I'm just wondering how practical it would be to reproduce mike
Harrison's circuit with 74142's.
His primary design consideration was "only modern parts", simplicity &
cheap component costs...
While his design is logically simple, it's not simple to build..
He has 28 MPSA42 drivers. 1 of which is to drive the "10 hours" (1)
cathode, another is used to drive the blinking neon(s). That leaves 26
MPSA42 drivers that could be replaced with three 74142's used in place
of their CMOS decade counters. That's $21 to replace maybe $5 worth of
parts.. so we're +$15 at that point.
But the powersupply, which is the simplest part of Mike's circuit, would
need a complete overhaul. TTL parts need a solid +5vdc and won't work
with Mike's unisolated zener shunt logic supply. Also, as you say, the
74142 won't work at the 250vdc provided by the unisolated DC doubler
circuit. Probably I'd do the AC wall-wart, 7805 (or bucking switcher) &
boost switching supply... That right there takes away a lot of the
simplicity that the 74142's add to the circuit..
Probably explains why I haven't ever seen anybody do it. :) Still, an
interesting thought experiment.
-Adam
On 7/26/2011 12:13 PM, threeneurons wrote:
| 250vdc supply on his board would be too hot for a 74141 so probably
| too hot for a 74142.. Maybe a transformer supply..
|
| -Adam W7ATJ
250V is a tad too hot for a 74141. Western 74141s had zener clamps at
~60V, an from experience the Russian parts started to breakdown ~100V.
So if a nixie turns OFF ~130V, then the max supply is either 190V (130V
+60V), maybe 230V (130V+100V) for a Russian part. If you use a MPSA42,
which is good to 300V, then the supply can go upto 430V (assuming 130V
minimum sustain. 130V is only a ballpark number). Your anode resistors
might get a tad hot, if use that extreme of a voltage. In practice,
nixie supplies should be in the 180V to 200V range. 170V is the
absolute low end (direct drive only, too low for MUX'd circuits). 220V
probably the high end limit, if you use the 74141.
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