20 Jun
2011
20 Jun
'11
11:45 a.m.
On 2011 Jun 20, at 7:50 AM, dwight elvey wrote:
Hi
I needed to replace the nixie driver on one of my
HP counters. These are a real pain. They are hard to find
and if I want one, I have to buy 10 at $10+ each.
These are frustrating because there is a TTL part that
does exactly the same thing.
It blanks the display for values above 9 and takes a
TTL level input.
The part is the 74141. The only problem is that the
logic levels are inverted and wired differently. I piggy-backed
stacked a 7404, 74141 and a machine socket with some
wire and hot glue.
The 74141s are also hard to find but many can be found
on ebay at a resonable price.
I'm quite pleased with the result because I'd moved the
failed digit to the last location that rarely gets used.
It would only display even numbers for odd.
Now they all work :)
I've had a couple of those ICs fail in an HP counter too. I had a junk
board from another HP counter that I was able to scavenge replacements
from.
Those were fairly early MSI ICs (1967). There were several NIXIE
drivers being made in that period until the 74141 finally 'settled the
argument'.
http://www.cs.ubc.ca/~hilpert/e/nixieref/index.html
http://www.cs.ubc.ca/~hilpert/e/edte/HP5216A/index.html
The other funny parts HP made for use in those counters are the decade
counter chips (1820-0093 and 1820-0119) with an 11th state to represent
a blanked zero. When the counter is reset it is put into the
blanked-zero state. During the gate/count period, a given digit will be
unblanked if it sees any clock pulses, so at the end of the gate period
leading zeroes remain blanked while lower-order zeros are displayed.