Re: Square root of a negative rral value

robin wrote:

"Terence" <tbwright@xxxxxxxxx> wrote in message

robin wrote:

"Terence" <tbwright@xxxxxxxxx> wrote in message

We used the Mercury computer for trajectory calculations.
First thing, was to walk into the computer with a box of double
triodes valves, unplug and replace any of the thousands with no
filaments visibly lit (while in standby mode).

Valves don't fail like that.
Even thousands of them.
Valves used in computers failed because of low emission, or
rarely because of some internal failure such as a short-circuit.
Recall ENIAC? The pessimists predicted that it would never work,
but it did.

Valve computers of the time could run for days and weeks without failure.

Robin, you missed the pint.

I have not missed the point.

If JUST ONE valve fails the computer isn't going to be usefl.
There were thousands of the (d...) things, but luckily all in nice
rows you could look along.
If one was "off" or "funny-looking" you replaced it. They were mainly
one valve per memory register bit (on/off). Occasionally you would
have to change two, so you took a box of them.
But you had to check, because after your time was up, someone else was

As I said, valve computers of the time were designed to run
for days at a time without fault. Valves used in computers did NOT fail with
blown heaters. I have the weekly serviceability returns of one such computer,
and there were others in the field with better reliabilty than that one.
What did fail from time to time were resistors and capacitors,
of which there were about five times more than there were valves.
Regular maintenance caught most of those before they developed into a fault.

Here I have Roland keyboards and amplifier equipment for making music
disc recordings.
On shelves are recent duds and new unused special quality 12AX7
"audio" valves, (still built today). They still don't last long!

I still have the valve radio that my late father purchased in the 1930s.
In all that time, only one valve failed.
Of another that he purchaed in 1956, only one valve failed.

Its fairly well known in the electronics industry that component failure is intentionally designed in (designed just good enough but not too good). I hope they werent in that mode of thinking that early :(


Gary Scott
mailto:garylscott@sbcglobal dot net

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