The ISO NP-126 has 2 primary windings and can be used
as SE to SE, or PP to SE, or SE to PP.
the 2 primary windings connected in series the NP-126
can be used with tubes which internal resistance is
between 10K and 20K. (tubes with lower internal resistance
are always possible) When the primary windings are
connected in parallel the NP-126 can be used with
tubes which internal resistance is between 2K5 and
The NP-126 can also be used reversed. In that case
it acts as an input transformer.