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OT magnetron service life



 
 
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  #11  
Old December 2nd 13, 10:56 AM posted to uk.tech.digital-tv
Paul Ratcliffe
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Posts: 2,442
Default OT magnetron service life

On Mon, 02 Dec 2013 08:12:01 +0000, Jeff Layman
wrote:

The Hinari continues to be used, and works perfectly even though it will
be 20 years old next June.


Mine is 22 years old and still going strong.
My mum's is 29 or 30 (can't quite remember) and suffers from slightly
reduced power output.
My brother's went to the tip after it started turning itself on at
random. It was perhaps 12-15 years old (can't really remember).
All are/were slightly different models of Panasonic.
  #12  
Old December 2nd 13, 10:59 AM posted to uk.tech.digital-tv
Paul Ratcliffe
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Posts: 2,442
Default OT magnetron service life

On Sun, 01 Dec 2013 23:48:47 +0000, Johny B Good
wrote:

Not 'ding', 5 (that's FIVE!) beeps when the countdown reaches zero.
The only way to cancel that unnecessarily long series of beeps is to
pre-empt them by cancelling before it reaches zero.


I always want to put a 6th, longer, one on the end.
  #13  
Old December 2nd 13, 11:18 AM posted to uk.tech.digital-tv
Mark Carver
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Posts: 7,562
Default OT magnetron service life

On 02/12/2013 11:56, Paul Ratcliffe wrote:
On Mon, 02 Dec 2013 08:12:01 +0000, Jeff Layman
wrote:

The Hinari continues to be used, and works perfectly even though it will
be 20 years old next June.


Mine is 22 years old and still going strong.
My mum's is 29 or 30 (can't quite remember) and suffers from slightly
reduced power output.


Yes, my parents one, a Belling bought in 1978 lasted over thirty years,
it died in 2010


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #14  
Old December 2nd 13, 01:53 PM posted to uk.tech.digital-tv
Graham.[_2_]
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Posts: 1,500
Default OT magnetron service life

On Mon, 02 Dec 2013 12:18:47 +0000, Mark Carver
wrote:

On 02/12/2013 11:56, Paul Ratcliffe wrote:
On Mon, 02 Dec 2013 08:12:01 +0000, Jeff Layman
wrote:

The Hinari continues to be used, and works perfectly even though it will
be 20 years old next June.


Mine is 22 years old and still going strong.
My mum's is 29 or 30 (can't quite remember) and suffers from slightly
reduced power output.


Yes, my parents one, a Belling bought in 1978 lasted over thirty years,
it died in 2010



Here is the one we had for about 25 years.

http://www.photomemorabilia.co.uk/Ph...owave_frnt.jpg

For some reason it was cheaper than others that had simple
electromechanical timers, so the choice was a no brainer. It even had
a temperature probe that plugged into a socket in the oven, not that I
ever remember using it.

It was still working when it was retired in favour of a smaller one,
even the thing that most concerned me, the membrane keypad, was still
perfect both esthetically and operationally.



--
Graham.

%Profound_observation%
  #15  
Old December 2nd 13, 04:15 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default OT magnetron service life

On Mon, 02 Dec 2013 11:59:08 GMT, Paul Ratcliffe
wrote:

On Sun, 01 Dec 2013 23:48:47 +0000, Johny B Good
wrote:

Not 'ding', 5 (that's FIVE!) beeps when the countdown reaches zero.
The only way to cancel that unnecessarily long series of beeps is to
pre-empt them by cancelling before it reaches zero.


I always want to put a 6th, longer, one on the end.


Yes, it's a tempting thought, isn't it? However, if I was going to go
to the trouble of 'patching' the firmware, that _wouldn't_ be my
priority. :-)
--
Regards, J B Good
  #16  
Old December 2nd 13, 05:04 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default OT magnetron service life

On Mon, 2 Dec 2013 10:02:07 -0000, "Brian Gaff"
wrote:

I think, answering in true politician format, that you are in fact asking
the wrong question here. Most microwaves have a turntable due to the uneven
nature of the power of heating in different areas due to standing waves
etc, So unless you can actually be sure that your arbitrary placement of the
heatable jug etc, is always going to get the best efficiency, you really
cannot tell what is going on in any realistic way. Food does vary in
conductivity of heat of course so always, the way anything behaves in a
given machine will be mostly trial and error.


That issue of uneven heating due to standing waves only really
applies to solid foodstuff. With a jug of water, it's not really an
issue unless you're planning on bringing it close to boiling point
temperature.

The Toshiba also includes a 'stirrer' driven, rather neatly by the
exhaust flow of the magnetron cooling air, as well as a turntable.

Also are you sure the actual power quoted is generated power? It might be
input power and efficiency does vary of course.


The input power isn't quoted as such, the rating plate simply states
"240v (_that_ must date it!) at 5.6A which is 1344VA. The actual input
power measured 1250W on the test.

I've currently got a watt meter in line with the power feed to the
new oven and noticed a reading of 1370W whilst heating a bowl of milk
to dump a portion of 'shreddies' into for my 'breakfast' early this
PM.

I suppose I aught to check this using a half litre of water in the
same plastic measuring jug used for the original tests to get a more
useful comparison. BTW, it was this practice of heating a bowl of milk
for my breakfast cereal that led me to suspect that the new oven
wasn't any better than the old one since I found myself having to use
the same 100 seconds heating time to heat said milk to a similar
temperature.

As for the original question, well, unless there is some catastrophic
failure caused by a fault in the high voltage feed or a flash over
Magnetrons last for ages. Early machines did have dire warnings about not
having stuff in the machine and definitely no metal etc, to stop the
standing waves damaging the machine, but I notice from the way mine behaves
if you do daft things, it just switches off the power and bleeps or pulses
the power to save the magnetron.


