You can't feed a VCR into an RGB converter as a VCR does not output RGB. A standard VHS VCR only outputs composite video, an SVHS VCR will also output S-Video.
To feed your VCR to plasma you could (depending on what available inputs the plasma has) get a scart to composite (plus stereo audio if required) lead such as
These. Just make sure you get the correct lead as they are directional. The signal must travel from scart to phono, or get a scart with a switch so it can work in either direction.
Mark.
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