Tube filiment voltage ???

[KA4HJH]

>      I remember (well I read that... I'm not THAT old...) that ENIAC
>used a reduced filiment voltage to prolong the life of the tubes so that
>the MTBF would be acceptable.
>Not that the tubes were unreliable... but with that many tubes in one
>place its a done deal that one is (statistically) sure to die at any
>time.
>
>    Other hand I've heard it said that this was done just to reduce HEAT.
>Thousands of tubes would do that also...

I just had to look this up.

18,000 tubes. Weighed 30 tons. Cost $486,840 in 1946. Of the 1847.8 
hours spent on "unscheduled engineering", 90% of that time was spent 
finding and replacing bad tubes. 19,000 were replaced in 1952 alone. 
I guess that HAD to be acceptable.


50 years later, it was replicated in silicon:

>The full ENIAC(TM)-on-a-Chip has been fabricated in a 0.5 micron, 
>triple metal, nwell CMOS process. The chip has a size of 7.44mm by 
>5.29mm and contains about 174,569 transistors.

http://www.ee.upenn.edu/~jan/eniacproj.html


Terry Bowman, KA4HJH
"The Mac Doctor"

ICQ: 45652354