Yes, the power has to go somewhere, it can't build up indefinitely in
the system. The standing wave voltages will rise dramatically and the
surface currents in the cavity/waveguide/magnetron anode walls will
likewise build up increasing I squared R losses which can be tolerated
in the cavity and waveguide but far less so in the magnetron.

Undoubtedly, the output power of the magnetron will be reduced (which
aught to show as a reduced mains input power consumption - another
test to do) but not so much as to save the magnetron eventually
succumbing to the ill effects of the extra dissipation involved when
run under 'no load' conditions.

If you like watching microwave abuse, plenty of that on the web. Myth
busters and Brainiac to name but two.


Oh yes, I've watched many such 'interesting microwave experiments' on
youtube over the years. :-)


I think I'd use any microwave I was used to, but it does pay to use the
other one from time to time to stop things like capacitors fading with age.
Brian


Personally, I'd rather keep the new one in reserve rather than put up
with the unnecessary pain of switching between a well implemented
control algorithm and an ill-thought out one.
--
Regards, J B Good
  #17  
Old December 2nd 13, 05:58 PM posted to uk.tech.digital-tv
Graham.[_2_]
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Posts: 1,500
Default OT magnetron service life

On Mon, 02 Dec 2013 17:15:44 +0000, Johny B Good
wrote:

On Mon, 02 Dec 2013 11:59:08 GMT, Paul Ratcliffe
wrote:

On Sun, 01 Dec 2013 23:48:47 +0000, Johny B Good
wrote:

Not 'ding', 5 (that's FIVE!) beeps when the countdown reaches zero.
The only way to cancel that unnecessarily long series of beeps is to
pre-empt them by cancelling before it reaches zero.


I always want to put a 6th, longer, one on the end.


Yes, it's a tempting thought, isn't it? However, if I was going to go
to the trouble of 'patching' the firmware, that _wouldn't_ be my
priority. :-)


I'd need it to be proceeded by a polyphonic rendition of Lillibolero.
Makes you proud to be Irish... er I mean British.

--
Graham.

%Profound_observation%
  #18  
Old December 2nd 13, 09:34 PM posted to uk.tech.digital-tv
bilou[_2_]
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Posts: 20
Default OT magnetron service life


"Johny B Good" wrote in message
...
That issue of uneven heating due to standing waves only really
applies to solid foodstuff. With a jug of water, it's not really an
issue unless you're planning on bringing it close to boiling point
temperature.
snip...
Personally, I'd rather keep the new one in reserve rather than put up
with the unnecessary pain of switching between a well implemented
control algorithm and an ill-thought out one.
--

Nice OT discussion :-)
I totally agree that with a bowl of water position is not important.
It can be easily checked by repeating the measurement with various
positions.
A point that could induce errors is heating tlme of the magnetron.
To minimise its effect it is important to avoid too short tests.
5 minutes seems a minimum.
I would also use the new one during its waranty period.


  #19  
Old December 2nd 13, 09:53 PM posted to uk.tech.digital-tv
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Posts: 1,237
Default OT magnetron service life

On Sun, 01 Dec 2013 18:59:20 +0000, Johny B Good
wrote:

Haven't read the thread but this may be of interest..

http://www.dailymail.co.uk/news/arti...--Spencer.html
  #20  
Old December 2nd 13, 11:42 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default OT magnetron service life

On Mon, 2 Dec 2013 23:34:08 +0100, "bilou" wrote:


"Johny B Good" wrote in message
.. .
That issue of uneven heating due to standing waves only really
applies to solid foodstuff. With a jug of water, it's not really an
issue unless you're planning on bringing it close to boiling point
temperature.
snip...
Personally, I'd rather keep the new one in reserve rather than put up
with the unnecessary pain of switching between a well implemented
control algorithm and an ill-thought out one.
--

Nice OT discussion :-)
I totally agree that with a bowl of water position is not important.
It can be easily checked by repeating the measurement with various
positions.
A point that could induce errors is heating tlme of the magnetron.
To minimise its effect it is important to avoid too short tests.
5 minutes seems a minimum.
I would also use the new one during its waranty period.


Yes, this latter point is worth considering. I must admit that,
despite the 'annoyance factor', I suppose we owe it to Sainsburys to
'properly' test their warranty, if only for a few months to reveal any
design/manufacturing deficiencies. However, I do want to run the old
one for a week or two to verify whether reseating the connectors has
cleared the intermittent display fault.

With regard to the cathode warm up time on the magnetron, the Toshiba
oven seems to require some 5 or 6 seconds after startup before it's up
to power (which rather spoils the cooking time accuracy for time
settings below 30 seconds - and makes a mockery of the 10 second time
setting).

What the cathode heat up time does to the 5 second minimum time
setting that's possible with the new Sainsburys one must be to
effectively reduce it to no more than 1 or 2 second's worth (the
countdown starts immediately after pressing the start button - there's
no obvious pause).

In either case, a 2 minute test run will be sufficiently accurate
enough for my purpose. If anything, I suspect the comparitive test
will favour the new oven over the old (the new one seems to need less
heater warmup time than the old).

I suppose I could set a 130 second time and cancel when it reaches
the 5 seconds remaining point in the Toshiba's case and similarly with
the new oven, cancelling it with 8 seconds to go in order to take some
account of this 'dead time' in the cycle.

I won't bother now with repeating the tests since I've arleady nailed
the thermometer back onto the wall. With regard to trying different
positions of the jug of water, I'd already done that by placing it
slightly offcentre on the turntable (something I've always done from
the off). I did read this piece of advice very recently either in the
user guide or, more likely, in an internet article on the subject of
cooking with microwave ovens. It was nice to see my thinking on this
matter of placement being validated elsewhere. :-)
--
Regards, J B Good
 




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