When did synchronization to the mains end?

[ukcol]

In the early days of 405 TV the transmitted signal was synchronized to the mains supply. This allowed the smoothing circuits of the receivers to be less than perfect so that any hum on the picture would be stationary and therefore less noticeable.

Was this practice continued all the way up to the start of colour TV or did it finish earlier?

[Nuvistor]

I seem to remember BBC2 was not synchronised from the start, so that would be 1964. I don't know if the 405 transmitters carried on with the sync though.
One problem with syncing to the mains is when BBC were on one half and ITV were on the other half wave, if the smoothing was poor the picture would change shape on channel change.
Frank

[FERNSEH]

I remember when BBC1 on 405 lines ceased to be synchronised to the 50Hz mains, this was sometime in 1964. Prior to the changeover to unsynchronised syncs many sets with inefficient HT smoothing appeared to work OK, after the changeover to the asynchronous timebases the pictures on these sets could be seen as having a "breathing" effect.
New HT smoothing capacitors had to be fitted to solve the problem.
Bush made a version of the TV22 designed for a unsynchronised mains supply.
Model TV22U?

DFWB.

[Nuvistor]

I wonder if the BBC1 in 1964 ceasing syncing was due to doing the same with BBC2?
Frank

[KeithsTV]

And probably part of the preparation for colour where everything is synced to the colour subcarrier.

keith

[FERNSEH]

Originally Posted by Nuvistor

I wonder if the BBC1 in 1964 ceasing syncing was due to doing the same with BBC2?

Hi Frank,
I reckon that exactly what happened, no doubt they would be testing the all new 625 to 405 standards converters and as the input standard is asynchronous it would make sense to de-synchronise any other signals generated from a 405 line source in the same manner.

DFWB.

[ukcol]

Thanks for the replies gents that helps a lot. I realized that the practice had gone by the time colour came along but not the detail. I also realized that it could not be done for colour TV because of the special relationship between the colour sub-carrier and the line sync. It probably would have been easier to synchronize the national grid to the sub-carrier rather than the other way round.

[Andrew2]

I certainly remember what we called 'flag-waving', a slow waving effect on the picture caused by poor HT smoothing. I entered the trade in 1969, so the non-synchronous step had obviously been taken by then.
As others have said, it was probably in the early 60's to make way for colour.

[Karen O]

I read somewhere that studio lighting was part of the motivation for synchronisation to the mains. Is that a myth or did they find a way around the problem, whatever the problem was?

[Peter.N.]

I remember in the '50s some very fast waving and low mains voltages, down to 180v at times in the evening, by which time most sets had stopped working, the frequency regulation must have been dreadful.

Peter

[red16v]

Originally Posted by Karen O

I read somewhere that studio lighting was part of the motivation for synchronisation to the mains.

I don't quite see why, most studio lighting of the era would have been based on incandescent lamps, give the amount of thermal inertia they have I can't readily see an issue.

Even though today's studios are trying to move over to LED/fluorescent lighting, incandescent lamps are still widely used in all the big studios I know of.

[G8HQP Dave]

Originally Posted by ukcol

It probably would have been easier to synchronize the national grid to the sub-carrier rather than the other way round.

Both ways round would create significant problems. In addition, except under severe fault conditions, there is just one national grid frequency for Great Britain so whose colour subcarrier should be chosen for synchronisation?

[broadgage]

I agree that the TV studio lighting would have been a non-concern for the reason already given of thermal inertia in the lamp filaments.

Lamps for TV studios were among the highest wattage incandescent lamps made, 5KW was a common size and some were 10KW.
Line frequency flicker is almost undetectable in such large filament lamps.

Discharge lamps or AC carbon arcs would flicker at twice line frequency and therefore found very little favour for TV studios.

As has already been said, todays TV broadcasts are not synchronised to the grid frequency. This may be observed when mains frequency fluorescent lighting can be seen in the background of outside news broadcasts.
An interview in the street might be conducted mainly by daylight, perhaps supplemented by battery powered lights.
Fluorescent lighting in windows can then seem to flicker noticeably.

[emeritus]

The Focal Encyclopaedia of Photography has a passing reference to the fact that the flicker of fluorescent tubes can be overcome by using them in groups of three, each connected across different pairs of phases of a three-phase supply. I can't say that flicker has been apparent in my camcorder footage shot under fluorescent lighting, but then I always selected 1/50 second shutter speed to get smooth motion. Modern video camera practice seems to be to use very short shutter speeds, possibly to avoid diffraction that would accompany the use of a small aperture in bright light. A short exposure time does allow sharp stills to be obtained, but results in juddery motion due to the absence of significant integration during the exposure of each frame.

