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CT-100 had 100% DC restoration. Every (or nearly every) following set had reduced DC coupling, maybe between 60% and 85%.
Excuses:
1) cheaper to partially DC couple than to restore at the video output, especially with cathode drive
2) if DC coupled, more components can get into the act and introduce large manufacturing variations
3) partial DC coupling means the set draws less beam current on mostly-light pictures, so less HV supply capacity is needed
4) broadcasts (and later, cable channels) varied greatly in DC set-up (black level), so partial DC restoration decreased these errors (provided the image was average in brightness).
Consumer's Digest complained about this for years and years, until finally the manufacturers caved in (long after tube sets were gone) and put in 100% DC restoration (or close to that), which is now the common design.
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