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Post by Deleted on Apr 25, 2015 16:54:16 GMT
Hi Alan ,
Quite a long time ago I read of a group making mechanical television systems . They were getting surprisingly good results . Seem to have disappeared now - ever heard of them in recent times ???
MichaelW
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Apr 25, 2015 17:00:27 GMT
Personally I seem to have little time for anything at the moment. Work is hectic, building and installing a number of level crossings, in addition home life and other things are conspiring to leave me with little time for anything. As with most things these circumstances will change giving me more time for other things.
Having spent about 10 years testing vehicles for the MOD it is no surprise that the Landrover owners are devoting a lot of time getting them to work and keeping them going leaving little time for ME activity.
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jem
Elder Statesman
Posts: 1,065
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Post by jem on Apr 25, 2015 17:17:39 GMT
Don't worry, when you retire you will find that you have even less time, or that is how it seems to me.
Jem
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Post by alanstepney on Apr 25, 2015 19:32:12 GMT
Hi Alan , Quite a long time ago I read of a group making mechanical television systems . They were getting surprisingly good results . Seem to have disappeared now - ever heard of them in recent times MichaelW Yes, AFAIK they are members of the British Vintage Wireless Society, as am I, so I can find out more if you wish. I dont have anything to do with televisions, and my main interest is collecting valves, of which I have some 8,500. That and restoring old radios. Makes a change from steam engines.
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Post by Deleted on Apr 25, 2015 19:49:20 GMT
Thanks for that .
I believe that they started making replica Baird ones but found that they could be developed much further than expected .
Incidently Baird's field sequential colour system actually got used on the moon landings though in an all electronic camera .
MichaelW
PS: Talking of valves : When I was a very young teenager the Wenvoe colour TV transmitters came on line for the first time and there was a series of open days . Final power amplification was by valves - absolute monsters of valves . They had that rather frightening crackling sound , blue glow and ozone smell always associated with high power systems .
One of the pet demonstrations there was to light an unconnected neon tube OUTSIDE the amplifier building .
I don't know what the transmitted power was numerically but there was certainly lots of it !
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Post by ejparrott on Apr 26, 2015 8:17:04 GMT
Having spent about 10 years testing vehicles for the MOD it is no surprise that the Landrover owners are devoting a lot of time getting them to work and keeping them going leaving little time for ME activity. Yes......got a gearbox sprung a leak again...guess it's time I got the spare out and rebuilt it again....
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Post by vulcanbomber on Apr 26, 2015 8:38:48 GMT
Having spent about 10 years testing vehicles for the MOD it is no surprise that the Landrover owners are devoting a lot of time getting them to work and keeping them going leaving little time for ME activity. Yes......got a gearbox sprung a leak again...guess it's time I got the spare out and rebuilt it again.... Joined in with that my 110 had one 3 fitted doors and the front wings not attached at the minute and the Discovery needs new sills and front inner wings... So yes finding time for the 9F is proving hard to come by. That and a 2 year old running riot and it's brother/sister on its way and a garden to sort out its somewhat difficult at the minute.
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Tony K
Elder Statesman
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Post by Tony K on Apr 26, 2015 8:58:23 GMT
PS: Talking of valves : When I was a very young teenager the Wenvoe colour TV transmitters came on line for the first time and there was a series of open days . Final power amplification was by valves - absolute monsters of valves . They had that rather frightening crackling sound , blue glow and ozone smell always associated with high power systems. One of the pet demonstrations there was to light an unconnected neon tube OUTSIDE the amplifier building. I don't know what the transmitted power was numerically but there was certainly lots of it! I spent all my working life in broadcast transmitting stations, working at near-enough all the high power transmitters in the UK and many of the smaller ones also. Perhaps this was one of the open days you went to - a silent film though, but in colour. Not being able to switch off the lights was quite common. One of the better demonstrations of broadcast power flashing over is the long wave site at Droitwich during an electrical storm.
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Post by Deleted on Apr 26, 2015 10:12:13 GMT
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Post by Deleted on Apr 26, 2015 10:16:23 GMT
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Post by Deleted on Apr 26, 2015 11:26:39 GMT
PS: Talking of valves : When I was a very young teenager the Wenvoe colour TV transmitters came on line for the first time and there was a series of open days . Final power amplification was by valves - absolute monsters of valves . They had that rather frightening crackling sound , blue glow and ozone smell always associated with high power systems. One of the pet demonstrations there was to light an unconnected neon tube OUTSIDE the amplifier building. I don't know what the transmitted power was numerically but there was certainly lots of it! I spent all my working life in broadcast transmitting stations, working at near-enough all the high power transmitters in the UK and many of the smaller ones also. Perhaps this was one of the open days you went to - a silent film though, but in colour. Not being able to switch off the lights was quite common. One of the better demonstrations of broadcast power flashing over is the long wave site at Droitwich during an electrical storm. Many thanks for that clip - right place and right time . Very nostalgic for me . See the size of the crowds though - quite ordinary people were fascinated by technology in those days . The sixties were very exiting times for science and engineering and there seemed always to be something new . Not too many worries about health and safety in those days either ! Thanks again , MichaelW
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Post by Deleted on Apr 26, 2015 11:47:25 GMT
The power given out by some of these transmitter stations is considerable .