It was mentioned in a thread on this forum some time ago that the persistence of the original tubed video cameras could be utilised in standards conversion of NTSC to PAL and vice versa, by simply pointing a camera at a high quality studio monitor. So I guess that mains flicker would have been unlikely to have been a problem in the early days of TV. My personal experience some years ago was that an elderly Panasonic VHS-C camcorder could be used to capture 8mm cine without needing to accurately adjust the projector speed, unlike more recent DV camcorders, where the projector needs to be adjusted to precisely 16 2/3 frames per second to eliminate flicker with a shutter speed of 1/50 sec.

[Craig Sawyers]

Theatres still almost all use incandescent lighting with gels in front, like what seems for ever. Rock concerts have almost entirely moved across to LED - but they are not lit subtly, mainly primary colours, and use fast colour change effects.

[Jac]

Originally Posted by Karen O

I read somewhere that studio lighting was part of the motivation for synchronisation to the mains. Is that a myth or did they find a way around the problem, whatever the problem was?

The lighting certainly also contributed to problems.
To overcome this, in the late '40's Philips used water cooled mercury studio lighting.
It consisted of groups of 3 lamps, mounted very close together, each on a different phase of a 3-phase supply.
This way the 100 Hz flicker when using one lamp, was reduced to negligable proportions.

Sometimes studios used DC for the lamps, to avoid the flicker.

Jac

[peter_scott]

Originally Posted by emeritus

unlike more recent DV camcorders, where the projector needs to be adjusted to precisely 16 2/3 frames per second to eliminate flicker with a shutter speed of 1/50 sec.

I think you are better using slow shutter speeds rather than trying to match frame rates asynchronously. Using 1/50 sec you will generate aliasing effects. In most of my YouTube videos of television screens I use a slow shutter speed to avoid black bars. Admittedly it does compromise fast moving sequences but it's less noticeable than the bars.

e.g.https://www.youtube.com/watch?v=e7Q0wGfeMPo

Peter

[emeritus]

I was able to modify an old UPS power supply kindly donated by a forum member to provide a variable frequency 240V AC supply by fitting an external 10-turn pot to adjust the frequency precisely. At anything other than precise synchronisation, there is noticeable brightness modulation. The 10-turn pot allows precise frequency adjustment and flicker-free video. I could not find any information about the range of shutter speeds that are possible (or indeed if any adjustment is possible) with the current generation of consumer camcorders. 1/50 sec is the slowest shutter speed I have come across.

When we were in France for the Eclipse (my late brother-in-law's house lay on the line of maximum totality, and the clouds dispersed just in time), I was able to record bar-free video of the TV coverage on his French (SECAM) TV by pointing my (JVC VHS-C) camcorder at the screen and switching it on and off until the frames became synchronised. This completely eliminated bars and torn frames, and synchronism was maintained for the time the camcorder remained switched on.

[Heatercathodeshort]

Originally Posted by FERNSEH

The pictures on these sets could be seen as having a "breathing" effect.
New HT smoothing capacitors had to be fitted to solve the problem.DFWB.

Yes David it was 1964. I was 16 at the time and remember replacing large numbers of smoothing blocks in the RGD/Regentone Ten4/12/17-18 etc. The picture breathed like a Leach !It seemed to effect this series of models more than others. John.

[Vintage Engr]

Originally Posted by ukcol

Was this practice continued all the way up to the start of colour TV or did it finish earlier?

It did finish earlier, although I can't recall the exact timing.
Before I moved into the Broadcast Industry, I worked for Rediffusion, the rental arm of the company. We had some very ingenious engineers working at our branch, and it was not unknown for them to 'modify' some T.V's when all else failed to fix a fault.
Some 405-line sets with flywheel sync that didn't lock very well, ended up with a tobacco tin, and an extra ECC82, converting back to 'straight sync'. The more unscrupulous guys would often hard-wire the frame sync to the mains, taking a feed at the low end of the heater chain! It did work, after a fashion.
What I do remember, is a whole group of customer calling to say that they had frame-roll, - this was when the transmissions ceased to be locked to the mains. There were a few red faces, as these customers were mainly on the area covered by said 'engineer'.

I'd forgotten about all this until you raised the subject.

Dave.