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OT magnetron service life



 
 
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  #1  
Old December 1st 13, 05:59 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default OT magnetron service life

We recently purchased a new microwave oven from Sainsburys to replace
our 20 years plus old Toshiba ER-7700E which had developed an
intermittent display fault (requiring a slap on its side to resurrect
the display, implying a bad connector contact or dry joint).

Out of curiousity, I'd already googled for info on the durability of
microwave ovens and noted an oft quoted figure of 2,000 hours for the
magnetron. Since a conservative estimate of 15 minutes a day usage
over a 20 year period produced a figure of some 1,826 hours and I
suspect the microwave oven may be even older than 25 years, I thought
it only prudent to buy a cost effective replacement.

The model we bought was a Sainsbury's Stainless Steel 20 litre
"Special" with a rating of 800W reduced from 80 quid to 40 quid (with
another fiver knocked of the price by way of a good will gesture on
account we'd had to return it for an 'undamaged' replacement).

We chose this particular model on account of a recommendation by my
younger brother and SiL who had found it outperformed other more
expensive models that they'd had the misfortune to experience
(thankfully, with full refund policies, just a matter of
inconvenience).

The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.

Having finally established a replacement for the Toshiba a couple of
weeks ago, I've had the old microwave oven sat on my workbench with
the cover off so I could examine the controller board.

There didn't appear to be any sign of dry joints or capacitor rot so
it's quite possibly just a bad contact in one of the four or so plug
connectors to the board, each of which I reseated (several times).
This action may well have cured the intermittent display fault (I've
not seen any display problems with the few tests I've done since so it
looks promising).

However, the main reason as to why the old oven has spent so much
time perched on my workbench is that I've been wanting to run an
'efficiency test' which requires a suitable thermometer (ideally a
calibrated standard glass/liquid lab thermometer covering the range
-10 deg to 110 deg C). The half litre plastic jug of water is the easy
requirement to fulfil.

Today, after looking at suitable (but overpriced) alternatives in the
gardening accessories dept of our local Wilkinsons store, I finally
decided to 'wrench' our existing outdoor thermometer (which had been
bought it in Home Bargain last summer for the princely sum of 89
pence) off the masonary nail I'd used to attach it to the wall. It
turned out that I was able to riggle the masonary nail out of the
cement mortar joint without damaging the thermometer (score one for me
and nil to the retail trade practice of 'Seasonal Stocking').

Having finally collected my 'Test Equipment' together, the first item
I tested was the brand new "800W" oven. A 500ml jug of cold water was
heated up by 31 deg C with 120 seconds run time at full power. Using
the 4.18 joules per calorie approximation as my conversion factor, I
calculated an effective microwave power level of 540W. Strangely on
the low side for an oven with a specified 750 to 800W cooking power.

When it came to running the exact same test with the old oven (a 650W
rated oven according to the surpisingly large numbers of this model
still being advertised for private sale - we lost sight of the manual
many years ago so I was never quite sure of this and the model number
contains no real clue), the temperature rise was 30 deg C which, using
the same calculation, equates to a heating power of 522W, a mere
3.333% reduction compared to the new 750/800W microwave.

This rather begs the question, should I re-instate the Toshiba and
set the Sainsbury Special to one side as a spare or retire the old
oven permanently. For myself, it's a "No Brainer" since the Toshiba
controls are far and away the more 'advanced' with the additional
feature that the cancel button, unlike the SS, also acts as a silencer
for the "Cooking Completed" beeps (just 3 rather than the more
annoying 5 of the SS).

The one thing I _am_ mindful of is the possibility of reduced cathode
emission causing 'modeing' where the heating effect may be reduced
with high fat/low water content foodstuffs but with a 20 years plus
old 650W rated oven only being a mere 3.33% shy of the performance of
a brand new 750W oven, I'm left wondering whether any such
deterioration has taken place at all.

