Just got mine working today. The main FET was the problem all along. The transistor must have low Ciss and Qg. I had FETs that were much too capacitive and caused supply to draw amps of current. My proto board uses a 13.56MHz xtal, 1GX04, ADP3654 MOSFET driver, IRFR110 Nch (DPAK) to drive the coupled inductor/transformer. I took out the last LC section and have only two sections. Haven't yet hooked up rf-detect from 2nd tap or feedback path, just running it 'wide open'. Proto board is 2.5" x 3". Inductors pulled from broken Metcal PS2E supply.
Here's what I find. My switching reg is disabled, and I'm using a bench supply (xtal osc and driver regulated to 5V). The Metcal wand holder is magnetic and when solder hand piece/tip are placed in the holder, supply current goes to 220mA (Vs=14V). When hand piece is removed, current jumps immediately to 570mA and tip starts to heat up. To melt solder, Vs needs to be 16V or higher. At Vs=20V, current is 810mA. Wow this is quite reasonable, I can easily solder anything and the power is only 16W! STTC-126 tip. Surprisingly low current, low power. What I also find interesting is that after the tip heats up, it sort of self regulates and doesn't thermally run away - at least the supply current is quite stable. The FET (DPAK) doesn't have a heatsink yet but it gets hot when I remove wand and Vs up to 18V. Case is 90C. At idle (Vs=14V), case temp is low 50s. Might just attach a small heatsink with fins.
I had planned to use a 24V 2A brick supply, plug into a DC jack. That's still the plan. I had also planned to use a small plastic case from Amazon. 3" x 2.75" from Eightwood.