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Originally Posted by NewVista
Very intriguing as the BBC had unlimited spending & clout....
So why did EMI use 4 (identical?) tubes ? Apparently the thinking in the sixties was that having a separate Y channel would mask registration drift - a problem later solved enabling 3-tube (Model 2005) with stable scan (Op-Amps, Neg feedback...)
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The BBC certainly didn't have plenty of money.
Why 4 tubes? 2 main reasons. One is registration, as mentioned above. The other is more subtle relating to gamma and constant luminance. The late Ivan James of EMI was a great proponent of constant luminance and may well have influenced the design. Here's Poynton's view on the subject:
http://www.poynton.com/notes/video/C...luminance.html
Later designs used "highs out of green" and suchlike, recognising that green is a reasonable proxy for luminance.
06-25-2010, 01:22 AM
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