Like most such sources of "Expert Opinion" to be found via a google
search, I get the impression that most so called 'experts' are either
idiots or shills pushing a party line, in this case, one intended to
promote the sales of new, inferior, product.

IOW, does anyone here know if the "2,000 hour" figure that seems to
be parroted throughout the relevent fora have any basis in fact?
--
Regards, J B Good
  #2  
Old December 1st 13, 07:24 PM posted to uk.tech.digital-tv
Graham.[_2_]
external usenet poster
 
Posts: 1,500
Default OT magnetron service life

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

We recently purchased a new microwave oven from Sainsburys to replace
our 20 years plus old Toshiba ER-7700E which had developed an
intermittent display fault (requiring a slap on its side to resurrect
the display, implying a bad connector contact or dry joint).

Out of curiousity, I'd already googled for info on the durability of
microwave ovens and noted an oft quoted figure of 2,000 hours for the
magnetron. Since a conservative estimate of 15 minutes a day usage
over a 20 year period produced a figure of some 1,826 hours and I
suspect the microwave oven may be even older than 25 years, I thought
it only prudent to buy a cost effective replacement.

The model we bought was a Sainsbury's Stainless Steel 20 litre
"Special" with a rating of 800W reduced from 80 quid to 40 quid (with
another fiver knocked of the price by way of a good will gesture on
account we'd had to return it for an 'undamaged' replacement).

We chose this particular model on account of a recommendation by my
younger brother and SiL who had found it outperformed other more
expensive models that they'd had the misfortune to experience
(thankfully, with full refund policies, just a matter of
inconvenience).

The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.

Having finally established a replacement for the Toshiba a couple of
weeks ago, I've had the old microwave oven sat on my workbench with
the cover off so I could examine the controller board.

There didn't appear to be any sign of dry joints or capacitor rot so
it's quite possibly just a bad contact in one of the four or so plug
connectors to the board, each of which I reseated (several times).
This action may well have cured the intermittent display fault (I've
not seen any display problems with the few tests I've done since so it
looks promising).

However, the main reason as to why the old oven has spent so much
time perched on my workbench is that I've been wanting to run an
'efficiency test' which requires a suitable thermometer (ideally a
calibrated standard glass/liquid lab thermometer covering the range
-10 deg to 110 deg C). The half litre plastic jug of water is the easy
requirement to fulfil.

Today, after looking at suitable (but overpriced) alternatives in the
gardening accessories dept of our local Wilkinsons store, I finally
decided to 'wrench' our existing outdoor thermometer (which had been
bought it in Home Bargain last summer for the princely sum of 89
pence) off the masonary nail I'd used to attach it to the wall. It
turned out that I was able to riggle the masonary nail out of the
cement mortar joint without damaging the thermometer (score one for me
and nil to the retail trade practice of 'Seasonal Stocking').

Having finally collected my 'Test Equipment' together, the first item
I tested was the brand new "800W" oven. A 500ml jug of cold water was
heated up by 31 deg C with 120 seconds run time at full power. Using
the 4.18 joules per calorie approximation as my conversion factor, I
calculated an effective microwave power level of 540W. Strangely on
the low side for an oven with a specified 750 to 800W cooking power.

When it came to running the exact same test with the old oven (a 650W
rated oven according to the surpisingly large numbers of this model
still being advertised for private sale - we lost sight of the manual
many years ago so I was never quite sure of this and the model number
contains no real clue), the temperature rise was 30 deg C which, using
the same calculation, equates to a heating power of 522W, a mere
3.333% reduction compared to the new 750/800W microwave.

This rather begs the question, should I re-instate the Toshiba and
set the Sainsbury Special to one side as a spare or retire the old
oven permanently. For myself, it's a "No Brainer" since the Toshiba
controls are far and away the more 'advanced' with the additional
feature that the cancel button, unlike the SS, also acts as a silencer
for the "Cooking Completed" beeps (just 3 rather than the more
annoying 5 of the SS).

