I think this is the problem: The base-emitter of the PNP is not shunted with a resistor (see note from Terry). The purpose of the base-emitter resistor is to provide a path for the leakage-current of the NPN predriver.
With the schematic as shown, roughly half of the NPN's leakage current goes thru the base of the PNP. That current is them multiplied by beta, which I think was around 130 from the datasheet. It's not a lot of current, but it could certainly contribute to unwanted glowing. Before you start hacking-up your PCB, can you try adjusting the timing of your anode drivers so there is some 'dead-time', say 50-100usec, after 1 anode is turned off, and the next one is turned on ? Also, if you can turn off all cathode drivers during the dead-time, that might help. This will ensure the tube is no longer ionized, and that should either reduce the unwanted glow or make it more difficult to re-ionize from leakage. And to be safe, dont turn off the anode & cathodes at exactly the same time (stagger by ~1usec); otherwise you could create a di/dt problem from the stray inductance of the wiring. Now, if that doesn't work, next thing to try is a true base-emitter resistor, for example, moving the connection of R22 to the other side of R21 (see Terry's note). I dont think the resistor values are critical as long as they are at least 100K and they are 1/4 watt (or larger). You dont want them to overheat P=Vcc^2/R, so with Vcc=160V, R=100K, a 1/4W resistor is at the limit. If your local Radio Shack store hasn't shut the doors yet, grab some resistors. (I just got some stuff last night at a 95% discount) -- 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 [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/ec792710-6aa8-459b-80d1-5cc6990d2dba%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
