They don't say that Thomas, they are marked as acetylene then they say pressurized gas regulator. They are both older made in the USA regulators.
I messed with it some more this evening and I think it is in the valve. When I open the valve on the 100 lb. with nothing hooked to it I can hear a good volume of gas coming out but not much pressure. When I do the same with the 20 lb. tank I hear a lot more coming out and it is down to about a 1/4 tank. So it seems there isn't enough pressure coming out of the 100 lb. to work through the regulator. I tapped on the valve and didn't notice any difference, with the valve closed I sprayed some brake clean in, blew that out with compressed air then I filled it with penetrating oil and put a silicone plug in it. I will let that sit overnight and see if it helps. I got to thinking and this tank has sat for some long periods of time so maybe something is seized up.
It has about 40 or 50 pounds of propane in it so I don't know what to do about that if I want to change the valve, I guess I would just take it down by the woods on a breezy day and crack open the valve.
I looked at some adjustable propane regulators on Ebay and I might try one but the setup I have now has better gages and a nice long hose that I hate to give up.