The one thing I _am_ mindful of is the possibility of reduced cathode
emission causing 'modeing' where the heating effect may be reduced
with high fat/low water content foodstuffs but with a 20 years plus
old 650W rated oven only being a mere 3.33% shy of the performance of
a brand new 750W oven, I'm left wondering whether any such
deterioration has taken place at all.

Like most such sources of "Expert Opinion" to be found via a google
search, I get the impression that most so called 'experts' are either
idiots or shills pushing a party line, in this case, one intended to
promote the sales of new, inferior, product.

IOW, does anyone here know if the "2,000 hour" figure that seems to
be parroted throughout the relevent fora have any basis in fact?




If you Google hard enough you will find that 600 odd watt ovens all
got upgraded overnight to 800 odd watt because the means of
calculating oven power changed. Think RMS vs Music Power ;-)

A question for you.
Are you saying that Sainsbury's sell an "own brand" microwave with a
stainless steel cooking cavity? I most have missed that when I was
looking.



--
Graham.

%Profound_observation%
  #3  
Old December 1st 13, 07:39 PM posted to uk.tech.digital-tv
Tim+
external usenet poster
 
Posts: 113
Default OT magnetron service life

Johny B Good wrote:


The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.


But does it go "ding"?

A very important attribute of any "proper" microwave. ;-)

Tim
  #4  
Old December 1st 13, 10:48 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default OT magnetron service life

On Sun, 1 Dec 2013 20:39:26 +0000, Tim+
wrote:

Johny B Good wrote:


The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.


But does it go "ding"?

A very important attribute of any "proper" microwave. ;-)


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.

If you're into your Chinese cuisine, I'm afraid "Chicken Ding" is off
the menu.
--
Regards, J B Good
  #5  
Old December 1st 13, 11:17 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default OT magnetron service life

On Sun, 01 Dec 2013 20:24:00 +0000, Graham. wrote:

====snip====


If you Google hard enough you will find that 600 odd watt ovens all
got upgraded overnight to 800 odd watt because the means of
calculating oven power changed. Think RMS vs Music Power ;-)

A question for you.
Are you saying that Sainsbury's sell an "own brand" microwave with a
stainless steel cooking cavity? I most have missed that when I was
looking.


I don't think they claimed the cavity was stainless steel, just that
the exterior finish was stainless steel (which still retains a
significant amount of paramagnetiism).

Try as I might, I couldn't find a model number, nor for that matter,
any user guide downloads. I think it was simply described as a
Sainsburys 800W 20 litre stainless steel microwave oven.
--
Regards, J B Good
  #6  
Old December 1st 13, 11:20 PM posted to uk.tech.digital-tv
Graham.[_2_]
external usenet poster
 
Posts: 1,500
Default OT magnetron service life

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

On Sun, 1 Dec 2013 20:39:26 +0000, Tim+
wrote:

Johny B Good wrote:


The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.


But does it go "ding"?

A very important attribute of any "proper" microwave. ;-)


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.

If you're into your Chinese cuisine, I'm afraid "Chicken Ding" is off
the menu.



Is this Sainsbury's oven badged "Russell Hobbs" by any chance?

On the subject of your power tests, I use one of those cheap
indoor/outdoor digital thermometers from Lidl/Aldi type shops.
External temperature probe that can be submerged, and it has a
resolution of half a degree c

Even if the absolute accuracy is questionable, you are only interested
in delta T, and the response time is quite good.

--
Graham.

%Profound_observation%
  #7  
Old December 1st 13, 11:43 PM posted to uk.tech.digital-tv
Graham.[_2_]
external usenet poster
 
Posts: 1,500
Default OT magnetron service life

On Mon, 02 Dec 2013 00:17:27 +0000, Johny B Good
wrote:

On Sun, 01 Dec 2013 20:24:00 +0000, Graham. wrote:

====snip====


If you Google hard enough you will find that 600 odd watt ovens all
got upgraded overnight to 800 odd watt because the means of
calculating oven power changed. Think RMS vs Music Power ;-)

A question for you.
Are you saying that Sainsbury's sell an "own brand" microwave with a
stainless steel cooking cavity? I most have missed that when I was
looking.


