Author Topic: My first payphone, Merk Tischmünzer 55  (Read 929 times)

Offline countryman

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My first payphone, Merk Tischmünzer 55
« on: December 13, 2020, 05:18:30 AM »
I could not resist when this popped up on eBay, a German "Teilnehmer-Münzfernsprecher 55b" made by Merk Telefonbau. Colloquially, these were called Tischmünzer or Ti-Mü. They were usually installed in restaurants and taverns to be used by the patrons. Two 10 Pfennig coins were placed on top of each other into the tray and a local call was made. When the called party answered, the tray was slided to the right and the money was encashed to enable the transmitter. Local calls would cost 20 Pfennig no matter of the duration until the early 1970ies.
The dial has a mechanism to prevent 0 or even 00 being dialed as the first numbers (for long distance or international calls) and the hookswitch is dampened to prevent tapping.
When a time limit for local calls was introduced, the Ti-Mü became obsolete. Moreover, there were hacks known to do long distance calls with them. But usually the innkeeper would have an eye what the guests were doing so that some may have been in use longer. The 10 Pfennig coin was called a "Groschen" in German (from an ancient currency unit) so this type of phone was nicknamed "Groschengrab" - groat grave.

I'm excited what will arrive. The phone is in rough condition and was priced accordingly. The vault seems to be open but I do not expect a key will come with it...

Auction link: https://www.ebay.de/itm/124472980630

Offline RB

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Re: My first payphone, Merk Tischmünzer 55
« Reply #1 on: December 13, 2020, 07:44:44 AM »
Interesting indeed!
Can't wait to see it cleaned up and smiling again!

Offline dsk

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Re: My first payphone, Merk Tischmünzer 55
« Reply #2 on: December 13, 2020, 11:20:23 AM »
I have one in working order :-)

dsk

Offline tubaman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #3 on: December 13, 2020, 02:25:05 PM »
Looks to be complete - just in need of some love.
I've looked at these before and they usually got for quite a bit of money, so hopefully you have done well.
 :)

Offline countryman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #4 on: December 18, 2020, 07:54:52 AM »
I saw dsk's thread about his pristine Ti-Mü after I started this one.
Here are some pics after a cleanup of mine. It came as ugly as seen in the auction, if I had hoped for a blurry camera lens of the seller. And the mix of lacquer splatters, glue and an undefined grey layer did not come off with conservative methods. I had to resort to paint stripper. The citrus product I use is not too strong and I had luck with preserving the original paint on earlier occasions. And so it was with this phone again. I then tried to polish the dull and roughened original black paint and found it could be rubbed with denatured alcohol, almost like chemical sanding Tenite! The result is far from perfect but I'm glad that it can remain original and needs not being repainted.
The phone is a mechanical marvel but it is complete and the main components seem to work as intended. I did not test it yet because the 7-strand dial cord was cut. I will resolder the ends.
@dsk you mentioned you made a key for yours? There are 2 cylinder locks with cross-slot cylinder keys made by Zeiss Ikon. Key blanks are no longer made but seem to be available NOS - what was your approach?

Offline countryman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #5 on: December 18, 2020, 08:03:07 AM »
More pics. One 10 Pf coin came inside the phone, the other one could be found in my house. Marks and Pfennigs were discontinued with the introduction of the Euro almost 19 years ago (Hm, really that long?). 10 Pf would be 5 cent today (€ or $ give or take). The coin validation is not really sophisticated but won't allow noticeable tolerances in diameter either.

Offline dsk

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Re: My first payphone, Merk Tischmünzer 55
« Reply #6 on: December 18, 2020, 09:52:33 AM »
I had an old lock Trioving 5075 an the key is equal, but longer.  To the lock on the side I got the original keys.

