Revisiting an old topic - Adding DC Restoration to a 1950s TV

[ppppenguin]

Two problems about adding DC restoration to a TV.

1: EHT regulation matters more with true black level. Change in mean brightness of the pcture may give unacceptable change in size. This sort of effect might explain your problem.

2: If the set has mean level AGC (common with +ve modulation, probably less so with -ve) then the DC restoration won't be so effective. Partly because contrast will vary with average picture level, partly because sync amplitude will vary with APL. Since a simple DC restorer stabilises sync tip, brightness will still vary with APL.