Cypher machines maintenance and restoration spanning sixty years

Cryptologia, Jul 2003 by Clarkson, Dorothy

A number of specially modified Typex machines were used at Bletchley Park during the war for the routine decoding of German messages once the initial settings had been determined by the code breakers.

Following completion of the work on the Typex machines I was invited to participate in the restoration of one of the Museum's most valuable exhibits, the Lorenz SZ42 cypher machine, in collaboration with Dr. Craig Sawyers, an electronics engineer with a keen interest in and some knowledge of the machine.

We began work in the second week of October 2000 and initial inspection revealed the following:

1. The cryptographic unit, in its gasket-sealed box, was in excellent condition, the lubricating grease still soft and when the drive gear was operated manually appeared to be working perfectly.

2. The top layer of the main chassis appeared to be complete and in good condition but rather dirty.

3. Under the top layer all components and wiring were as new.

4. The power supplies, under the base casting, were a disaster area. The cover plate had obviously been missing for a long time and there was damage, both mechanical and as a result of exposure to damp resulting in the chassis being covered with a white powdery substance. Some of the wiring appeared suspect.

As the only information available was the article by Donald Davies (Cryptologia, Volume XIX Number 1, January 1995) it was decided that the first priority was a full survey of the wiring. This was carried out and between us we produced wiring data sheets (point-to-point connections) and circuit diagrams and found that in fact only a few connections on the power supplies required replacing, all other wiring being fully serviceable.

The main transformer, selenium rectifiers and capacitors were unserviceable but after much searching Craig discovered companies that were able and willing to manufacture exact replicas of the transformer and rectifiers and what's more, to do some of the work for free as a contribution to the work of the Museum. Craig himself restored the capacitors by fitting modern components inside the original cans.

Unfortunately, from the beginning of November I was incapacitated for twelve weeks following surgery on my left foot, leaving Craig to do all the hard work of stripping, cleaning and re-assembly so that by the time I returned at the beginning of February 2001 he was in the last stages of setting up.

We then located, in one of the Museum's store rooms, a dirty and dusty Lorenz teletype machine (a Springschreiber Type T32 Lo) which, despite its initial unpromising appearance, after a thorough clean came up looking almost new. Craig then built a small interconnecting unit which enabled the T32 to control the SZ42 and print cut whatever was typed in and the combination was successfully demonstrated to a group of visitors on 8th March 2001.

The following week I started work on the Siemens-Halske T52E cypher machine. I suspect that this machine had been stored in the same location as the Lorenz, the general condition being very similar - dirty, no base cover plate and a similar level of corrosion. The hinged cover for the relay unit was missing. Fortunately there was no sign of mechanical damage other than to the plug on the flying lead which was shattered.