Regarding the coins, try 5 Euro-cent coins. The unit is not extremely accurate.
dsk

Offline Key2871

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Re: My first payphone, Merk Tischmünzer 55
« Reply #7 on: December 18, 2020, 11:17:42 AM »
That's a very cool phone, and that dial is very complex looking. Congrats on a very neat piece.
KEN

Offline HarrySmith

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Re: My first payphone, Merk Tischmünzer 55
« Reply #8 on: December 18, 2020, 01:40:20 PM »
What dial is that? It is definitely a very complex looking thing. At first glance it reminded me of a Strowger.
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline countryman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #9 on: December 18, 2020, 02:11:58 PM »
The actual pulse and shunting function is almost invisibly buried under the complex locking mechanism. What looks like a Strowger exchange is a system that prevents dialing the 0 as first number, or a combination of up to 3 first numbers to disallow long distance calls.
For Germany it was usually sufficient to exclude a leading 0 to limit the use to local calls.
When dialing the first number the upper plane of contacts moves to the respective position, with the second number the second plane and so forth. the excluded numbers or combinations of numbers can be programmed by soldering contact flags on the outside.
It's explained quite good in dsk's older thread linked above. He has even given spreadsheets which contacts to solder! I need to check that on my phone.
The dial seems to be dated 1970 while the phone is 1960. The dial was made by Hagenuk, while the phone is a Merk.
I now have repaired the dial cord and everything worked right away! I had not expected that, looking at the complex mechanism.
I'll have to do a little lockpicking next.

Offline Key2871

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Re: My first payphone, Merk Tischmünzer 55
« Reply #10 on: December 18, 2020, 03:34:51 PM »
So, if no money is put in the dial won't turn?
Is that what your saying?
That's actually a interesting way to prevent a call.
But wouldn't shutting the pulse contact be just as easy.
But that is a very interesting price of work.
Obviously never saw one before.
And to look at the set as a whole, it doesn't look to be that complex.
KEN

Offline countryman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #11 on: December 18, 2020, 04:03:48 PM »
In fact the pulse contacts are short circuited by the number exclusion logic. The dial turns, but a zero can't be dialed as the first digit.
Otherwise, a call can be made but the transmitter won't be enabled until the money is cashed.
The system had a number of imperfections:
-the owner (innkeeper) was charged by the tel. co when a patron misdialed, but dialed a valid number and the called party answered. In this case the caller would hang up without paying the money.
-it could be cheated by pulling the plug of the phone, and dialing any 3 digits. This would do nothing in the exchange, but activate the number exclusion system in the phone, which is purely mechanic and not electric. Then plug in and dial 0081xyz for time and temperature in Tokyo, just because you thought the innkeeper charged too much for the beer you had.
-with the introduction of a time limit for local calls in the mid 1970ies these phones became obsolete, because there was no time control for the 8 minutes interval.

These phones were really expensive and the owner could not make any money with them, as the charge cashed was exatly the amount that was billed by the tel. co. It was purely customer service to provide one. Unless a patron might come in for a call and have a drink with it...
« Last Edit: December 18, 2020, 04:11:23 PM by countryman »

Offline countryman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #12 on: December 25, 2020, 04:00:57 AM »
Picking the lock was not difficult. I just used a paper clip. The vault was open when the phone came so that I could apply a little torque on the latch with a finger while manipulating the pins.
Zeiss Ikon also made door locks with the same key profile, but much longer. I found such a lock with 2 keys. They are very long but will work. Once I had the lock picked it could be dismantled. I decided to use only 1 set of locking pins any more, on the flat side of the new key. So any such key will fit from now on. The 3 sets of leftover pins and springs will be stored in the phone.

Offline dsk

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Re: My first payphone, Merk Tischmünzer 55
« Reply #13 on: December 25, 2020, 05:02:25 AM »
Nice job!

Offline tubaman

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Re: My first payphone, Merk Tischmünzer 55
« Reply #14 on: December 25, 2020, 10:23:37 AM »
Looks great - you got a really good buy there as these usually seem to fetch over €100.
 :)