[time-nuts] HP 5245L Question

[David Forbes]

At 9:00 PM +0000 1/9/10, <g4gjl at btopenworld.com> wrote:
>
>I wondered about replacing nixie tubes and associated drivers with 7 
>segment LEDs in one of my (already hacked) units, to make it more 
>reliable. I would use the BCD to drive the display, thus requiring a 
>new interface board to be designed. I wonder if anyone else has 
>considered such a radical remedy to the failing photocell problem?
>
>  In case anyone is wondering 'WHY BOTHER?', my defence is that I too 
>have an extensive collection of the plug ins, extending the 
>usefulness of the basic instrument way beyond my budget for more 
>modern equivalent instruments.
>
>Hope this question is not considered too far off topic for this forum.
>
>Peter Worrall

Peter,

The nixie tube is a wonderful thing. Surely you can't just find a 
couple extra counters on ebay and scavenge them for parts? That's 
what I did.

If you must redesign it, be aware that HP used 1950s pulsed counter 
methods in that counter. It's utterly different from anything you 
will find in a part with more than four legs. The circuitry has a lot 
more in common with their vacuum tube counters.

The most expedient method to replace the CdS photocell decoder would 
be to use a PC board with a bunch of diodes as a logic decoder. Just 
make the sense of the diode gates match that of the photocells, and 
copy the original 'AND gate' logic of the hybrid.

The storage method is non-obvious. It might require some extra chips 
if you do it the new-fangled way.

Nixies are still viable display elements, and they can be driven 
nicely with the TD62084 or the similar TI SN75468.
-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/