[Elecraft] Max power for JT9 with K3S 100?

[Frank O'Donnell]

I've been using JT9 mode on 630m this winter with my K3S outputting to 
an external class D amp.

Now I'm interested in trying some JT9 QSOs with some people currently 
operating on 160m. For me this would mean outputting directly from the 
K3S (with internal tuner) to the antenna.

Given the 1-minute cycle time for JT9, are there recommendations 
(official from Elecraft, or otherwise) on maximum power to use in a 
situation like this? And/or, is the answer dependent on the SWR I can 
achieve with the antenna?

Thanks and 73,

Frank K6FOD