two screenshots from 'Call the Midwife'

https://dl.dropboxusercontent.com/u/...311_235524.jpg

https://dl.dropboxusercontent.com/u/...311_235608.jpg

Bill

"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.



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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

"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...

"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.

"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?

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

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%

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

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.