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T lab 340
Speed error recorder - not in collection

T-lab-340 was a speed error recorder (German: Drehzahlfehlerschreiber) for 5-level teleprinter signals (telex), developed around 1943 by Siemens & Halske in Germany. It was intended for the alignment of Siemens (and other) teleprinters, and featured a HELLSCHREIBER paper strip printer.

The devcide is housed in a standard panzerholz case with a removable lid at the front, common to the equipment cases that were used by the German Wehrmacht 1 during WWII. It measures 34 x 22 x 23 cm and weight approx. 14.5 kg.

The T-lab-340 was intended for recording errors in the speed, measured in Rotations Per Minute (RPM), of a teleprinter. This was done by writing (printing) the 5-level groups (bits) to a paper strip by means of a helix spindle print head. The latter was developed by Rudolf Hell and was also used at the heart of the famous Hellschreiber.
T-lab-340 prototype

The internal speed of the device was carefully calibrated to match the speed of a teleprinter. As the Hellschreiber - by design - prints an unsynchronised image, the image will be sloped (i.e. running off the paper) when the speed of the teleprinter does not match that of the T-lab-340. The device shown here, has the identification 'T lab entw 340 a' - 1934 engraved on its model plate, which means that it is a prototype 1 developed during World War II. It is currently unknown whether the design ever passed the prototype stage and, if so, how many devices were produced.

  1. Wehrmacht was the name of the German Army before and during WWII.
  2. 'entw' is the abbreviation of the German word Entwicklung (Development).

With cover in place T-lab-340 prototype Front view Front panel HELL printer Printer detail Output paper strip Stroboscope disc
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With cover in place
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T-lab-340 prototype
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Front view
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Front panel
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HELL printer
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Printer detail
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Output paper strip
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Stroboscope disc

All controls and connections of the T-lab-340 are located at the front panel of the device. When not in use, they are covered by a protective removable lid. The device is powered from the 220V AC mains, for which a fixed cable is present. The teleprinter line is connected at the bottom right.

The black unit at the left is the printer, which is similar to that of a Feldhellschreiber. Paper is fed in from the right, past the printhead and then between the capstan and a pinch roller, leaving the device on the left. Before printing, the arm with the ink roller should be lowered, so that it comes in contact with the helix printhead. A strong electromagnet, located in the rectangular black unit, pushes the paper upwards against the printhead, in the rythm of the 5-level pulses. This results in a series of dots (pixels) on the paper strip, representing the 5-bit baudot characters in time.

  1. Bernd Rothe, T-lab-entw-340-a restoration
    April 2013.

  2. Frank Dörenberg, HELL telex tester
    Retrieved May 2017.
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Crypto Museum. Created: Friday 26 May 2017. Last changed: Thursday, 12 October 2017 - 16:17 CET.
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