I don't think they claimed the cavity was stainless steel, just that
the exterior finish was stainless steel (which still retains a
significant amount of paramagnetiism).

Try as I might, I couldn't find a model number, nor for that matter,
any user guide downloads. I think it was simply described as a
Sainsburys 800W 20 litre stainless steel microwave oven.



Ah right.
SS interior was the most important atribute when I was looking. I came
across some that said stanless steel in the description but you needed
to see the machine and open the door to check.

--
Graham.

%Profound_observation%
  #8  
Old December 2nd 13, 03:47 AM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default OT magnetron service life

On Mon, 02 Dec 2013 00:20:32 +0000, Graham. wrote:

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

On Sun, 1 Dec 2013 20:39:26 +0000, Tim+
wrote:

Johny B Good wrote:


The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.


But does it go "ding"?

A very important attribute of any "proper" microwave. ;-)


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.

If you're into your Chinese cuisine, I'm afraid "Chicken Ding" is off
the menu.



Is this Sainsbury's oven badged "Russell Hobbs" by any chance?

On the subject of your power tests, I use one of those cheap
indoor/outdoor digital thermometers from Lidl/Aldi type shops.
External temperature probe that can be submerged, and it has a
resolution of half a degree c

Even if the absolute accuracy is questionable, you are only interested
in delta T, and the response time is quite good.


I used a cheap garden thermometer bought in the summertime from our
local Home Bargain store for the princely sum of, afaicr, 89pence.
It's the classic liquid in glass bulb capilary type with a max temp of
50 deg C (I can't recall what the minimum temp was - possibly -20 deg
C). The upper temperature limit was more than sufficient for this
test.

Usually the main problem with such cheap thermometers (including
electronic weather station types) is their calibration. They can quite
easily be off by a couple of degrees. However, as you say, this isn't
too important since we're only interest in the delta T. What's more,
in my case, even if the error varies with temperature, it still
allowed me to compare the performance between the two ovens which
confirmed my suspicion that there was very little to choose between
the two.

I'll swap the ovens around when I can avoid interference from the
XYL. If nothing else, I'm curious as to whether or not my reseating
the connectors has cleared the intermittent display fault (the only
problem that prompted the purchase of the "Sainsburys Special" in the
first place).
--
Regards, J B Good
  #9  
Old December 2nd 13, 07:12 AM posted to uk.tech.digital-tv
Jeff Layman[_2_]
external usenet poster
 
Posts: 668
Default OT magnetron service life

On 01/12/2013 18:59, Johny B Good wrote:
We recently purchased a new microwave oven from Sainsburys to replace
our 20 years plus old Toshiba ER-7700E which had developed an
intermittent display fault (requiring a slap on its side to resurrect
the display, implying a bad connector contact or dry joint).


(snip)

IOW, does anyone here know if the "2,000 hour" figure that seems to
be parroted throughout the relevent fora have any basis in fact?


We were given a present of a Hinari 800w microwave oven in 1994. It
worked very well, but at a critical time in 2001 started sparking inside
(it was just a small bit of carbonised food, but I didn't know that at
the time). It was replaced with a 900w Panasonic. I was certain it
didn't have the power output of the Hinari, IIRC, some weeks later I
measured it in a similar way to you, at about 725w. By this time I had
cleaned the Hinari and given it to my daughter, so couldn't measure its
power output.

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

--

Jeff
  #10  
Old December 2nd 13, 09:02 AM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 6,810
Default OT magnetron service life

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.
Also are you sure the actual power quoted is generated power? It might be
input power and efficiency does vary of course.
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.
If you like watching microwave abuse, plenty of that on the web. Myth
busters and Brainiac to name but two.

