Nixie driver chip question

[TChesek@Epix.Net]

Thanks to all for their assistance with my question and especially to Alan
for a greatly detailed answer.

Tom K3TVC


----- Original Message ----- 
From: "Alan 'A.J.' Franzman" <a.j.franzman at VERIZON.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Monday, March 20, 2006 7:37 PM
Subject: Re: [HEATH-TEMPE] Nixie driver chip question


> > Date:    Sun, 19 Mar 2006 11:07:51 -0500
> > From:    "Tom K3TVC" <tchesek at EPIX.NET>
> >
> <snip>
> > I came across a website listing truth tables for the 7441, 7441A, 7441B,
> > 74141 chips and there are differences. Is there anyone who has used a
> > substitution for the 7441B or knows if the differences in these chips
> > have any impact on these counters?
>
> The differences are as follows:
> The 74141 has protective zener diodes at its outputs (approx. 55-60 volts)
> which 7441 lacks.
> The 74141 has a poorly-thought-out blanking feature which is rarely used
(and
> even more rarely works as intended, due to the aforementioned zeners.)
> To (attempt to) blank a 74141, input a binary code greater than 9 (1001
bin).
> If your nixies and supply voltage are exactly right, the nixie will go
out.
> But what usually happens is the 60 volt zener drop is insufficient to
> extinguish the nixie, and all digits light dimly at the same time, forming
an
> indecipherable blob. Many pieces of equipment using 74141s will often
power up
> with one or more digit driver modules in an illegal or indeterminate state
and
> present such a display until they are reset.
>
> The 7441 does not blank. If a binary code greater than 9 is input to a
7441,
> the result is dependent on the exact make/revision of the chip. Some will
give
> 2 outputs active simultaneously, others will start counting again from
zero
> (i.e. 1010 bin = 0 dec, etc.), and others will give "8" for the evens and
"9"
> for the odds above 1001 bin. I do not know of any equipment designed to
take
> advantage of any of these odd states for illegal inputs to a 7441. Thus, I
> don't know of any case where replacing a 7441 with a 74141 would cause a
> malfunction.
>
> The Russian K or KM 155ID1 chips are identical in function to the 74141,
> except that the output transistors and protective zeners are rated about
100
> volts - making the blanking function nearly always work correctly. This
may be
> a rare case where the Russian copy is actually better than the original.
> However, there is a slight mechanical difference. Russian ICs and printed
> circuits of the period were based on a 2.50 mm grid as opposed to our 0.1
inch
> (2.54 mm) grid. This means that the legs of the IC may need to be tweaked
> slightly to fit properly in a western socket or PCB. It's not usually a
> problem with small ICS like these, but can be a major headache with larger
> chips as the difference accumulates over longer rows of pins.
>
> Best regards,
>
> Alan "A.J." Franzman
>
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