I made several crystal sets with varying success . Never got far with coal or razor blades and whisker - they did work but not much signal got through and they were very noisy .
Real success came with the arrival of small signal diodes at pocket money prices . On a winters night and with a good arial and earth connection the Home Service could be received loud and clear . Often got fragments of many other stations world wide as well .
I was always intrigued by the fact that all the power needed to work the set came through the air from transmitters numerous miles away .
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Post by GWR 101 on Apr 26, 2015 12:14:18 GMT
Ah those were the days, crystal sets... lying in bed wearing a set of ex war department ear phones one could be flying a Spitfire, or driving a tank. Paul
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Post by alanstepney on Apr 26, 2015 12:32:15 GMT
It is not much different today. I made up some kits of crystal sets, and get the youngsters to assemple them and watch the thrill on their faces when they get the local station on an earpiece without any batteries, and, more importantly, that they have made themselves.
That interest might just lead to them getting a career in electronics, and perhaps they will be the ones who help preserve things in x years time.
Meanwhile, for those who are solely interested in model engineering, I will just say that there is a large overlap between those who make models and those interested in radio / electronics. Some 25% or more, have both hobbies, robably due to a basic interest in making things.
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Post by steamlaser on Apr 26, 2015 17:15:08 GMT
It is not much different today. I made up some kits of crystal sets, and get the youngsters to assemple them and watch the thrill on their faces when they get the local station on an earpiece without any batteries, and, more importantly, that they have made themselves. That interest might just lead to them getting a career in electronics, and perhaps they will be the ones who help preserve things in x years time. Meanwhile, for those who are solely interested in model engineering, I will just say that there is a large overlap between those who make models and those interested in radio / electronics. Some 25% or more, have both hobbies, robably due to a basic interest in making things. When building amateur radio gear there is often metal bashing and fixing of bits inside cases. When you get into microwaves, you then start to need to build components to very tight tolerances from interesting materials. For example ,building microwave filters requires, turning, milling and silver soldering skills. It is interesting the number of Radio Amateurs who are members of my ME club.
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Post by chris vine on Apr 27, 2015 19:51:49 GMT
I made a crystal set when I was at school.
I had a variable capacitor/trimmer which had its capacity range on it, so with a calculator I worked out the number of turns I would need, on my scrap piece of ferrite rod, to tune it to roughly 1500 metres, Long Wave.
Imagine my delight (and surprise) when I connected it to a long aerial and earth, to find that is was perfectly tuned to Radio 4, before I even adjusted it!!!
Alan Stepney will certainly call that beginners luck!!!!
Chris.
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Post by andyhigham on Apr 27, 2015 20:16:51 GMT
The hardest part about a crystal set is the aerial
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Post by chris vine on Apr 27, 2015 21:40:35 GMT
For me the Aerial was the iron framed of my school bed and the earth was the heating pipe (never hot!) just behind..
Chris.
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Post by Deleted on Apr 27, 2015 22:06:36 GMT
There were always claims that a good length of wet string would work as an aerial on long wave . Never actually tried that but did get good results with a washing line .
Long before even crystal sets there were designs published for valveless Morse receivers based on a 'Coherer ' .
Apparently a phial of fine particles would react to strong radio signals by the particles clinging together . Tap the phial and they loosen again . The difference in conductivity and resultant current flow from a battery was sufficient to set/unset a sensitive relay .
Needed a mechanical device to tap particles loose after each detect .
Not sure what the material of the particles was but probably something like iron filings or an iron filings/carbon granules mix ?
System seems to have actually worked and was even used for primitive radio control .
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Post by alanstepney on Apr 28, 2015 6:40:46 GMT
Wet string does make an aerial, and the iron frame / springs of a bed is traditional. Both work quite well.
The coherer was the standard detector in the early days, filled with iron filings, that stick together on receipt of a signal, they need a de-coherer to "unstick them" ready for the next signal. (The de-coherer was basically the mechanism from a bell.)
It was only when Jagadir Chandra Bose (no relation to the Bose of todays audio fame.) took some coherers back to India and found that the humidity caused them to stick together made him seek alternatives. Which he did, the crystal detector. They can be mnade from many materials (I have several in my collection), but one of the best was lead sulphide, (Galena) which formed the basis of most "cats-whiskers", which many of us used.
other materials were used later, including carborundum, iron oxide (often razor blades) etc.
John Ambrose Fleming (who named the valve and researched it) made the thermionic detector, but the Patent meant that royalties had to be paid,whereas Bose refused to benefit from his invention and so the crystal was cheaper, hence its popularity.
All these can be read about in early Model Engineer magazines, which make interesting reading.
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