Half bridge of 40N60 IGBTs behind a 440 V TVS and a film capacitor, 37 inches of spark at first light. The driver gained primary current feedback here: cascaded current transformers at roughly 1:1000, an LM311 comparator into a 555 timer for over-current detection, and a 74HC109 JK flip-flop to synchronise the interrupter and feedback signals so a shutdown couldn’t land mid-RF-cycle. Ward counts DRSSTC-.5, two builds further down this chain, as his fourth. This one is his third.
Schematics and photos
DRSSTC-3 · 2spark 1 
DRSSTC-3 · 2spark 2 
DRSSTC-3 · 2spark 3 
DRSSTC-3 · 2spark 5 
DRSSTC-3 · 2spark 6 
DRSSTC-3 · 2spark 7 
DRSSTC-3 · 2spark 8 
DRSSTC-3 · 2spark 9 
DRSSTC-3 · 3spark 1 
DRSSTC-3 · 3spark 2 
DRSSTC-3 · 3spark 3 
DRSSTC-3 · 3spark 4 
DRSSTC-3 · 3spark 5 
DRSSTC-3 · 3spark 6 
DRSSTC-3 · 3spark 7 
DRSSTC-3 · 3spark 8 
DRSSTC-3 · Cage 1 
DRSSTC-3 · Cage 2 
DRSSTC-3 · DRSSTC OCDsch 
DRSSTC-3 · MMC 
DRSSTC-3 · Bottomlevel 
DRSSTC-3 · Bridge 2 
DRSSTC-3 · Interrupter 1 
DRSSTC-3 · Interrupter 2 
DRSSTC-3 · Primary 1 
DRSSTC-3 · Primary 2 
DRSSTC-3 · Primary 3 
DRSSTC-3 · Secondary 1 
DRSSTC-3 · Secondary 2 
DRSSTC-3 · Spark 1 
DRSSTC-3 · Spark 2 
DRSSTC-3 · Spark 3 
DRSSTC-3 · Spark 4 
DRSSTC-3 · Spark 5 
DRSSTC-3 · Spark 6 
DRSSTC-3 · Spark 7 
DRSSTC-3 · Toroids 
DRSSTC-3 · Wholecoil
Sources
This is the card from the driver tree, written from what the builder published. Send corrections through the forum.