TMC Modem from 1969, documentation wanted

[Roland Huisman]

Hello, recently I got this modem together with my Teletype 33 ASR.
The teletype had all PDP8/E modifications (currentloop to RS232) in it
and the documentation was inside the Teletype. (done by Geveke)

But this modem was also with the Teletype. There is not a single chip in it.
All discrete components. I think this is a 110 BAUD only modem.
But I can't find any info about it.

There are a lot English components in it, a few German capacitors and
some Philips components. But if it was built in Germany then the Germans
put German text on it and certainly not English text. And I can't find any
Dutch text in it. So my best guess is that it is made in England...

Almost all components are dated in 1969 and a few in 1968. So I expect that
it was made in 1969.

That 4 pin phone socket and the mains plug are typically Dutch. But these
might be not original placed by TMC.

Does anyone recognize this modem? And are there any schematics or other documents available?

Thanks in advance!
Regards, Roland

[TonyDuell]

TMC = Telephone Manufacturing Company (or something like that) I think and were related to Plessey.

The case was shared by a number of modems used by the British Post Office in the 1970s, such as the Modem 2B (300 baud). But the modules (and indeed the order they are fitted) are totally different. The bad news is that even though I am a member of the THG (and thus have access to documents that way) I have never found any technical information on any of these modems.

[Roland Huisman]

Hi TonyDuell,

Thanks for your response! So the TMC modem is English indeed.
I'm very curious to the other models. Are there any pictures online?

Too bad that there are no schematics available... And to be honest, I'm
afraid that this modem is just one of the few still in existence.
Maybe I will take the time to draw the schematic from the PCBs.

I would love to hook this thing up to one of my PDP8 systems
and establish some sort of serial connection to another machine...
Or are there still 110 BAUD BBS systems online ?

If anyone has more info about these TMC modems then I would love to hear it.

Regards, Roland

[electronicskip]

It looks almost identical to the TMC D200E 200 baud unit which was made under licence from the GPO.

[TonyDuell]

I've done some more searching in the THG member-only BT archives and found circuit diagrams for the power supply, control unit and modulator units (I can't find the demodulator). Unfortunately I am not allowed to send them to non-members of the THG, but it might be worth you joining that group to get those 3 diagrams (if you do so, let me know and I'll tell you exactly what to get).

Also, just looked at my old GPO modems. Apart from the plate on the right with the Dutch socket, etc, your unit looks identical (same modules, same order) to the old Modem 2B which was an originate/answer 300 baud (up to, will do 110 baud too) unit.

[Roland Huisman]

Hi TonyDuell,

Good to hear that there are schematics available! What is the THG?
I will sent you a PM. Maybe you can help me from there to get to the right website.

[TonyDuell]

Replied to your PM. And I've now found the demodulator diagram and an overall module-level diagram for the 2B at the same site. Unfortunately for you (and others) you have to be a member of the THG (Telecommunications Heritage Group) to access that site and I can't (legally) send you the diagrams.

[trobbins]

I have a TMC Low Distortion Oscillator, made circa 1967 in Australia, that I haven't located any documentation on. General history for TMC in links below. TMC was an Australian company registered from 1960 to 1985.

https://www.telephonecollecting.org/...es/TMC/TMC.htm
https://www.britishtelephones.com/histtr.htm
http://pepnet.org.uk/links/LinksPDF/EKCO%20Dpl.pdf

[John G8MWF]

Originally Posted by Roland Huisman

Hello, recently I got this modem together with my Teletype 33 ASR.
The teletype had all PDP8/E modifications (currentloop to RS232) in it
and the documentation was inside the Teletype. (done by Geveke)

But this modem was also with the Teletype. There is not a single chip in it.
All discrete components. I think this is a 110 BAUD only modem.
But I can't find any info about it.

There are a lot English components in it, a few German capacitors and
some Philips components. But if it was built in Germany then the Germans
put German text on it and certainly not English text. And I can't find any
Dutch text in it. So my best guess is that it is made in England...

Almost all components are dated in 1969 and a few in 1968. So I expect that
it was made in 1969.

That 4 pin phone socket and the mains plug are typically Dutch. But these
might be not original placed by TMC.

Does anyone recognize this modem? And are there any schematics or other documents available?

Thanks in advance!
Regards, Roland

Hello Roland,

I do not have any diagrams but I did work for PYE TMC Sevonoaks Way for a number of years starting in 1973 and recognize this product. It could just as easily have been made at a run in the Dulwich, Malmsbury or possibly Livingston factories.

The biggest problem are dirty edge connectors!!
They were certainly on the factory floor at that time.
Philips took over TMC and then AT&T took over the Philips telecoms sector of the company.

Most of those that I worked on were the leased line 4w 300 baud type - and it is a simple matter to loop them back on themselves to see if they work.

I would be interested to see how you get on with this project!

KR John

[John G8MWF]

just had a thought - can you show a picture of the labels located on the inside of the card handles - this may, if my memory starts up again, give me a clue as to the origin of the cards.