N_Cook wrote:
Ron(UK) wrote in message
...

N_Cook wrote:

As far as heaters are concerned. I went to a lecture by Tony Sale of
Colossus rebuild fame
http://www.codesandciphers.org.uk/lorenz/mk2.htm
About 2,500 valves in this computer.
They power up Colossus each day via a motorised variac.

How many valve failures a year, due to failed heaters in those 2,500,
would you expect ?

Get thee to a good reference library and examine issues of the Proceedings
of the IRE from about 1945 through 1955 -- there will be a number of
articles specifically addressing this issue, with solid numbers and
derived mathematics, from research on test beds as well as data from
Eniac and many other contemporaneous large digital machines.

Michael