Reliability of valves/tubes - quiz question
 

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 ?
Please reply here

Answer tomorrow


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Reliability of valves/tubes - quiz question
 

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 ?
Please reply here

Answer tomorrow

In my field (audio amp repairs) actual valve heater failures are very
rare - Occasionally you see a case where the contact between valve pin
and internal riser is intermittent. I wouldnt like to guess at Colossus,
maybe one or two, possibly none. Of course valves ain't what they use
to be!

Ron

Reliability of valves/tubes - quiz question
 

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 ?
Please reply here

Answer tomorrow

In my field (audio amp repairs) actual valve heater failures are very
rare - Occasionally you see a case where the contact between valve pin
and internal riser is intermittent. I wouldnt like to guess at Colossus,
maybe one or two, possibly none. Of course valves ain't what they use
to be!

Ron

They are all old contemporary valves. I should have said how many failures
for whatever reason in those 2,500 per year ? considering that they are
powered up slowly from cold, to reduce that reason for failure .


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Reliability of valves/tubes - quiz question
 

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

Reliability of valves/tubes - quiz question
 

On Wed, 1 Oct 2008 10:35:21 +0100, "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 ?
Please reply here

http://www.mosweb.com/knowledgebase/tp5.htm
http://www.john-a-harper.com/FilamentHeating
About 100,000 hrs lifetime. No clue if that's mean, median, or
average. Ignoring the bell curve and assuming burned-in tubes without
infant mortality, that would be one failure every 40 hours for 2,500
tubes. With 8760 hrs/year, that's 219 failures per year.

However, that's not really true because the failures are not uniform.
With new tubes, there's a peak for early failures (infant mortality),
a long time with a very low failure rate, and then another big peak at
end-o-life, where filament thinning turns them into fuses.

I recall stats from the original Eniac, that was initially
experiencing a tube failure every 30 minutes of operation. Someone
finally decided to reduce the filament voltage from 6.3VAC to about
5.9VAC(?), which extended the lifetime dramatically by reducing metal
migration/thinning. Reduced filament voltage and temperature are not
a great idea for power tubes, but are well tolerated by digital tube
(flip-flop) circuits. I suspect Colossus uses a similar trick in
addition to inrush current control.

Answer tomorrow

Predicted or actual tube life?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Reliability of valves/tubes - quiz question
 

Jeff Liebermann wrote in message
...
On Wed, 1 Oct 2008 10:35:21 +0100, "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 ?
Please reply here

http://www.mosweb.com/knowledgebase/tp5.htm
http://www.john-a-harper.com/FilamentHeating
About 100,000 hrs lifetime. No clue if that's mean, median, or
average. Ignoring the bell curve and assuming burned-in tubes without
infant mortality, that would be one failure every 40 hours for 2,500
tubes. With 8760 hrs/year, that's 219 failures per year.

However, that's not really true because the failures are not uniform.
With new tubes, there's a peak for early failures (infant mortality),
a long time with a very low failure rate, and then another big peak at
end-o-life, where filament thinning turns them into fuses.

I recall stats from the original Eniac, that was initially
experiencing a tube failure every 30 minutes of operation. Someone
finally decided to reduce the filament voltage from 6.3VAC to about
5.9VAC(?), which extended the lifetime dramatically by reducing metal
migration/thinning. Reduced filament voltage and temperature are not
a great idea for power tubes, but are well tolerated by digital tube
(flip-flop) circuits. I suspect Colossus uses a similar trick in
addition to inrush current control.

Answer tomorrow

Predicted or actual tube life?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In the 40s Colossus was left on 24/7 on the recommendation of Tommy Flowers
, Dollis Hill engineer, for maximum filament life.

Answer tomorrow will be what Tony Sale actually experiences in running the
Bletchley colussus 7 days , only days , a week


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Reliability of valves/tubes - quiz question
 

"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
...
On Wed, 1 Oct 2008 10:35:21 +0100, "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 ?
Please reply here

http://www.mosweb.com/knowledgebase/tp5.htm
http://www.john-a-harper.com/FilamentHeating
About 100,000 hrs lifetime. No clue if that's mean, median, or
average. Ignoring the bell curve and assuming burned-in tubes without
infant mortality, that would be one failure every 40 hours for 2,500
tubes. With 8760 hrs/year, that's 219 failures per year.

However, that's not really true because the failures are not uniform.
With new tubes, there's a peak for early failures (infant mortality),
a long time with a very low failure rate, and then another big peak at
end-o-life, where filament thinning turns them into fuses.

