Per Kevin Mayes comments in 140130 Digest:  Yes, Kevin, the best
sounds that my original Wurlitzer organ ever made (and the best it
ever played) was on summer nights, after dark, in the country.

Humidity is a major factor, on older organs especially, and is most
noticeable when playing out of doors at a rally.  The vacuum pumps
on Wurlitzer's smaller organs were also quite inadequate for all but
the best sealed organs, in my opinion.

Just my $.02

Dave Haibach - In Them Thar Hills Of Kentucky