Buiklding a QRO 4:1 un-un with an unusual core

In Winter holidays, a friend ask me for a longwire balun and I've no toroid core available, then I look into my junkbox and I've found an old  TV EAT Transformer, like this:

I've read somewhere in the 'net that some hams use this core for building baluns and ununs, and I decidde to satisfy my friend's request using this core.

I'm inspired on the work of another italian ham radio operator, IK1ICD (you may look at his job HERE )

I arrange quickly a 4:1 un-un using the usual schematic:

I use 2x1 mm speaker wire, 2 and a half turn + 2 and a half turn + 2 and a half turn (...whew! simpler to look the picture below than describe it!)

The un-un closed in the box, ready to operate!

Another view: