I put up some pictures of the transformer assembly innards. The planned tight winding and mounting of a fairly big toroid worked out nicely. I found in the junk dept a brass gear piece that could be used as the bushing with minor alteration. I really wanted a flange, but couldn't find the right sort of piece. I drilled out the gear to 3/4" so that the post could go through and be firmly held inside by the right layer thickness of fish paper.
"Parts 1" shows the basic pieces. The transformer is shown setting on the "toroid helper," which is an old soldering iron handle, for flattening and rolling the relatively heavy wire turns against the inside surface. The assembly would not have been possible without this operation. I had to flatten and roll each and every turn as it was put on - very tedious. The source output terminal is the red binding post, screwed into the resonator post, which is solid copper at the top end first 1/2 inch or so. The rest is actually a hollow brass tube brazed to the top. Two different thicknesses of fish paper added up about right for a snug fit. On the right is a resonator. I had to cut off about 3/8" from the tubing end.
"Parts 2" is another view, showing some detail. The transformer's main winding is around 69 turns +/-1, until I do a final count. The other winding is the single-turn anti-phase one, for holder capacitance neutralization capability I want for possible crystal testing features. It's tucked in between the last two turns of the cold end of the main winding. You can see the hollow tube structure of the resonator, and on the unit, a 10-32 spacer inside, threaded to the tip threads of the binding post. The spacer helps to lock the post in, and provides for a compression screw at the end to pinch the mid-point foil against the tube edge, hopefully eliminating the need to solder it (TBD).
"Complete unit 1" shows the assembly with transformer mounted, and the end screw and washer foil clamp. The transformer is a very tight fit, and for protection of the wire, there will be a 1 or 2 mil layer of Kapton film around the post. That's all that can practically fit! You have to imagine how it would look when finally all wrapped in foil. Also, note the solder lug under the binding post. That's for signal monitoring and level detecting, depending on how things turn out. For my purposes, it will be connected to a 50 ohm resistor and cable to a BNC port, to measure with the SA.
"Complete unit 2" is a closeup side view. When everything is finally aligned, the three screws in the bushing side are tightened, compressing the fish paper against the post, so it stays put with respect to the bushing, against axial force and torque from working the binding post. The bushing will be the electrical and mechanical mount into the ground plane (method TBD), so the back end of the transformer won't need support. Note the gap between the bushing and the transformer. That's the tricky part, which will be to solder the bushing face perpendicular to a sheet of Cu foil, then slice out a hole from the other side of the foil, nice and clean. Then it's assembled with the foil tight against the transformer face, and wrapped all around, tightly conforming to the outside (and accommodating the wiring), and finally clamped (or soldered) to the back end of the post as mentioned above.
The primary inductance ended up at about 45.2 uH, and wire R about 120 milliohms. With better L readings, I've revised my A sub L estimate to a little below 10 nH, so it turns out the core seems to be very close to the T130-6, at 9.6 nH.
That's all for now. Enjoy.
Ed
