View Full Version : For the electricians in the house...

Geremy Britton
02-21-2009, 08:48 AM
I've got a interphone used from a 747, it would be great to have the phone handset hooked up to a standard large phono socket so i could plug it into a speaker with a phono input, so it will sound my voice in the cockpit through the handset.

I've attached the pic of the pins of the phone and if anyone knows how you could wire specific pins upto getting the phone's voice mic to activate and output my voice when i talk into it to the external speaker with a phono socket that would be great.

I hope i make sense ... ask anything you're not sure on!

(P.S i've also attached a couple of pics on the korry indicators that are at the top of the phone module. Are korry's 24V ?)

Look forward to hearing your expertise in the electronics area as quite clearly mine is lacking!

Thanks again

Michael Carter
02-21-2009, 09:12 AM
I can't help out with the phone, but the Korry's are 28VDC. They operate fine and are plenty bright on 24VDC.

You'll probably have to take the phone apart and trace the wires to the internal components to figure out what makes it tick.

Geremy Britton
02-21-2009, 09:26 AM
cheers Mike, 24VDC it is.

And i'll try and see if i can open up the phone handset though it doesn't seem to want to open by pulling apart and i don't want to break it - i'll see what i can do.

Michael Carter
02-21-2009, 09:30 AM
Sometimes the Korry's are polarity sensitive and will have a diode inside. The usual wiring is terminal 1 & 3. Try the voltage on those terminals first. If it doesn't work that way, reverse the polarity.

And if that doesn't work, try the other terminals. These can be wired in many configurations, but there is usually a schematic right on the housing.

You have only half a Korry there. Do you have the other half too?

Geremy Britton
02-21-2009, 09:49 AM
Yes, i have the other half. The actual casing which is in the phone panel.

As from the pic, there are 2 wires attached to the Korry's on both terminal 3&5. So i should imagine this will be the 2 terminals here. But if that doesn't work even after switching polarity. I will try the terminal 1 to 3 approach (Pun not intended)

(And i can't see a schematic)

02-21-2009, 10:53 AM
I haven't seen one of these Interphones before, and it's a bit difficult to say without actually getting my hands on it, but I think you will probably have two possible options in getting it to do what you want:

Firstly, you could look at getting it to work as is - That is to say, you could identify the function of the pins in the Cannon plug and interface to that.

Or you could rewire it, and just use it as a mic by bringing the mic output out.
You may also consider that you don't want the mic live all the time - So you could probably use one of the buttons to enable it when you want to speak.

-If button has normally closed contacts, you could wire it such that there is normally a short across the mic which is removed when you press the button.

You could perhaps use another button to enable the call chime ?

How you get the audio out of your speaker depends on what amplifier/speaker setup you have at the moment.

The mic looks like a dynamic low level type - But it might incorporate some kind of amp - Could really do with sticking an oscilloscope across it to see what kind of level comes out of it, but failing that, trial and error is the way to go!

I'm guessing that when/if you find a way to get the thing apart, there will be an amplifier of some description in there to get the mic output up to line level.

Anyway, you might be able to take the mic output into a soundcard on your pc (screened cable) or you might need a little mixer/pre-amp to get the level up to drive something like an external powered pc speaker.

If you could get the thing apart and post a closeup photo of the internals/PCB if any, then we might be able to figure out how to interface to it as is, and take advantage of any onboard amp/audio line driver.

It's basically part of an intercom system, but how much of it is in the handset, and what is elsewhere in the aeroplane remains to be seen. There might also be some logic/data lines to handle the identification of the station depending on the topology of the system.

Judging by the large number of pins on the Cannon plug though, it looks like the complete station.

Cannon pins could possibly be:

Power Supply(2)
Audio In/Out(4)
Logic/Data/Switching (?)

If you can give me some more info, I think we could get it working.


Michael Carter
02-21-2009, 11:10 AM
Maybe this can be of some use:


Geremy Britton
02-21-2009, 05:48 PM
Thanks Mike, but i realy wouldn't know where to start with that diagram. Though someone else might and may help us get going.

Right, I've got everything apart. And there is quite a bit of electronics in there.

To basically describe, There is two sets of speaker wire that is holding the main electronics lump to the plastic frame of the phone. As you can see in the pic. 1 red and black to the top speaker and one red and black to the bottom. In amoungst the electronics also is the push button linked to the large light blue button entitles "Call" It would be great to somehow get the red and blue wired wired up to a large phono adapter which can be plugged into my speaker system which is like a small speaker purchased off a charity stall with a large phono adaptor on it. (Bit like a karaoke thing, that you'd plug a microphone into basically)

So yes, if we could wire the bottom speaker to a phono adapter to amplify what i say into the handset out of the speakers to the 'cabin' then that'd be great.

Furthermore putting the "CALL" button in series with this phono and speaker circuit so it only activates whilst it is depressed (The switch is a momentry switch though :()

Oh and correct me if i'm being too silly here but would it be possible to connect the top speaker with a red and black wire to another output, to maybe sound atc, or stewardess recording for example. Just for that added realism.

I'm counting on you Rob, and if anyone else can help - please chip in with any hints!

I've included high quality photos of most of the contents of the phone handset as you will be able to see. Looking at these photo's the above will become much more apparent.

Thanks again. When i bought the phone a couple of years ago now. I likes it so much i bought it for about 25 on ebay from Skyliner747 as some of you may know. I've never seen one since so i'm quite proud of it.

When purchased i intended it to be a 'museum' piece but i've been thinking i could do more. So here i am.

Your help would be eternally appreciated.


