tv sync
Nigel you are quite correct 405 line service was am video and sound when i wrote that post i should have read it before submission but alas somewhere owing to the late hour and nostalgia i got my modulations mixed up with sat systems , i have since reread it and i didnt claim that broadcasters didnt transmit sync signals of course they do but in the early days they used the mains as a timebase , tv recievers also used the mains as a time base to provide tube deflection until a station was recieved and to provide deflection should the station go of air , this was to avoid a nasty burn in on the tube face , some of the early sets where manufactured more like a cottage industry some where even built as kits from old decca and marconi ww2 surplus radar sets , another reason for using mains sync on these old sets was that unlike today where the flyback current from the yoke produces the e.h.t via a line output transformer e.h.t was produced either by stepping up the mains or some other form of inductive increase so in the absense of any sync signals eht was still present and a threat to the tube unlike todays sets where the absense of either vertical or horizontal sync can be protected by beam limiter circuits e.t.c . As for valve instability you are correct as well but i never in my post claimed that thermionic valves where stable devices in fact in my first workshop the most used tool on old sets wasnt a scope but an old pifco hairdryer fitted with a toggle switch to run hot or cold when fault finding valve stages ,you are also correct that i didnt state my country , back when i was a kid i lived in dublin the first national tv service (1959) was rte which transmitted 625 lines on vhf band 3 to most of the south and midlands , in the border counties where a lot of people had 405 line sets to pick up bbc from the north they had some small repeaters on 405 lines at band 1 and 3 the british later adapted 625 line for uhf only , Nigel i like to call a spade a spade and honestly when i recieved the email i found it extremly rude to say the least , among most tv fixers of my vintage the term used if you dissagreed with someone on a technical matter would be something like " i think you may be mistaken about that" or words to that effect , i see your profile says electronic god well im no god myself just an old tv guy , that post was my first post in this group i was trying to be friendly , there is no need to reply to this post as it is my last here .
P.s also i didnt say that sets werent synced of the incoming signal , the mains was used as sync in the absense of a transmission , and the very earliest sets did use the mains as sync thats why the hold control was used to lock the picture ,thats why there would be picture roll when you changed channel , i know valves could be unstable but not that badly when they where fully heated, later on sets improved with sync seperation due to a little device called a vic =vertical intergrater couplet module it looked like a ceramic capactor that had a bad case of the boils
Nigel you are quite correct 405 line service was am video and sound when i wrote that post i should have read it before submission but alas somewhere owing to the late hour and nostalgia i got my modulations mixed up with sat systems , i have since reread it and i didnt claim that broadcasters didnt transmit sync signals of course they do but in the early days they used the mains as a timebase , tv recievers also used the mains as a time base to provide tube deflection until a station was recieved and to provide deflection should the station go of air , this was to avoid a nasty burn in on the tube face , some of the early sets where manufactured more like a cottage industry some where even built as kits from old decca and marconi ww2 surplus radar sets , another reason for using mains sync on these old sets was that unlike today where the flyback current from the yoke produces the e.h.t via a line output transformer e.h.t was produced either by stepping up the mains or some other form of inductive increase so in the absense of any sync signals eht was still present and a threat to the tube unlike todays sets where the absense of either vertical or horizontal sync can be protected by beam limiter circuits e.t.c . As for valve instability you are correct as well but i never in my post claimed that thermionic valves where stable devices in fact in my first workshop the most used tool on old sets wasnt a scope but an old pifco hairdryer fitted with a toggle switch to run hot or cold when fault finding valve stages ,you are also correct that i didnt state my country , back when i was a kid i lived in dublin the first national tv service (1959) was rte which transmitted 625 lines on vhf band 3 to most of the south and midlands , in the border counties where a lot of people had 405 line sets to pick up bbc from the north they had some small repeaters on 405 lines at band 1 and 3 the british later adapted 625 line for uhf only , Nigel i like to call a spade a spade and honestly when i recieved the email i found it extremly rude to say the least , among most tv fixers of my vintage the term used if you dissagreed with someone on a technical matter would be something like " i think you may be mistaken about that" or words to that effect , i see your profile says electronic god well im no god myself just an old tv guy , that post was my first post in this group i was trying to be friendly , there is no need to reply to this post as it is my last here .
P.s also i didnt say that sets werent synced of the incoming signal , the mains was used as sync in the absense of a transmission , and the very earliest sets did use the mains as sync thats why the hold control was used to lock the picture ,thats why there would be picture roll when you changed channel , i know valves could be unstable but not that badly when they where fully heated, later on sets improved with sync seperation due to a little device called a vic =vertical intergrater couplet module it looked like a ceramic capactor that had a bad case of the boils
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