Quote:
Originally Posted by NewVista
My objections to these 'reasons', that you hear now and then, for 50hz countries using 25fps TV are as follows:
1. TV's (even old ones) shouldn't have AC power artifacts. If you see this, I suggest you book the set in for repair.
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This is not so straightforward as Jeff and the Blumlein article have pointed out. Firstly, removing ripple from the power supply to an adequate level is VERY difficult to do cost effectively using 1930/40's technology. The required amount of iron and capacitance would make the set very heavy and very expensive. The power supply on the 1936 RCA RR359 prototype sets weighs almost 100lbs by itself due to the size and number of chokes.
The problem is compounded by interlace scanning. Only a very small amount of magnetic interference is required to shift a line enough to ruin the interlace. Just having a power transformer in the set will create enough magnetic interference to show ripple in the image. Magnetically shielded transformers could be used but again are very expensive and large.
Case in point, I have a Sony 9-90UB solid state 405 line set from the 1970's and when I run it here on 60Hz power, feeding it with a 405/50i signal, the picture shows pronounced ripple and line bunching. Even when powered from a battery to eliminate the internal transformer, there is still some noticeable ripple in the image depending on where the set is placed due to stray magnetic fields at 60Hz.
Edit: I see Steve got in there while I was typing
This is why the power supply on the RR359 is so big and heavy. They have large chokes and capacitors in the mains derived EHT to try to filter out the ripple. Hardly something that would be practical on a commercial set.