02-21-2009, 07:57 PM
For an easier and cheaper option, especially if you have no electronic knowledge as such consider...

You could always keep the outer shell and discard the 'guts' of the unit.
THen fit in an after market type intercom unit such as a motorcycle intercom I have seen advertised on the Net.


for a loud speaker effect, buy an old Cb radio with the PA output. Run the speaker and wires up through the unit so that you can speak and it will be amplified through the cabin.

02-21-2009, 08:28 PM
Sadly, the photos are a bit blurred, and not really close enough for me to tell too much apart from the degree of complexity.

Unless someone has a schematic or some expert knowledge then the chances of getting the original working remotely is practically nil.

Even if I had it on the bench here, I reckon it would take me a good while to trace into the circuit and work out the interface.

I think my approach to that would be to work from the Cannon plug, and find the supplies and the audio lines if any - If one could find supplies, then could power it up and hope to get some audio out.

It looks as if a fair amount of it could be digital, and that may apply to the audio too - In which case, not worthwhile proceding.

Your best bet may be to carefully remove the electronics, put them on one side somewhere, and just use the mic.

If you want to go that way, need to determine what type the existing mic is and if it's useable.

You might be better off taking out the lot, and fitting your own.

You will then have plenty of room in the handset.

Are you sure the amp you have, has a phono input - Or is it a 1/4" mono
jack ?

Generally, vocal mic inputs as used by karaoke machines are 1/4" jack to take relatively low impedance/low output mics.

So if you want to try the original mic, and it is a 1/4" input, I think the best thing for you to do is to desolder the wires and remove the mic from the H/S
(don't get it too hot- It looks like it could be easily damaged).

You could have a look and see if there is any manufacturer name and part no. first - Check the earpiece end as well.

If you have a multimeter with resistance range measure across it - If its in the order of hundreds of ohms then, it may work - If it's practically open circuit (megohms) then it is probably electret - Easier to replace it.

Get a 1/4" jack plug (if that's what it is) and solder a short length of open ended screened cable onto it. Plug it into your amp and see if you get lots of hum when you stick your finger on the centre conductor. If so, all well and good.

Solder the lead onto your H/S mic and see if you get any audio.

If it's ok, then put in a screened lead between handset and amp positions.

See if the curly lead has screened cores in it, if so, joint onto it in the cradle,
refit your mic and joint a short length of screened cable between the cores used in the curly lead and the mic.

wrt the switch:

You don't really want the switch in series (leaves cable open circuit = Lots pickup/hum) - Better to put the switch across the mic, so the cable is short circuited in the idle condition, and goes open when the switch is pressed - There may be a hook rest switch you could use for that in the cradle ?

In which case solder the screened and curly leads in parallel across the normally closed contacts of the h/r switch.

If you can leave the blue 'Call' button in situ, you could take a spare pair of wires from the curly lead to it, and then run a pair from the cradle to your IO card input and set it up to operate the Fwd Ovhd Attendant Call - Think Ian Sissons has done that with PMDG?

If it were me though, rather than use your little amp, I think I would consider using the same system as I use for cockpit sounds driven by the PC sound card - Some folks use home theatre/sound surround type audio systems - But I've just got a cheap hi-fi(?) stereo amp (Argos!) the mic could then be wired to the sound card mic input - That way you will get the chime as well.

Hope this helps,



Geremy Britton
02-21-2009, 08:41 PM
THanks for the Info Rob.

The ID plates says:

Dual attendant handset
MFR P/N 409D1600
SER NO. 905
LAC P/N 672767-107

And as you say, i may end up taking out the compnents and adding another phone inside or something. I'll think of something.

Though you'll have to explain the ARgos hifi thing.

I understand hooking the "Call" button up to FS via FSUIPC etc and that's a good idea. But don't understand the Hifo think for sounds. Sounds good though!

Thanks again for your details prompt reply on this.


02-21-2009, 09:49 PM
To get cockpit sound, I have a cheap hifi separate amp from Argos
for about 60 I think, and a cheap pair of speakers I picked up from one of the electrical superstores on offer - Can't remember how much, but it was less than 100.

The amp is an Acoustic solutions SP101 - It's not what I would call 'hi-fi' - But it is fine for the job - I play music through it from my PC as well, and it is quite listenable.

If you use a home-theatre type system with multi speakers, you can get a better rumble from the bass I think - Acoustic Solutions do a cheap one of those too - Have a look at Ians site, he talks about it there.

I have the amp connected to my PC sound card line out (3.5mm stereo jack to twin phonos) so that when you run FS you get all the cockpit sounds - Switch clicks, alerts, engine noise and so on - So when you hit the Attendant Call on the PMDG Fwd Ovhd, you will get the two tone chime.

Depending on your sound card, it should be possible to plug your interphone mic input into the card and set the mixer up to send your mic audio out on the line out - Mine does, and it's nothing special - Just the onboard sound from the motherboard.

If you wanted to liven up the earpiece on your handset you could simply tap off one of the speaker outputs via a resistor - About 4k7 depending on how loud you find you run your amp and assuming e/p impedance ~ 300 Ohm - That would give you background noise, and also sidetone (you hear your own speech at low level in the e/p when you talk into mic (like a telephone) - Sounds weird if it's just dead e/p).

Are there any identifying marks on the earpiece or mic themselves ?


02-22-2009, 04:43 AM
Blurry but the pix look like an old style 60HZ system.
Easiest way to hook it up would be to bypass the internals and just link the mic to a shielded cable going to a mini-PA amp. You can pick them up very cheaply in many places. A mini-guitar practice amp would be a good choice. They run about $30 in music stores.