22 Dec
2007
22 Dec
'07
1:46 p.m.
On Sat, 22 Dec 2007, Tom Peters wrote:
The Burroughs spec sheets talk about the series anode
R recommended for each
of three types of tubes; for the B-7971 they say 1.8k. Does your suggestion
eliminate the need for a anode resistor?
I don't know about the spec sheet, but typically with segmented gas discharge
displays like this, one uses a series resistor for each segment/cathode so that
each segment gets a uniform current regardless of how many segments are on.
With a single anode resistor each segment gets a variable current for
different characters/segment-patterns (unless the tube has somehow been
designed to limit this variability within the typical character set).
With NIXIEs - where there is only one of the 10 cathodes on at any given time
- a single anode resistor can service all 10 cathodes. (Arguably, or
pedantically speaking, the 7971 isn't a NIXIE.)
.. experiment with just the tube, power supply, some resistors, some
switches/breadboard, and a (milli-)ammeter to see how it looks lit up,
.. a little fun in-and-of-itself.
.. then replace the switches with transistors.
Note that if you do anode switching for multiplexing you also need some high
voltage isolation (another transistor&c. or a capacitor) between the logic and
the base of the anode driver transistor.