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two screenshots from 'Call the Midwife'
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two screenshots from 'Call the Midwife'
"Bill Wright" wrote in message ... https://dl.dropboxusercontent.com/u/...311_235524.jpg https://dl.dropboxusercontent.com/u/...311_235608.jpg Bill Ah yes, I remember Test Card C; but was there a Test Card A and B too? Y. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com --- news://freenews.netfront.net/ - complaints: --- |
two screenshots from 'Call the Midwife'
Bill Wright wrote:
https://dl.dropboxusercontent.com/u/...311_235524.jpg https://dl.dropboxusercontent.com/u/...311_235608.jpg Being the BBC, I'd guess that they were able to lay their hands on an 405-line test-card monoscope. If they'd wanted to display video, it seems that there's an American company, Aurora Design, that make TV standards converters, including a PAL625 to 405 line with System A modulator: http://www.tech-retro.com/Aurora_Des...Converter.html |
two screenshots from 'Call the Midwife'
"Dave Farrance" wrote in message
... Bill Wright wrote: https://dl.dropboxusercontent.com/u/...311_235524.jpg https://dl.dropboxusercontent.com/u/...311_235608.jpg Being the BBC, I'd guess that they were able to lay their hands on an 405-line test-card monoscope. If they'd wanted to display video, it seems that there's an American company, Aurora Design, that make TV standards converters, including a PAL625 to 405 line with System A modulator: http://www.tech-retro.com/Aurora_Des...Converter.html It's hard to remember back to the days when TV screens had such rounded corners. In the 1970s I had an old 405-line TV (my grandpa gave it to me when he bought a colour TV) which was probably late 1950s vintage, and that had a screen that was more or less rectangular with a bit of rounding on the corners - nowhere near as as oval as the one in Bill's photos. Ah, the joys of "vertical hold", "horizontal hold", "frame linearity" and "spot wobble" controls on the back of a TV - and that smell of hot dust. I wonder how long it took the capacitors in the EHT to discharge after the set was switched off. I opened my set to take a tapping off the speaker to a headphone socket by my bed (so I could watch in bed without mum and dad knowing!) and I left the set unplugged for a day and then took great care to avoid the leads that went to the screen and the associated EHT components, but I wonder if I was still taking a risk... |
two screenshots from 'Call the Midwife'
"NY" wrote in message
o.uk... "Dave Farrance" wrote in message ... Bill Wright wrote: https://dl.dropboxusercontent.com/u/...311_235524.jpg https://dl.dropboxusercontent.com/u/...311_235608.jpg Being the BBC, I'd guess that they were able to lay their hands on an 405-line test-card monoscope. If they'd wanted to display video, it seems that there's an American company, Aurora Design, that make TV standards converters, including a PAL625 to 405 line with System A modulator: http://www.tech-retro.com/Aurora_Des...Converter.html It's hard to remember back to the days when TV screens had such rounded corners. In the 1970s I had an old 405-line TV (my grandpa gave it to me when he bought a colour TV) which was probably late 1950s vintage, and that had a screen that was more or less rectangular with a bit of rounding on the corners - nowhere near as as oval as the one in Bill's photos. Ah, the joys of "vertical hold", "horizontal hold", "frame linearity" and "spot wobble" controls on the back of a TV - and that smell of hot dust. I wonder how long it took the capacitors in the EHT to discharge after the set was switched off. I opened my set to take a tapping off the speaker to a headphone socket by my bed (so I could watch in bed without mum and dad knowing!) and I left the set unplugged for a day and then took great care to avoid the leads that went to the screen and the associated EHT components, but I wonder if I was still taking a risk... The tubes themselves with a capacity of around 500pF could hold a good charge. |
two screenshots from 'Call the Midwife'
"Phi" wrote in message
... "NY" wrote in message I wonder how long it took the capacitors in the EHT to discharge after the set was switched off. I opened my set to take a tapping off the speaker to a headphone socket by my bed (so I could watch in bed without mum and dad knowing!) and I left the set unplugged for a day and then took great care to avoid the leads that went to the screen and the associated EHT components, but I wonder if I was still taking a risk... The tubes themselves with a capacity of around 500pF could hold a good charge. But were there safety resistors to discharge the HT PSU capacitors and the tube's capacitance reasonably quickly once the power was removed? |
