I'd like to build a spark tx. I got to send cw on a 250 watter original HB rig from 1920 using a Thor transformer on a MARC radio club pic a nic bout 20 years ago. The owner was a ham in the spark days, he was about 81 at the time I think. His old call was just a number and 2 letters, like 3TN or something like that. he wasn't a ham anymore.
it was just a fixed gap job, but it sure sounded good. His CW was sharp as a tack. he started calling CQ on it and of course you could hear the spark from across the field... with yer ears. No RX required.
I got to call a bunch of CQ's de N3DRB on it. no antenna hooked to it, of course. had a big 4" RF Ammeter and a edgewound helix in the output.
That is where I got my love of using RF Ammeters in the open wire feeders, which I've done in every station ever since. Tune for max fire in the wire.