Author Topic: Panasonic PBX Power Supply Modification  (Read 5206 times)

Offline Phonesrfun

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Re: Panasonic PBX Power Supply Modification
« Reply #15 on: March 28, 2011, 03:33:35 PM »
Can one wire 500 type phones to work from battery?  WHat's the lowest voltage they will will recevie/talk on?

For a two-phone intercom, all you need is a battery in series with the two phones.  However, the reason a magneto phone was suggested is that a 500 has no way of ringing the other phone.  You cannot do that with just a battery.

A battery holder from Radio Shack that holds two 1.5 volt batteries is ideal for hooking 2 phones in series.  You only need three volts for it, and depending on the amount of usage, and the size of batteries used, it will last quite a long time.  For the longest life of batteries, you can get a battery holder for 2 size "D" cells.  3 volts is pretty much an ideal voltage in series over a short distance.  You askes what the lowest voltage is....  Well, since the smallest regular battery is usually 1.5 volts, that would also work, but you might find it too weak.  I suggest 3 volts.  The absolute value of the voltage is not really important in this case.  You could even use a 12-volt car battery, but that would be overkill.

But, like I mentioned above, without a separate source of ringing current, you will have to either agree on a schedule, bang on the pipe, shout out the window, or call them up on a regular phone or cell phone and have them meet you on the intercom.  You could also run a separate line for a buzzer circuit.

« Last Edit: March 28, 2011, 04:09:34 PM by Phonesrfun »
-Bill G

Offline trainman

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Re: Panasonic PBX Power Supply Modification
« Reply #16 on: April 02, 2011, 01:27:43 AM »
Hi all, thanks for the suggestions.

I think I'll look for a couple of workable mgneto phones for the "phone system"

Offline GG

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Re: Panasonic PBX Power Supply Modification
« Reply #17 on: April 02, 2011, 07:31:48 AM »

The Micro Seven has the interesting feature of an amplitude and frequency adjustment for the ringing, from little screw type trimming resistors accessible via holes in the bottom of the unit.

Yes that means you could use a bunch of phones with harmonic (frequency selective) ringers, as long as they were all the same frequency (good luck! : - )

Though, some of those are selling for prices that'll get you a Panasonic, new.


The two-way ringdown circuit thing shows a label by the power cord saying it uses 30 watts.  That's more than a Panasonic PBX and for what it does, it's an energy hog if you leave it plugged in all the time. 


Re. 500 sets as intercoms:  Another cheesy phone mod I used to do in highschool was to turn these into common-buzz intercoms as follows (it's been @ > 30 years since I did these so this is from memory and may not be correct):

Attach an Edwards DC buzzer from L2 to G, where the red & black wires from the C4A ringer are connected.

Wire across F and RR to jump the dial pulse contacts.

Take the white (off-normal) dial contacts and wire them across L1 and G. 

Connect all the phones together using 3-conductor wire: all the L1s together, all the L2s together, all the Gs together.

Connect a DC source sufficient to buzz all the buzzers, across L1 and L2. 

Now when you turn the dial, it connects DC to the buzzers and all the phones buzz, for common signalling and common talking. 

Assign different buzz codes to each phone.  Typical would be a 4-station system with:  Short-Short, Short-Long, Long-Short, Long-Long.  Dial a low digit such as 2 for a short buzz, and a high digit such as 8 for a long buzz. 

A system like this works well for e.g. a household of four people, because you give buzz codes to the people rather than the phones, and the people can answer from anywhere.   E.g. Alice = Short-Short, Bob = Short-Long, etc.  To get more than four people, use three buzzes, e.g. Short-Short-Long, etc.

And of course all the cheesy phone mods can be undone and the phones put back to being regular 500 sets any time. 


Alternately, AE 87 or 187 sets, with the little Signal button, can be used nicely for 2-line sets with the 3d line used as Intercom with non-selective buzz.  With DC buzzers, this adds up to seven wires, which will run on 4-pair and you can use Ethernet plugs & jacks to make it easy to do. 

The problem nowadays is finding "nice sounding" DC buzzers that are telco quality, and ideally that are small enough to fit inside the telephone sets.  Alternately one can use a 5-wire circuit for intercom, whereby two wires are DC for talking, and 3 wires are AC for running those little round 1A2 station buzzers, which are telco quality and nice sounding (for buzzers anyway, heh)   However, a 5-wire intercom circuit means that two lines + intercom = 9 wires, thus can't be accommodated on 4-pair. 


iMHO for residential use for households up to @ 4 people, common talk & common signal makes the most sense.  You want to talk with Bob who could be in his bedroom or in the living room or somewhere else.  You don't want to call his bedroom and then call the living room and ask Alice who is in the living room where Bob is and then she says you need to call the garage because he's working on something out there and blah blah blah...   Faster to just press the little signal button once long and once short, and then Bob answers and says "I'm in the bathroom, I just got out of the shower," thereby proving the age-old rule that the surest way to make the phone ring is to go to the bathroom or be washing dishes with your hands all full of soap suds. 

Offline GG

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Re: Panasonic PBX Power Supply Modification
« Reply #18 on: April 02, 2011, 08:03:11 AM »

How to use a Panasonic PBX for "calling by person rather than by room":

Hook up external paging speakers.  There are self-amplified types that run on 2-pair, where one pair is audio and the other is common 24 vDC power, Valcom make these. 

There are also desk speakers that look a little like oldschool radios without tuning knobs.  If they make 'em in red, you can pretend you're living in North Korea and that's the obligatory 1-channel government propaganda feed ; - )

Dial the "page code" to page through all the speakers, telling the person you want to reach to pick up any phone and dial the "page answer code."   When you dial the page code, the speakers go beep-beep and then you can talk over the speakers.  For example, "Alice, dial 123" (or whatever the code is).  The person you're calling goes to the nearest phone and dials the page answer code, and they're connected to you. 

You may have to tweak the numbering plan to get rid of the pesky * at the beginning of most of the feature codes, and shorten the dialing codes for the things you use most often such as page and page-answer. 

If there's demand around here for these, I could start providing them: new Panasonic systems with numbering plans tweaked appropriately for dial phones.  (I've been saying for the last couple of months that I'd post a price list for Panasonic PBXs, and the 1st Quarter insane workload is almost over so I should be getting to this soon.)  (Tonight I've been posting here while remote-programming new extensions for a client that's been growing by batches of 25 phones at a time.  Four more voicemail boxes to go...)  (Eric, I still haven't forgotten your AE speakerphone; I'll get it packed this weekend and ship next week.)