two screenshots from 'Call the Midwife'
On 12/03/2015 09:24, Y Dangle wrote:
Ah yes, I remember Test Card C; but was there a Test Card A and B too? Yup! See http://www.testcardcircle.org.uk/tchistory.html Richard |
two screenshots from 'Call the Midwife'
On Thu, 12 Mar 2015 03:28:30 +0000, Bill Wright
wrote: https://dl.dropboxusercontent.com/u/...311_235524.jpg https://dl.dropboxusercontent.com/u/...311_235608.jpg Bill Is that the right card for the period though? The one I remember had "BBC" in black with the second B inside the white C, making me wonder what bCbc stood for! So the question for me is, was this generic testcard C regularly transmitted at the time depicted in the programme? Nicely done though. If that set contains its original chassis I trust there was someone with a CO2 fire extinguisher just out of shot. -- Graham. %Profound_observation% |
two screenshots from 'Call the Midwife'
On Thu, 12 Mar 2015 14:40:17 -0000, "NY" wrote:
"Phi" wrote in message ... "NY" wrote in message I wonder how long it took the capacitors in the EHT to discharge after the set was switched off. I opened my set to take a tapping off the speaker to a headphone socket by my bed (so I could watch in bed without mum and dad knowing!) and I left the set unplugged for a day and then took great care to avoid the leads that went to the screen and the associated EHT components, but I wonder if I was still taking a risk... The tubes themselves with a capacity of around 500pF could hold a good charge. But were there safety resistors to discharge the HT PSU capacitors and the tube's capacitance reasonably quickly once the power was removed? The picture tube _was_ the EHT capacitor. With something like 12 to 15KV (or thereabouts), just how many high voltage 10M ohm resistors do you reckon would have been needed to be strung together to avoid excess leakage and arc over? In practice none because it was a needless expense to deal with a problem only a properly trained and equipped TV repairman would be allowed to deal with in the first place. -- J B Good |
two screenshots from 'Call the Midwife'
On Thu, 12 Mar 2015 16:32:36 +0000, Johny B Good
wrote: I wonder how long it took the capacitors in the EHT to discharge after the set was switched off. I opened my set to take a tapping off the speaker to a headphone socket by my bed (so I could watch in bed without mum and dad knowing!) and I left the set unplugged for a day and then took great care to avoid the leads that went to the screen and the associated EHT components, but I wonder if I was still taking a risk... The tubes themselves with a capacity of around 500pF could hold a good charge. But were there safety resistors to discharge the HT PSU capacitors and the tube's capacitance reasonably quickly once the power was removed? The picture tube _was_ the EHT capacitor. With something like 12 to 15KV (or thereabouts), just how many high voltage 10M ohm resistors do you reckon would have been needed to be strung together to avoid excess leakage and arc over? In practice none because it was a needless expense to deal with a problem only a properly trained and equipped TV repairman would be allowed to deal with in the first place. I used to find that a screwdriver worked extremely well. Earth it to the chassis with a short piece of wire with croc clips, and then slip the blade of it under the EHT connector cap on the tube. Rod. |
two screenshots from 'Call the Midwife'
"Dickie mint" wrote in message ... On 12/03/2015 09:24, Y Dangle wrote: Ah yes, I remember Test Card C; but was there a Test Card A and B too? Yup! See http://www.testcardcircle.org.uk/tchistory.html Richard Cheers Richard --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com --- news://freenews.netfront.net/ - complaints: --- |
two screenshots from 'Call the Midwife'
On 12/03/2015 16:02, Graham. wrote:
So the question for me is, was this generic testcard C regularly transmitted at the time depicted in the programme? Further reading http://www.pembers.freeserve.co.uk/Test-Cards/index.html#405-Lines -- Mark Please replace invalid and invalid with gmx and net to reply. |
two screenshots from 'Call the Midwife'
On 12/03/2015 14:40, NY wrote:
But were there safety resistors to discharge the HT PSU capacitors and the tube's capacitance reasonably quickly once the power was removed? I remember working on some CRT based test equipment of that era. A common fault was an open circuit discharge resistor! -- mailto: news {at} admac {dot] myzen {dot} co {dot} uk |
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