Help on derailer oddball?

[stump]

I can't find any info on the following derailer, it's an older Shimano sis rd ty20 is what is stamped on it. I can only find the L and H screws no B adjustment. It's on a converted mtb I'm using as a triathlon trainer till my $$$$ are ready for a tri bike. I like the extra weight it has to help build up some endurance for when I go to my tri bike. It is an older Schwinn model

[TESTUser111]

It's about the least expensive derailleur you can get, which is why there is no B adjustment screw.

[stump]

Thanks, now I know I'm not crazy.