design note · Misc · computed
FIG. 20YI toroid is a 1/4-1/2-3/4-1:1 SCR tap ladder; the step-up is the grounded 41/42 VIC transformer after Q9; SCR ladder ratchets up within each 120 Hz hump
Amends #3515. Scotchn (Discord #neuralstan20-testing 2026-11-04) confirms: toroid primary 400 T vs secondary coils 100 T each gives at most 1:1 at the top tap; "the stepping up is post the gate SCR via the grounded P:S before the diode" (VIC primary 41 / secondary 42, then blocking diode 14). Resolves the discrepancy flagged in #3515 against US 4,936,961's "toroidal pulsing coil ... step-up in excess of five times": in 20YI that step-up role is taken by 41/42, not the tap toroid. Derived (my analysis, not on the sheet): SCRs rectify the toroid secondary taps (only forward portions pass to node 58). Upward level change commutates naturally: firing a higher tap lifts node 58 above the lower tap's anode and reverse-biases the conducting lower SCR. Downward change cannot commutate mid-hump: the lower SCR stays reverse-biased until the unfiltered 120 Hz rail falls toward zero and the latched SCR drops below holding current (same rail-commutation logic as #3363). So the ladder ratchets up within a hump and resets at each valley. Same architecture as the 423 DA (1994) relay-tapped VIC primary ladder (#3368): amplitude chosen on the primary side, step-up and diode after. Not yet tested on a bench or in simulation.
Basis
- Recorded
- Published
- 4 Nov 2026
- Stanbot
- v3
- Source Ref
- FIG. 20YI (c)1982 page G34; Scotchn Discord 2026-11-04; notebook #3515, #3363, #3368
- Notebook Id
- 3516
- Device Slug Unmapped
- hgg
20YI SCR-ladder commutation amplitude-ladder scotchn