Tommy Flowers Bletchley Park - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

David G4EBT · 17th Oct 2025, 6:19 pm

Interesting 1-Hr youtube video of a talk ‘Colossus - the Greatest Secret in the History of Computing ’ to the Centre For Computer History by a chap called Chris Shore about Colossus, Tommy Flowers and others. What a guy. Like others, by the nature of their roles, never credited for their closely-guarded achievements during their lifetime:

https://m.youtube.com/watch?si=MRjg02sxQShx30pO&v=g2tMcMQqSbA&feature=youtu.be

wireman · 17th Oct 2025, 7:29 pm

Images from a trip to Bletchley in 2008...

wireman · 17th Oct 2025, 7:30 pm

Final set...

Craig Sawyers · 17th Oct 2025, 10:50 pm

The SZ42 is the machine on the bottom row, 4th picture in. Completely working at that point. To the right of it is the correct Lorenz teletypewriter (with German keyboard) that would have been used with the SZ42.

There is also a tapereader to the left. So one operation mode was to use punched tape plain text links rather than the teletypewriter.

The four contact buttons on the top left connect to sprung contacts in the lid, for illumination bulbs so the rotors can be seen and set in subdued lighting. The bulbs were either missing or blown, so I replaced them, and left spares. It looks great either with or without the lid.

The other thing is the red switch at the bottom is labelled ein and aus (on and off). It doesn't switch the machine on and off. In the off position is unlocks the setting wheels, so each rotor can be set in the correct positions for the day, and camlets also set or unset for each wheel position. When switched on, the rotors all click round to a "start" position. Whir, clickety clickety...clunk, and the machine then is set to send and receive cipher text.

Craig

Craig Sawyers · 17th Oct 2025, 11:07 pm

The other thing worth pointing out is the large box just behind the emf cover. That is the limitations mechanism. Taking the box cover off reveals a switch to turn it off and on.

If on it further randomises the code. Basically it causes random stopping of the first 5 rotors depending on whether the first rotor returns a 0 or 1. It could only be used if the radio connection was low noise. So more often than not it was just turned off.

Craig

17th Oct 2025, 6:19 pm	#21
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 6,164	Re: Tommy Flowers Bletchley Park Interesting 1-Hr youtube video of a talk ‘Colossus - the Greatest Secret in the History of Computing ’ to the Centre For Computer History by a chap called Chris Shore about Colossus, Tommy Flowers and others. What a guy. Like others, by the nature of their roles, never credited for their closely-guarded achievements during their lifetime: https://m.youtube.com/watch?si=MRjg02sxQShx30pO&v=g2tMcMQqSbA&feature=youtu.be __________________ David. BVWS Member. G-QRP Club member 1339.

17th Oct 2025, 7:29 pm	#22
wireman Heptode Join Date: Feb 2021 Location: Edinburgh, Scotland, UK. Posts: 670	Re: Tommy Flowers Bletchley Park Images from a trip to Bletchley in 2008... Attached Thumbnails

17th Oct 2025, 7:30 pm	#23
wireman Heptode Join Date: Feb 2021 Location: Edinburgh, Scotland, UK. Posts: 670	Re: Tommy Flowers Bletchley Park Final set... Attached Thumbnails

17th Oct 2025, 10:50 pm	#24
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 5,840	Re: Tommy Flowers Bletchley Park The SZ42 is the machine on the bottom row, 4th picture in. Completely working at that point. To the right of it is the correct Lorenz teletypewriter (with German keyboard) that would have been used with the SZ42. There is also a tapereader to the left. So one operation mode was to use punched tape plain text links rather than the teletypewriter. The four contact buttons on the top left connect to sprung contacts in the lid, for illumination bulbs so the rotors can be seen and set in subdued lighting. The bulbs were either missing or blown, so I replaced them, and left spares. It looks great either with or without the lid. The other thing is the red switch at the bottom is labelled ein and aus (on and off). It doesn't switch the machine on and off. In the off position is unlocks the setting wheels, so each rotor can be set in the correct positions for the day, and camlets also set or unset for each wheel position. When switched on, the rotors all click round to a "start" position. Whir, clickety clickety...clunk, and the machine then is set to send and receive cipher text. Craig __________________ Doomed for a certain term to walk the night Last edited by Craig Sawyers; 17th Oct 2025 at 11:08 pm.

17th Oct 2025, 11:07 pm	#25
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 5,840	Re: Tommy Flowers Bletchley Park The other thing worth pointing out is the large box just behind the emf cover. That is the limitations mechanism. Taking the box cover off reveals a switch to turn it off and on. If on it further randomises the code. Basically it causes random stopping of the first 5 rotors depending on whether the first rotor returns a 0 or 1. It could only be used if the radio connection was low noise. So more often than not it was just turned off. Craig __________________ Doomed for a certain term to walk the night