I recall stats from the original Eniac, that was initially
experiencing a tube failure every 30 minutes of operation. Someone
finally decided to reduce the filament voltage from 6.3VAC to about
5.9VAC(?), which extended the lifetime dramatically by reducing metal
migration/thinning. Reduced filament voltage and temperature are not
a great idea for power tubes, but are well tolerated by digital tube
(flip-flop) circuits. I suspect Colossus uses a similar trick in
addition to inrush current control.

Answer tomorrow

Predicted or actual tube life?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In the 40s Colossus was left on 24/7 on the recommendation of Tommy
Flowers
, Dollis Hill engineer, for maximum filament life.

Answer tomorrow will be what Tony Sale actually experiences in running the
Bletchley colussus 7 days , only days , a week



I seem to recall reading that during the service time of the original
machine, not a single valve failed. Were they KT66s or 88s ...?

Arfa

Reliability of valves/tubes - quiz question
 

Arfa Daily wrote in message
...

"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
...
On Wed, 1 Oct 2008 10:35:21 +0100, "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 ?
Please reply here

http://www.mosweb.com/knowledgebase/tp5.htm
http://www.john-a-harper.com/FilamentHeating
About 100,000 hrs lifetime. No clue if that's mean, median, or
average. Ignoring the bell curve and assuming burned-in tubes without
infant mortality, that would be one failure every 40 hours for 2,500
tubes. With 8760 hrs/year, that's 219 failures per year.

However, that's not really true because the failures are not uniform.
With new tubes, there's a peak for early failures (infant mortality),
a long time with a very low failure rate, and then another big peak at
end-o-life, where filament thinning turns them into fuses.

I recall stats from the original Eniac, that was initially
experiencing a tube failure every 30 minutes of operation. Someone
finally decided to reduce the filament voltage from 6.3VAC to about
5.9VAC(?), which extended the lifetime dramatically by reducing metal
migration/thinning. Reduced filament voltage and temperature are not
a great idea for power tubes, but are well tolerated by digital tube
(flip-flop) circuits. I suspect Colossus uses a similar trick in
addition to inrush current control.

Answer tomorrow

Predicted or actual tube life?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In the 40s Colossus was left on 24/7 on the recommendation of Tommy
Flowers
, Dollis Hill engineer, for maximum filament life.

Answer tomorrow will be what Tony Sale actually experiences in running
the
Bletchley colussus 7 days , only days , a week



I seem to recall reading that during the service time of the original
machine, not a single valve failed. Were they KT66s or 88s ...?

Arfa



About 5 valves a year need replacing.

IIRC about 1,000 of them are thyratrons, 2 are needed for each single bit of
memory storage. The mark 1 did not have them and required running 2 loops of
paper tape , the mark 2 required only 1 paper tape loop


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Reliability of valves/tubes - quiz question
 

In rec.antiques.radio+phono 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 ?
Please reply here

Say, it runs 8 hours a day, every day... That is 2922 hours of operation a
year. By rough estimate, every 5 years the complete valve supplement will
be renewed. That is 500 valves a year. When it runs only 4 hours a day, it
will be half this number, etc.

--
Met vriendelijke groet,

Maarten Bakker.

Reliability of valves/tubes - quiz question
 

In rec.antiques.radio+phono N_Cook wrote:
About 5 valves a year need replacing.
IIRC about 1,000 of them are thyratrons, 2 are needed for each single bit of
memory storage. The mark 1 did not have them and required running 2 loops of
paper tape , the mark 2 required only 1 paper tape loop

I should have consulted both the life expectany figures of the tubes, and
the rest of the thread before answering too late. Is 5 valves a year a
long term average?

--
Met vriendelijke groet,

Maarten Bakker.

Reliability of valves/tubes - quiz question
 

On Thu, 2 Oct 2008 12:32:41 +0100, "N_Cook" wrote:

About 5 valves a year need replacing.

Very impressive. I thought it would be much worse.

IIRC about 1,000 of them are thyratrons, 2 are needed for each single bit of
memory storage. The mark 1 did not have them and required running 2 loops of
paper tape , the mark 2 required only 1 paper tape loop

That's cheating. Thyratrons are gas filled (usually hydrogen) low
pressure devices. They're also sometimes run with a relatively cold
cathode. The traditional failure mode is silicon and other impurities
in the filament slowly coating the cathode and ruining its ability to
emit electrons, is less of a problem with gas filled tubes such as
thyratrons. Thyratrons were probably chosen over the faster vacuum
tubes for that reason.

http://www.tnmoc.org/ColRbd.htm
"Mainly Mullard EF36 pentodes but also 6J5 triodes, 6V6
and 807 tetrodes and the GT1C thyratrons"

GT1C thyratron:
http://www.tubecollector.org/gt1c.htm
4V at 1.4A for the filament. So much for the cold cathode theory. I
guess that came later.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558