  Aims: Hydrogen and helium line spectra are crucial diagnostic features for
the quantitative analysis of OB stars. We compute synthetic spectra based on a
hybrid non-LTE approach in order to test the ability of these models to
reproduce high-resolution and high-S/N spectra of dwarf and giant stars and
also to compare them with published grids of non-LTE (OSTAR2002) and LTE
(Padova) models. Methods: Our approach solves the restricted non-LTE problem
based on classical line-blanketed LTE model atmospheres. State-of-the-art model
atoms and line-broadening theories are employed to model the H and He I/II
spectra over the entire optical range and in the near-IR. Results: The
synthetic spectra match almost all measurable hydrogen and helium lines
observed in six test stars over a wide spectral range from the Balmer limit to
the NIR, except for only a few well-understood cases. Our approach reproduces
other published non-LTE calculations, however avoids inconsistencies with the
modelling of the He I singlets recently discussed in the literature. It
improves on the published LTE models in many aspects: non-LTE strengthening and
the use of improved line-broadening data result in overall significant
differences in the line profiles and equivalent widths of the Balmer and helium
lines. Where possible, systematic effects on the stellar parameter
determination are quantified, e.g. gravities derived from the Hgamma wings may
be overestimated by up to ~0.2 dex at our upper temperature boundary in LTE.
(abridged)
