn't a single line going out of the building.

I don't know a thing about the Panasonic PBX's so I can't help you there.  I can offer a little bit about the 555 though.  Our operating setup right now includes a 3 trunk 555 cordboard, a WE 755A crossbar PBX, an AE 1 ckt demo SxS switch, and an AE 200 line 20 ckt SxS switch.  The big SxS switch isn't entirely finished yet, so it isn't directly connected to anything other than a trunk on the 555 right now.  That is, an extension from the big SxS is hooked to the first trunk on the 555.  The small SxS switch has one extension hooked to the second trunk of the 555.  It also has a trunk hooked to an extension of the crossbar switch.  So, I can pick up an extension phone on the small strowger and dial 6541(or whatever the extension is) and ring a trunk on the cordboard or dial 8 and be connected to the crossbar and dial one of its extensions.  Now, all that being said, lets say I am on an extension on the cordboard and want to call an extension of the crossbar.  The operator has to plug be into the second trunk(which accesses the small SxS), then dial 8(which accesses the Xbar) then dial the extension I want.  Doesn't apply to anything you're doing, but we have a 557 answering board also we're eventually going to hook up to the big SxS switch to handle incoming trunk calls.

I can also tell you the 555 doesn't disable ringing on any cords.  If you push the button, it rings.  Doesn't matter if it's connected to an extension, a trunk, or your fingers.

Does that help you at all?

---Eric

[cadman]

Thanks for the suggestions. Guess my next step is to pick one of these units up. I've read Version 3 is the one to get; any easy way to check that before buying?

Bill, I'll take you up on the offer for the schematic, I think that should tell me what I need to know. And Eric, thanks for the advice on the 555 ringing situation...I didn't know that! You guys with your SxS's make me envious    -Cory

[ESalter]

Hi Cory-

The Strowgers are neat and the big one is BIG, but my favorite is the crossbar.  It's just astounding to me to watch that thing operate.  As soon as I can I'm going to take a video of it and post it on here.

---Eric

[Phonesrfun]

Bill, I’ll take you up on the offer for the schematic, I think that should tell me what I need to know.   -Cory

I sent it to you via your e-mail in your profile.

[cadman]

Thanks Bill.

As to the question of whether the Pana might be damaged if ringing current were injected into an extension jack, I have to assume Panasonic considered this from the start. It'd be very easy to get a CO line accidentally plugged into an extension jack, especially if it happened somewhere remote of the unit.

For those interested, Fig 17 on Pg 17 of the Pana Tech Guide shows a pretty good diagram of how the Extension Circuit works.

When the PBX goes to ring a station, a DP relay switches the station wires directly over to ringing current and in doing so, takes the voice and logistical side of the circuit out of the equation. There's a pair of MOVs on the station wires which I imagine keeps ring current in check. Otherwise, that's it during signaling.

Now, when not signaling, I see a pair of diodes on each station wire clamped to ground (D302A and D303A). These are listed 1SS131. Looking at the datasheet I'm surprised to see they're high speed switching diodes with a pk reverse voltage of 90v. Hmmm. We've also got D304A and D305A which I cannot find on the parts list, but these appear to set one side of the ckt at grd and the other at -26v. And I see a pair of caps to grd which probably act more as a short to grd if a ring signal somehow got into the ckt. So overall, Pana didn't cut any corners.

OK, who wants to test it and see 

[cadman]

Just wanted to provide a follow-up. I ordered a Pana 308 and was pleasantly surprised at how quickly it showed up! Also, it's much larger than I had pictured it. I got a chance to play with it last night and I think I'm going to have some real fun with it.

Extension numbering on this one runs from 11 to 18. Also, just a tidbit for the archives in case anyone does a search and is curious. If you connect an extension to a CO port and dial that extension, all the phones will ring (as expected). Hanging up the phone you dialed from does not cancel this action, so the phone you dialed from will start ringing too! Picking up any extension will then unlatch the operation.

Now to wait for the ground to thaw and rent a trencher!

[twocvbloke]

If you connect an extension to a CO port and dial that extension, all the phones will ring (as expected). Hanging up the phone you dialed from does not cancel this action, so the phone you dialed from will start ringing too! Picking up any extension will then unlatch the operation.

Yep, I learned about that a few years ago on another forum, and when I finally got my 616 I had to try it, and it works great for demoing the ringers on phones, so I made up a jumper cable and labelled it as "Demo"...

Although I didn't learn about the "will continue to ring until any extension is answered" thing until I tried it, was rather disconcerting that the system just kept ringing when I'd hung up...

[Owain]

It should time out after a couple of internal rings once the external ringing ceases.

[G-Man]

It should time out after a couple of internal rings once the external ringing ceases.

As Owain stated it should time-out after several rings. It does the same thing when a regular central office call comes in and is not answered. The same thing happens with most 1A2 key systems.

[cadman]

I guess I'll have to try it again. I've got CO1 connected to the top extension port so perhaps the cycle time of ringing through all the extensions explains the lag.

With regards to ringing current sent back into an extension, I commented in another thread, but after looking at the schematics, when ring current is commanded out for an extension, a DP relay actually disconnects the internal circuitry, enables the ring voltage to the jack for a "two ring" duration, switches back to the internal ckt and checks for an off-hook condition, then repeats. So under typical ring voltage conditions, the components that could be damaged are kept out of circuit. However, there appear to be a couple of decent zener diodes on the talk ckts so I'm pretty sure they'd be ok if ring current was accidentally applied to an extension port.