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#1
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Looks like a power chassis, but I know squat about these forgotten stepchildren of early color.
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Evolution... |
#2
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rcafan, the 15" Westinghouse color set has a separate power supply chassis for B+ and filaments down below. How can you sen not have one? How about a photo of your chassis? I am very curious.
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John Folsom |
#3
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It was senior moment John! It's there.
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#4
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There was no ACC signal being broadcast in 1954-56. None of the early color sets had and automatic color correcting. They all used a color oscillator phase locked to the burst. Some designs had a crystal in the loop, others (like Westinghouse and Sparton) did not. The Westy used R-Y/B-Y demodulation as opposed to I/Q demodulation.
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John Folsom |
#5
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The ACC circuit in the 4 was used to control the gain of the bandpass amp, and depended on the strength of the burst signal. I've wondered if RCA issued a mod to bypass the ACC, allowing for manual-only control of the gain. There isn't any such mod in the lit I have on the 4, and my chassis has all the other mods.
Kevin
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stromberg6 |
Audiokarma |
#6
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Gotta luv sitting in on this deep engineering arcana that the average tube jockey was never privy to 'back in the day'.
oc |
#7
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Quote:
I'm happy just to have a few hours a week to devote to vintage video and radio. If I ever retire, ha-ha, I have a bleep-load of projects just waiting to be attempted. Kevin
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stromberg6 |
#8
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Yeah, at the risk of sounding sacreligious, its kinda like lookin' over the Good Lord's shoulder & reading His "Crib Notes" when He made the World...
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Benevolent Despot |
#9
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I and Q demodulation will give you the same color rendition as an R-Y /B-Y system if the gains and phases are set properly. You can't get the wide I channel but that is really hard to see. |
#10
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Quote:
The irony, now that analog TV is on its way out, is that RY demod was used because it's easier and cheaper in the analog domain, and one could "play around" with the angles to "improve" flesh tones to compensate for picture tube colorimetry; you can't "play around" with IQ demod. But now digital methods make IQ demod easy, and a digital matrix can make any required adjustmant to vectors. Part of the fascination of early colour sets is that the design did everything the hard way. Last edited by MelodyMaster; 06-25-2011 at 12:19 PM. |
Audiokarma |
#11
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Block diagram of H-840CK15
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#12
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It is a linear system and you can make the same hues with either system. The design goals were different and that it why the look different. The bandwidth doesn't affect the hue. A 90 degree (R-Y)/(B-Y) system produces the same hues as a 90 degree I/Q system.
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#13
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Quote:
And, subjectively, again, oranges and thus flesh tones just look richer, backgounds have more saturated colour, whether or not there is a technical basis for that observation. Actually, having accurately rendered green and cyan dark areas is something that very few sets get right, maybe due to chroma-luma gamma tracking, which again seems better with full bandpass demodulation. (and the "I" channel is orange and cyan..) As for background colours, my Samsung plasma TV (PN50C8000) gets it right - as does the Ikegami, I tried a Sony LCD which was way off for background colours, as was my Sony XBR. (but the Sony HX800 was marginally more accurate on flesh tones, even after calibration of the Samsung) The Conrac is better than either Sony set but worse than the Ikegami. Last edited by MelodyMaster; 06-26-2011 at 12:21 PM. |
#14
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Agreed
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#15
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Ah, good! :-)
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John Folsom |
Audiokarma |
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