The ben heck mod doesn't seem to work well on my Commodore monitor (third party monitor), yet on my HDTV works fine... On other SDTV's, the picture is stable, but totally dark and washed out...
http://blackevilweredragon.spymac.com/atarimod1.jpg (http://blackevilweredragon.spymac.com/atarimod1.jpg)
http://blackevilweredragon.spymac.com/atarimod2.jpg (http://blackevilweredragon.spymac.com/atarimod2.jpg)
(The HDTV. notice it's a perfect picture) http://blackevilweredragon.spymac.com/ataricomposite1.jpg (http://blackevilweredragon.spymac.com/ataricomposite1.jpg)
(The commodore monitor.. notice it's horizantle hold is very weak for some reason) http://blackevilweredragon.spymac.com/ataricomposite2.jpg (http://blackevilweredragon.spymac.com/ataricomposite2.jpg)
Incase it matters, here's the back of the Commodore third party monitor: http://blackevilweredragon.spymac.com/cmonitor.jpg (http://blackevilweredragon.spymac.com/cmonitor.jpg)
That type of passive mod produces a relatively weak signal that some monitors simply won't lock onto.
This site: http://www.cheeptech.com/2600mods/2600mods.shtml (http://www.cheeptech.com/2600mods/2600mods.shtml) is a comparison of the various 2600 video mods. He also mentiones that running the output from the modded 2600 through a VCR can stabilise it.
I had planned to do the CD4050 mod on one of my 2600s, but I still haven't gotten around to it. I don't play enough 2600 to really justify the effort, but that doesn't mean I won't do it eventually for.
I spent a bit of time on this a few years ago. I pulled apart a few different models of atari 2600 with the aim of creating some good docs on getting composite video out from the thing. It is possible to get very good quality composite video from an atari (not the typical 'only works of some tvs' and 'colours all wrong' type shit that most mods leave you with) good enough that there is no significant difference between composite and s-video (due to the primitive, low res graphics).
Unfortunately there are just too many different models out there - many dozens of them, making a moron's guide impossible. The video amp itself is simple, just a couple of components. But to put in place the audio mixing osc must be disables and the video load (RF modulator) removed. Which is (from the reaction I got at the time) just too hard for typical Mr. Joe Atarimodder.
So you end up with the 'CD4050 mod' which basicaly replaces a large chunk of the video circuitry which is already in place on the board... needless effort. The circuit in the atari faq needs to be modified to work on a PAL system too.
I did write up some hasty instructions for this a while ago, maybe it can be found with a search. Nobody was really interested so I didn't elaborate too much. I can't blame them really, there arn't too many games on the old atari worth taking the time to play though I really like the homebrew - Thomas Jentzsch's Thrust.