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MkVII Camera

Page history last edited by David Samways 5 years, 11 months ago Saved with comment

 

 

 

 

 

In about 1963/4 Marconi had been tasked with providing equipment to be demonstrated to the EBU and CCIR at BBC Lime Grove Studios to help in the work of choosing the European colour standards. This mainly addressed the NTSC / PAL / SECAM debate. A further demonstration at GEC headquarters in the Strand showed RYB and four tube camera variants. The team felt that the four tube design had not been a popular one and there was some surprise when the company asked the labs to begin the design of one. With such a design

 

The fourth tube provides the brightness / detail signal (Luminance Signal).  The decision to go this way was possibly related to difficulties in getting the individual images to overlay accurately (register). Whether or not this was so I am unsure and it is rather late to re-judge the plan now. However I will note that we were the only manufacturer to go along this route and the use of an extra tube gave us nearly a 30% cost disadvantage compared with the others.  The camera tube for this design would be the Phillips 30mm diameter Plumbicon (see photo); the design was later duplicated by what is now E2V (English Electric Valve) and called Leddicon. The design of this tube, which used a lead-oxide photosensitive layer, was much simpler when compared with the image orthicon but the sharpness (resolution) was considerably less. Significant image enhancement would be needed to achieve the Broadcast Standards. We had only ever seen one of the tubes at the start of the project so it would be a steep learning curve. The camera, called the Marconi Mark VII (see photo) would have a zoom lens rather than the turret system that had been the norm previously.

 

My task in the project was to design all the video circuitry except for that in the camera head. It is worth noting that the complete system included a substantial set of 19” rack mounted units; this is where my bit would be housed. The design would be entirely transistor based with the exception of the very first amplifier element which would be a tiny valve (Nuvistor, see photo).  Transistors were in general a great advance in that they were much smaller than valves and didn’t need to be heated to make them work. However there were one or two functions where valves would have done the job better. Eventually, a year or so later, a new type of transistor (FET) became available and this gap was largely filled. Undertaking your first real design is an experience. The piece of paper is totally blank, you have the pencil / pen in your hand but what do you do next? I did, of course, know the necessary theory but I had virtually no design experience. Add to this the fact that none of the team had ever undertaken a transistor based design and you can see possible problems looming. Actually I did not find the task that daunting, obviously there were difficulties and a number of attempts were needed to reach a good solution. I came up with a few novel solutions that I was quite proud of and used these for further designs. The design for colour operation must be accurate and stable over a temperature range of about 20 deg C. If it drifts the picture may get a noticeable colour cast and the camera might not pass the stringent tests that prove it is fit to be used for transmission. A LOT of testing is therefore needed.

 

By the time the Mark VII project got underway all the TV development and installation staff had moved to the purpose built set of labs in Waterhouse Lane Chelmsford, these used to be on the other side of E2V, i.e. where Homebase is today. Here we had a proper studio area and this was used for the launch of the new camera. Engineers from the TV stations around the world were invited and we did our best to impress, with Judith Chalmers’ assistance. The photo (sorry about the quality) shows the ‘bar’ area of our studio with the Divisional Manager and our Engineering Manager ‘barman’ (Norman Parker-Smith) who is obviously enjoying the experience. When people like that appear it is a sign that the hard work is finished; well for the moment that is. Sadly the workers did not get a chance to talk to her. The camera was quite well received and the first production batch was soon spoken for. However, ITV in UK were slow off the mark and there were none to be had when they eventually got to asking for one. Could we not help somehow, they asked.  We let them have the somewhat tatty prototype and I was sent to ABC at Teddington Lock (I think it was ABC, they later moved into town and became LWT) to set it to work.  To be honest the camera was a bit of mess but eventually we reached a mutually acceptable point.

 

If you watched the Black and White Minstrel Show in the early 70’s you will have seen the results of our efforts. Obviously the MKVII was used for other shows but I can’t say which ones.

 

Scottish TV (STV) were one of earlier customers and I had to do some hand holding for the first night of colour. STV only had one video tape recorder (VTR) to cover both Edinburgh and Glasgow. The VTR was in Glasgow and we were in Edinburgh with the cameras. Unfortunately there was some problem on the line and the colour was lost; the grand opening went out in black and white; Oh dear! 

 

 

Further information

 

Specification for the B3205 MkVII colour camera channel available here

 

Brochure for the B3205 MkVIIB colour camera channel available here

 

Datsheet courtesy of the UK Museum of the Broadcast Television Camera available here.

 

BBC R & D Report - Measurement of the optical system in the MkVII camera click here

 

An article entitled "The MkVII - one year later" - by W.T. Underhill 1967 click here

 

An article entitled "The MkVII colour camera - the camera in relation to the system" by N.N. Parker-Smith 1967 click here

 

An article entitled "Vertical aperture correction for the MkVII camera" by A.N. Heightman 1967 click here 

 

An article entitled "Colour television cameras - the designer's choice" by N.N. Parker-Smith click here

 

 

 

 

 

 

 

Comments (2)

Philip Doughty said

at 8:18 pm on Dec 3, 2014

David - interesting article especially (for me anyway) about the early days of Waterhouse Lane - I noticed a couple of typos I think - in the first paragraph I think it should be RGB instead of RYB (unless RYB was in use for cameras and it's just that I've not heard of it) and the word 'latter' should be 'later' - thanks for putting all this information on the site it's great to see old photos of the cameras and of Waterhouse Lane
Phil

David Samways said

at 5:01 am on Dec 4, 2014

Thanks Phil, I have made one change. In the case of RYB I am asking the author Andrew Fremont, or somebody else more qualified than me, to respond to this comment.

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