What is the pinout of this transformer?
Very low resistance measurements are &quot;normal&quot; for transformers.   All you're measuring is the DC resistance of a long piece of copper wire.  You're not measuring &quot;anything&quot; about the transformer itself.
Specifically, resistance won't tell you the turns ratio (which is what you need to know to boost or cut output voltage).   You need to use an AC source and measure (preferably with an oscilloscope) the output.  This is nowhere near as easy or as straightforward as you're hoping.  You might consider just buying a properly spec'd transformer where you &quot;know&quot; what's inside.  They're not really all that expensive.
https://forum.allaboutcircuits.com/threads/assessing-an-unknown-transformer.38273/
*edit, see you just added a link to the same transformer on EBAY.  That's an audio amplifier transformer.  It may very well not have any high-voltage outputs (unless maybe one pair of wires is intended for a vacuum fluorescent display).   I don't know anything about that Sony receiver, maybe you can find a schematic and it'll give you some clues....