The present invention provides an in-line filament transformer for a vacuum device. The filament transformer comprises: a core; a primary winding and a secondary winding wound around the core, wherein the secondary winding is biased at a high voltage and the primary winding is placed in line with the secondary winding; and a shield for shielding the primary winding. In an embodiment, the transformer comprises a bobbin for incorporating primary winding and secondary winding. An arrangement of increasing creepage distance is incorporated in the bobbin by providing plurality of sections on the bobbin. The invention also provides a shield in the primary section of the bobbin for shielding the primary winding from the secondary winding. In an embodiment the shield is in the form of shield winding of thin wires wound in a defined manner.