I got the new Micro-Matcher (as I've begun calling it...) out to the park today for some more intensive testing with an antenna up in the air with no distractions. I went to my usual spot in Bever Park and put up the PAR wire (~40') which again, is designed to work on 40, 20, and 10m. With the PAR matchbox, I had flat SWR on all bands and across the whole band. With the Micro, it was not quite the case. Luckily, in the CW portions of the bands, SWR was spot on. However, in the voice portion, that was not the case. It seems the small (dinky!) toroid was making the match much higher Q, and thus much lower bandwidth. This is no surprise, but it isn't all that bad. With the PAR wire being in tune in the CW portions of 40 and 20, it will still serve its purpose as a super tiny matcher for use with my MTR. When my new wire gets here, I'm going to replace the heavier wire used on the PAR with the lightweight 26 gauge poly-stealth, and it should work just fine.
I also tried a 66 foot wire with both matchers. The 66 foot wire is a half wave on 40m which means its a full wave on 20, 1.5 halves on 15m, and 2 full waves on 10m, all high impedance feedpoints when fed at the end, so it should work with both matchers. Unsurprisingly, the PAR matched on all 4 bands without any trouble. Very cool to pick up 15! Unfortunately, the Micro simply did not have the guts to get decent matches (<2:1) on any band. I may have been able to trim to get a better match but I trimmed it to a perfect match with the PAR and I didn't want to lose that.
So, we've learned some lessons: the FT37-43 cores are too small for a wideband transformer like the PAR. They DO work for a limited bandwidth match though. If you have the parts in your junk box, build away I say! I wouldn't go mass producing these by any means but I did make contacts on 20 and 40 with mine so it isn't snake oil. I might make one with a bigger core just to see if it matches as well as the PAR (no reason it wouldn't).
Have fun experimenting, but don't come crying to me when it doesn't work! :P Good luck at Field Day this weekend, hope to hear you all on the air. 73!