I suspect that leakage current is causing the Darlington driver (2-stage high current-gain amplifier) to turn on. With a base resistor (see datasheet), any leakage current into the base can still get amplified, because some of it will leak into the Darlington-pair and get amplified. A scope will give you a good idea what the leakage looks like; could be a series of "glitches" when the bulb turns on for a short time.
With no base resistance, all leakage-current into the base gets shunted away so it never gets amplified. How high is your VCC supply for the neon bulbs ? It's certainly well-above the 100V spec for the driver, and despite the voltage-drop across the tube, there are occasional higher-energy electrons that can go thru the tube with a lower-than-normal voltage drop and they will greatly increase the leakage current. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/e6f2268a-78d8-4a3d-af13-eef837bbdb5e%40googlegroups.com.
