  In this paper we present the details of our previously published results for
a search for an additional neutrino mass state in $\beta$-electron spectrum
from the Troitsk nu-mass experiment. Here we present steps of the analysis,
show a set of likelihood functions obtained for each additional heavy mass
value. We demonstrate how systematic errors were estimated. We also compare our
results with those published recently for a similar analysis for Mainz data and
try to explain why there is a factor of 2-3 difference in the sensitivity for
an additional heavy mass.
