  The evolutionary properties of the old metal-rich Galactic open cluster
NGC6791 are assessed, based on deep UB photometry and 2Mass JK data. For 4739
stars in the cluster, bolometric luminosity and effective temperature have been
derived from theoretical (U-B) and (J-K) color fitting. The derived H-R diagram
has been matched with the UVBLUE grid of synthetic stellar spectra to obtain
the integrated SED of the system, together with a full set UV (Fanelli) and
optical (Lick) narrow-band indices. The cluster appears to be a fairly good
proxy of standard elliptical galaxies, although with significantly bluer
infrared colors, a shallower 4000A Balmer break, and a lower Mg2 index. The
confirmed presence of a dozen hot stars, along their EHB evolution, leads the
cluster SED to consistently match the properties of the most active UV-upturn
galaxies, with 1.7+/-0.4% of the total bolometric luminosity emitted shortward
of 2500A.
  The cluster Helium abundance results Y=0.30 +/-0.04, while the Post-MS
implied stellar lifetime from star number counts fairly agrees with the
theoretical expectations from both the Padova and BASTI stellar tracks. A
Post-MS fuel consumption of 0.43 +/- 0.01 M_sun is found for NGC6791 stars, in
close agreement with the estimated mass of cluster He-rich white dwarfs. Such a
tight figure may lead to suspect that a fraction of the cluster stellar
population does actually not reach the minimum mass required to effectively
ignite He in the stellar core.
