Heemaf 1955 intercom version

[unbeldi]

That's a nice story to be able to tell.

Do you have any ideas how many of these still exist?

I have plans for building a signaling decoder for that dial.
The functioning is not difficult to understand.

[Matilo Telephones]

Thanks.

I find it difficult to take a guess at the number left. I saw only 4 in the last 8 years on our local "Ebay" (marktplaats).
I know of 3 collectors who have one pictured on their website, 2 of them damaged. The other one is one that collector traded with me. :-)

Do you have one too? I have no idea how many were exported by Philips.

[unbeldi]

Thanks.

I find it difficult to take a guess at the number left. I saw only 4 in the last 8 years on our local "Ebay" (marktplaats).
I know of 3 collectors who have one pictured on their website, 2 of them damaged. The other one is one that collector traded with me. :-)

Do you have one too? I have no idea how many were exported by Philips.

Yes, mine is mounted in the wall phone though.  You are forgetting that we did discuss some of this before, but it never hurts to reminisce about common interests.

http://www.classicrotaryphones.com/forum/index.php?topic=10534.0




Of course my Heemaf collection is of beginners' size for Dutch standards, but I do pride myself of the Philips wall GDK. I have never seen another, and it does appear to be original, as it has a Philips label inside.

[Matilo Telephones]

Yes, I do remember that conversation. Rereading it now, I see we discussed Heemaf 55s more in deapth than I remember.

Still your wall version GDK is the only wall version I ever saw. And I am still very jealous.

Earlier this year I was in the depot at our Museum of Communication. They have a very comprehensive collection of Dutch telephones. I took pictures of every H55 variant they had. I'll check these pictures later, because I think even they did not have that one.

They did have a transparant wall and desk H55. Wow!

[unbeldi]

The wall phone came to me already mounted on the board, very nicely done. But I cannot remove it without damaging the mounting board or the pegs that are cemented into the wood.  Clearly someone did a very nice job. However, I would love to see the rear of the unit, perhaps there are additional markings.

I won it in an eBay auction, and I was nervous in the last seconds because I knew that I HAD to have this unit. But I was the only bidder in the end, and I got it for something like $16, shipping was more because of the size of the board.  The seller was not a collector, but a general seller of estate items.

Here is the diagram glued to the inside.  It shows the Philips logo. Their model number is NF000.12, without the Aardtoets.  The diagram does not show the GDK dial, so it was delivered as a rotary instrument originally, and it leaves one guessing when and by whom the key dial was installed. It is installed correctly though, so it appears perfectly genuine.

[unbeldi]

Here are some pictures of one of the PABX systems that our GDK telephones would have been connected to, I think.

http://www.actw.nl/Oude%20centrales/UB49a.htm

There is even another version of the dial, this one arranged in a more conventional keypad layout, definitely created a few years after our Heemaf types.

[Matilo Telephones]

Yes, that is the exchange I am looking for. :-)

I´d love to connect up one of my GDK´s and see what it actually does.

I googled an article about it once, written by 2 Philips engineers. It was a PDF. I did not download it and I cannot find it anymore. Sigh.

Remco Eindhoven is one of the keepers of that collection, by the way. He is a member of this forum.

Here are the pics of the H55 variants I took when I was at the museum.

I can show you how the back of your wall GDK looks like, if you like. I have a dial Philips H55, which should look similar. I´ll take some pics later.

Interesting that your diagram is in English only. I think the ones I saw were in 2 languages, English or Dutch is not always one of them.

[Matilo Telephones]

Since you have plans to make a signalling decoder, do you know how that GDK dial works?

I have tried to make some measurements with my volt/ampere meter. What do the buttons do? Change resistance?

[unbeldi]

Woah,  a clear wall version even.  They must have created that for a world fair exhibit or something special... the birthday of the Queen.

Thanks for the pictures.

Yes, I do understand the operation of the dial.  In summary, it consists of a set of four diodes which are switched in addition to two straight connections from ground to either line a or line b by the push buttons. While a button is pressed, the digit register in the PABX tests the condition of both lines sides with respect to ground by reversing the polarity on each with relays.  Since diodes only conduct direct current in one direction, the push buttons present a certain closure pattern (key code) which is stored in four register relays. Since a relay has two states, up to 4²=16 code patterns can be signaled, if the dial had that many keys.

So, the dial is entirely digital !

Attached is my working diagram of operation. The dial is the set of six switches in the lower left hand side. These six switches (4 diodes and 2 shorts) are activated by the buttons as indicated by the small numbers, in a clever combination of contacts.

The paper explains the operation pretty well, file attached.
B.H. Geels, N. Scheffer, Keyset Selection of Telephone Numbers, Philips Telecommunication Review Vol 17(1), August 1956, p.30-37

[unbeldi]

The only aspect I am unclear about with respect to the operation of my dial is whether my dial (or any working dial from production) is actually encoded in the exact same manner as the paper presents it. I tried to measure the pattern with an ohmmeter, but have some doubt about it and the only way to be certain is to unsolder some connections on the dial to sort it out and I don't want to do that.

It will be much easier to determine this when I have a working decoding circuit, as I will simply get a different assignment of key codes out of the dial and can just reorder the 'bits' out of the decoder.

[Matilo Telephones]

Thanks very much for that file! That was the article I once read and could not find again. Great. Downloaded it and saved it.

The clear wall version has a papar label hanging on it saying Dir Generaal der PTT (director general of PTT) jan 1957.

I think it was presented to him as a gift, possibly from Heemaf.

Interesting about the working of that dial. I have quite basic electronic knowledge and couldn't make heads or tails of it before. I understand it a little better now.

[unbeldi]

Thanks very much for that file! That was the article I once read and could not find again. Great. Downloaded it and saved it.

You're welcome.  I hope some day we can call each other with these push buttons.

The clear wall version has a papar label hanging on it saying Dir Generaal der PTT (director general of PTT) jan 1957.

I think it was presented to him as a gift, possibly from Heemaf.

Interesting about the working of that dial. I have quite basic electronic knowledge and couldn't make heads or tails of it before. I understand it a little better now.

I have a complete resistance chart for all key presses of the dial, in case you have done something similar.  It's a total of 12x6=72 measurements.  I measured resistance in two directions (swapping ohmmeter leads) between two each of the 3 dial leads, red (a), blue (b), green (ground).  The yellow lead has a simple switch which is not used in digit encoding, but disconnects the phone itself (breaks the loop) to signal the exchange that a key has been pressed and therefore a digit is available and must be read.

[Matilo Telephones]

That would be a grand and historic occasion. I think I would invite the Museum and the Holec Historic Soc to come and watch it. :-)

I have not taken the resistance measurements. I guessed that would be a factor, but I do not have an Ohm-meter yet. (Holding out for a vintage PTT meter).