Dave
It depends upon the strength of the solution you use. If you use a
saturated solution exposures for the ammonium should, in theory, be about
one third of those for the potassium. I went over to Gloy at the same time
as I adopted the ammonium salt and I changed my technique completely so
that I now use about the same exposures for the two but use mechanical
development as the 'gum' seems to be able to stand up to it. The result is
far more cointrol over the final print which is what gum is about anyway.
Terry