I have found that urn stops after outputting 4094 random numbers. I tried various values over 4094 and at slower output speeds. Has anyone else run into this problem? I am using max 5. Maybe this is different in new versions.
[urn] maxes out at 4094. End of story. It's documented somewhere, but I've been living with this so long that I can't remember where. It's been this way since about 1989.
I'm not sure if this is an issue, based on the original question, but if you need to start a new sequence when you've removed all the "balls" from the urn, trigger a 'clear' message when you get a bang out the right outlet.
Note that the difference between the behavior of [urn] and [random] becomes less and less noticeable as the size increases. By the time you get to [urn 4094], there are few situations where an observer is likely to tell the difference from [random 4094]. So maybe explain why you need such a humongous [urn]. And, of course, there are ways to build larger urns, one way following the example laonikoss provided.
Another way to get huge urns is available to folks using Litter Power with the [lp.ernie] object.