High- to low-voltage flash trigger circuit, from Sam Goldwasser's Electronics Repair FAQ:
5.1V zener diode
4M carbon resistor, 1/4 W (2)
22nF, 1000V capacitor
1N4148 signal diode
400V 1A triac (any will do)
I paid a visit to Alexan and, wonder of wonders, they had a new display: 22 nF, 1000V capacitors. In this photo (taken with a reversed 50mm lens), frolicking with zener diodes, Teccor triacs, and resistors:
I also bought correct-valued resistors and zener diodes (4.3M-ohms, 5.1V zeners), although the circuit worked fine previously with values that were way out of line.
A completed circuit (much neater than my earlier attempt):
Low-voltage trigger circuit installed inside Vivitar 283 (trigger voltage is now 3.5 volts, down from 110 volts, which is extra-extra safe):
The flash in all its glory..
With infinitely-variable power! (see hand-labeled "infinitely variable flash power adjustment"):
Professional external power supply cord! (some discarded extension cord, soldered directly to the flash main board):
And the non-Quantum power supply (saves a ton on AA batteries, and lasts forever):