I just learned that the transformer used in the schematic I posted
"is a small bell transformer with a 230v primary and an 8 – 10 v secondary. Fitted 'wrong way around' it serves admirably as a step-up transformer. For North American applications you would need a 115v primary with a 4-5 v secondary, again installed the wrong way round.
Given the way the transformer is being used in the circuit, either type of transformer should work in any part of the world. It will just be easier to find the 230V one in Europe and the 115V one in North America, since they are more commonly used there.
The principle is quite simple but effective, when larger DC current flows through the secondary winding it saturates the transformer to overwhelm the low current but high frequency AC."
So any suggestions as to an exact part number or source will be greatly appreciated!
Given the above description, this one should work: Triad Magnetics F8X
Mouser has several other similar transformers listed in their catalog, but the F8X was the cheapest one currently in stock. If you're willing to wait a bit you could go with the F7X
instead and save a few bucks (it is currently out of stock with a 4 week lead time).
Edit: I am somewhat concerned about the current carrying capabilities of the secondary. If the circuit is used the same way as notfred's, then it needs to be able to pass the entire DC motor current through the secondary (i.e. what would've been the primary if it was wired the right way around). Might actually need to upgrade to a transformer with higher current capabilities to avoid overheating the windings. Given this, I would not use the F7X... get the F8X at least. Maybe notfred can comment.