[GreenKeys] Information on Extel Printer.

[Sheldon Daitch]

 I am going to go out on a limb, as I am having to go from memory of things I knew more about, roughly 30 years ago.

If the Extel printer had an RCA logo on it, it was probably in UPI use.  UPI used RCA Service to maintain their equipment, while the AP tended to use in-house technical staff to keep their machines working.

The print head is seven pin, with a small electromagnet to drive that pin to print the portions of the completed printed item, as the print head stepped across the paper.

Any possibility the model is an AH-11R?

The AP Extels were generally loop current driven, as the AP had numerous Lenkurt 25A stand-alone single channel VF demodulators.

The UPI Extels were generally outfitted with a tone demodulator which was installed in the Extel case.  

Was this always the configuration?  Don't know.  Might have been what the AP or the UPI had on hand when a subscriber had an Extel installed.  

The xtal switch, as best as I remember, was to control the baudrate of the teleprinter itself.

The AH-11 series machines were manufactured in at least two versions.  One version did not have an automatic carriage return and if that machine ever missed the CR character, it would overprint at the end of the line until it received the next CR character.

Another version had an end of line electronic CR, in the event the system missed the CR character.  There were two metal contacts, one on each side of the typing mechanism.  If the print head hit the right hand contact, the system did a carriage return.   The electronics would buffer the print commands until the print head had moved to the left hand contact and was ready to print the next line.  There were no overprints of any characters while the print head moved back to the left margin position.

This buffer would hold about three lines of printing at the typical AP/UPI data rate.  It was interesting to see the Extel printer "catch up" with the printing, if the print head was kept from touching that left hand contact.  I discovered this little piece of trivia, when I noticed the Extel at one station where I worked, that the printer had a different speed for the first few letters of each new line.  One day, I kept the print head from hitting that left hand stop and realized there was a print buffer.

I am sure someone will let me know if I have anything wrong.  The memory tends to fade a bit.

73
Sheldon

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Bill Allen Jr
Sent: Monday, May 27, 2013 10:50 AM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] new list member and teleprinter question

Hi all,

i have an old teleprinter with an rca logo on the front that is sitting on an extel interface box.

the extel model is AN 11R 155

it was used with a upi or api wireline.

the interface has a crystal selector switch and i have no idea what that is for or why it used xtal's on wireline.

the printer is dot matrix but not 9 pin.

What two wire interface and protocol did this use?

i'm thinking eather 20 ma current loop or some odd subcarrier audio line.

anyone know?

Bill

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