Yes; for a given segment, there are tube-to-tube variations in segment current for a given voltage. The data below is for 8 tubes, for segment #1.
At 200uA, the voltage varies from 127 to 138V. At 6mA, the voltage varies from 169 to 181V Using just a resistor for setting the current will result in large variations across tubes and supply-voltage. That's why I use current-regulators on each cathode. It's probably overkill, but given the ridiculous pricing for b7971's, I'm not taking any chances. I have no spares for my 8-tube clock; just 2 tubes that have a shorted or dead segment. I have no idea what happens over time, but I suspect that as tubes age the current, hence the brightness, decreases for a given voltage. In a few years, I will retake the data and see what has happened. This clock went into service in 2017. 0.2 0.5 1 2 3 4 5 5.5 6 <-- Current 130 133 138 145 152 159 167 170 172 <--- Tube 1 135 138 143 151 158 166 174 178 181 134 137 142 150 158 166 174 178 180 138 138 140 145 151 158 164 169 172 137 138 142 148 156 163 172 176 180 135 136 140 147 154 162 171 174 177 131 134 138 144 151 158 166 170 173 127 130 134 141 147 155 162 166 169 <--- Tube 8 -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/de909caa-8df4-4214-8109-0c4d480681bc%40googlegroups.com.
