Interesting question! Certainly if one was going to use it on a 'high' voltage, like one does with a neon bulb for example, one would definitely use a current limiting resistor. However, in the case shown here where the device is running at this low voltage level, then I don't think it is necessary. When building up this circuit, I had no idea what 'HT' to use for the display, although I knew it was very low, so started off by connecting it up to a 0-20V PSU. Using this, I was able to slowly ramp it up and note when the display fluorescent anode started to glow. Around 9 volts if I recall correctly. Taking it slowly up to about 20 volts, (the max . for the PSU) then it was about the same brightness as one would see on one of these displays in normal use. Hence, I don't think at these voltages a limiting resistor is necessary and therefore didn't use any for the demo. you've seen. Hope this helps!
@@lishaton I've seen circuits where sometimes they are used and sometimes not which is why I ask. I think in most cases, the current draw of the anodes/grids is low enough such that resistors are not needed. I suppose one could measure the current to be sure. I've seen 10k resistors being used when driven by NPN, but that is because it is a common collector configuration. Thank you for responding.
Thanks for another great video Chris very nice construction
Thank you Clare!
Hi, shouldn't there be current limiting resistors on the PNP collectors?
Interesting question! Certainly if one was going to use it on a 'high' voltage, like one does with a neon bulb for example, one would definitely use a current limiting resistor. However, in the case shown here where the device is running at this low voltage level, then I don't think it is necessary.
When building up this circuit, I had no idea what 'HT' to use for the display, although I knew it was very low, so started off by connecting it up to a 0-20V PSU. Using this, I was able to slowly ramp it up and note when the display fluorescent anode started to glow. Around 9 volts if I recall correctly. Taking it slowly up to about 20 volts, (the max . for the PSU) then it was about the same brightness as one would see on one of these displays in normal use. Hence, I don't think at these voltages a limiting resistor is necessary and therefore didn't use any for the demo. you've seen. Hope this helps!
@@lishaton I've seen circuits where sometimes they are used and sometimes not which is why I ask. I think in most cases, the current draw of the anodes/grids is low enough such that resistors are not needed. I suppose one could measure the current to be sure. I've seen 10k resistors being used when driven by NPN, but that is because it is a common collector configuration. Thank you for responding.