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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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9th Oct 2006, 10:04 pm | #1 |
Heptode
Join Date: Jul 2003
Location: North Walsham, Norfolk, UK.
Posts: 516
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7BP7 flying spot scanner project
Hi
I've been toying with the flying spot scanner idea for a while, and have started with the scanner. My first plan was to make it all myself from scratch, but as I had a spare Bush chassis, I converted this for the scanner. The old PT mag did an article about the 931A multiplier tube and its insensitive to yellow, so the afterglow won't matter. But this is hardly noticeable anyway; only from rapid bright to dark on a TV picture. The next bit will be the photomultiplier preamp and power supply. Has anyone got a spare anode cap for a 7BP7 tube as I think the croc clip may start brushing on damp days? Also has anyone got any diagrams for flying spot scanners? I will still need a master sync genny, so any ideas would be fab. Thanks Danny |
10th Oct 2006, 7:14 am | #2 |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: 7bp7 flying spot scanner project
I am sorry to tell you that a P7 will give a very bad resolution in a flying spot scanner. Maybe a blue filter helps.
Kind regards, Darius |
10th Oct 2006, 7:35 am | #3 | |
Retired Dormant Member
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
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Re: 7bp7 flying spot scanner project
Quote:
The BATC has published a fair bit about flying spot scanning in its magazine CQ-TV. Mainly in the earlier days fo the club. Some of this is available online, the rest is available on a CD to buy. http://www.batc.org.uk http://www.cq-tv.com/ I think I wrote an article in CQ-TV many years ago about using an EVR player as a flying spot slide scanner. EVR was an ill fated domestic video replay system using special film. |
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10th Oct 2006, 5:22 pm | #4 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,517
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Re: 7bp7 flying spot scanner project
Looks like fun - I still have a few tubes here........
Damn - another project! Cheers Sean
__________________
Engineers make things work and have spare bits when finished |
10th Oct 2006, 10:01 pm | #5 |
Heptode
Join Date: Jul 2003
Location: North Walsham, Norfolk, UK.
Posts: 516
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Re: 7bp7 flying spot scanner project
Hi
Thanks for the links, Jeffrey. Looks interesting - there is a mention of the 5BP7 in there; it's also used in the PT articles of July 54 and Nov 54. Thay say 3meg is possible, so I will keep this tube in at the moment. There is also on one of the sites I visited, a suggestion of using a blue filter as Darius has also suggested as a possible help with the afterglow. Thanks Danny |
11th Oct 2006, 9:13 am | #6 |
Retired Dormant Member
Join Date: Feb 2005
Location: Stroud, Gloucestershire, UK.
Posts: 57
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Re: 7bp7 flying spot scanner project
I used 7BP7's for flying spot scanners, they work fine because you run them at a low beam current to minimise the spot size and at low levels the long persistance phosphor does not appear to be excited, conversly when I used a 7BP7 as a slow scan receiver you need loads of beam current to get any usable afterglow!!
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11th Oct 2006, 10:41 am | #7 |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: 7bp7 flying spot scanner project
Hi, for SSTV it is no problem because the spot goes slow. fh=16Hz.
But for fh=10000Hz or more the persistance is tooooo long. Darius |
11th Oct 2006, 1:22 pm | #8 | |
Retired Dormant Member
Join Date: Apr 2005
Location: Reading, Berkshire, UK.
Posts: 95
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Re: 7bp7 flying spot scanner project
Quote:
Afterglow has always been a problem and required around seven different time constant correctors for each channel. Even then you could see noise patterns produced by the whole process. Normal CRT's with a white output are not really suitable for flying spot work, as the phosphor is a mix of different phosphors, each with its own decay characteristics, which makes it impossible to get rid of all the afterglows. The photomultiplier you are using does have a peak response in the high blue range. But it will still have some output at other wavelengths. So you might have to use some optical filtering. My concern is that the CRT that you want to use has little output in the blue part of the spectrum and the signal to noise ratio isn't going to be good. Trish |
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11th Oct 2006, 1:33 pm | #9 | |
Retired Dormant Member
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
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Re: 7bp7 flying spot scanner project
Motorola? http://www.labguysworld.com/Motorola_EVR.htm
Or RCA/CBS? http://www.cedmagic.com/history/cbs-evr.html I think my EVR machines were made by another company, possibly Hitachi. Quote:
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