[time-nuts] HP 5245L Question

[paul swed]

As I have described the replacement. Its simple and will work.
It eliminates the traditional transistor FF which I agree is much like the
vacuum tubes.
Further the decoding is not BCD its something stranger more like a grey
code.
But the counter is bcd on the board. But the 7490, 7475, and 7447 eliminate
all of that.
Been troubleshooting a 5248 M someone grabbed teh oscilator and A26 board
from it.
The a26 board was replced with 2 cmos chips and 1 transistor.
Now I am at the counter gate. Darned if I don't have an issue in the dreaded
tunnel diodes area. Such a lucky day for me.
Need to cleanup and solder in the pseudo a26 board so I can more easily work
on the gate.
Regards

On Sat, Jan 9, 2010 at 6:37 PM, David Forbes <dforbes at dakotacom.net> wrote:

> 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/
>
>
>
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