> Ideas? Thanks.

The 20% difference in frequency from 60 to 50Hz can mean 20% more core flux for
50Hz. Tightly designed small transformers cannot cope with this esp. if the
voltage is in the high range and ventilation is poor. Paralleling primaries
usually causes no problems on small transformers because the primary resistance
is relatively high, but it should be specified for this. 

Afaik for small transformers with 2 primaries in series for 220V, and one
winding body (EI shape, not O shape) only one should be used for 110V operation
(the one that shows higher R on the ohmmeter - this will be the one that is
'outside' in the winding pack and gets better cooling in air - this is
counterintuitive).

Core saturation can be 'measured' with a small speaker in series (!) with the
primary. The sound it produces becomes 'harsh' and much louder than normal when
there is saturation in the core. Notice that I put '' around 'measured'. The
impedance of a small speaker is of no consequence when used like this. Usually a
small bass speaker of 5-15W is used. This will cope well with the inrush.

The manufacturer always knows best. Unless he is not the OEM and just quotes the
datasheet he has ...

Peter


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