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

--
From the Sofa of Brian Gaff Reply address is active
"Johny B Good" wrote in message
...
We recently purchased a new microwave oven from Sainsburys to replace
our 20 years plus old Toshiba ER-7700E which had developed an
intermittent display fault (requiring a slap on its side to resurrect
the display, implying a bad connector contact or dry joint).

Out of curiousity, I'd already googled for info on the durability of
microwave ovens and noted an oft quoted figure of 2,000 hours for the
magnetron. Since a conservative estimate of 15 minutes a day usage
over a 20 year period produced a figure of some 1,826 hours and I
suspect the microwave oven may be even older than 25 years, I thought
it only prudent to buy a cost effective replacement.

The model we bought was a Sainsbury's Stainless Steel 20 litre
"Special" with a rating of 800W reduced from 80 quid to 40 quid (with
another fiver knocked of the price by way of a good will gesture on
account we'd had to return it for an 'undamaged' replacement).

We chose this particular model on account of a recommendation by my
younger brother and SiL who had found it outperformed other more
expensive models that they'd had the misfortune to experience
(thankfully, with full refund policies, just a matter of
inconvenience).

The fact that it used a rotary control knob to dial the time into the
electronic controller in a very similar fashion to that ancient
Toshiba's fine example of ergonomic perfection and the Which magazine
user reports being almost universally positive was the final clincher.

Having finally established a replacement for the Toshiba a couple of
weeks ago, I've had the old microwave oven sat on my workbench with
the cover off so I could examine the controller board.

There didn't appear to be any sign of dry joints or capacitor rot so
it's quite possibly just a bad contact in one of the four or so plug
connectors to the board, each of which I reseated (several times).
This action may well have cured the intermittent display fault (I've
not seen any display problems with the few tests I've done since so it
looks promising).

However, the main reason as to why the old oven has spent so much
time perched on my workbench is that I've been wanting to run an
'efficiency test' which requires a suitable thermometer (ideally a
calibrated standard glass/liquid lab thermometer covering the range
-10 deg to 110 deg C). The half litre plastic jug of water is the easy
requirement to fulfil.

Today, after looking at suitable (but overpriced) alternatives in the
gardening accessories dept of our local Wilkinsons store, I finally
decided to 'wrench' our existing outdoor thermometer (which had been
bought it in Home Bargain last summer for the princely sum of 89
pence) off the masonary nail I'd used to attach it to the wall. It
turned out that I was able to riggle the masonary nail out of the
cement mortar joint without damaging the thermometer (score one for me
and nil to the retail trade practice of 'Seasonal Stocking').

Having finally collected my 'Test Equipment' together, the first item
I tested was the brand new "800W" oven. A 500ml jug of cold water was
heated up by 31 deg C with 120 seconds run time at full power. Using
the 4.18 joules per calorie approximation as my conversion factor, I
calculated an effective microwave power level of 540W. Strangely on
the low side for an oven with a specified 750 to 800W cooking power.

When it came to running the exact same test with the old oven (a 650W
rated oven according to the surpisingly large numbers of this model
still being advertised for private sale - we lost sight of the manual
many years ago so I was never quite sure of this and the model number
contains no real clue), the temperature rise was 30 deg C which, using
the same calculation, equates to a heating power of 522W, a mere
3.333% reduction compared to the new 750/800W microwave.

This rather begs the question, should I re-instate the Toshiba and
set the Sainsbury Special to one side as a spare or retire the old
oven permanently. For myself, it's a "No Brainer" since the Toshiba
controls are far and away the more 'advanced' with the additional
feature that the cancel button, unlike the SS, also acts as a silencer
for the "Cooking Completed" beeps (just 3 rather than the more
annoying 5 of the SS).

The one thing I _am_ mindful of is the possibility of reduced cathode
emission causing 'modeing' where the heating effect may be reduced
with high fat/low water content foodstuffs but with a 20 years plus
old 650W rated oven only being a mere 3.33% shy of the performance of
a brand new 750W oven, I'm left wondering whether any such
deterioration has taken place at all.

Like most such sources of "Expert Opinion" to be found via a google
search, I get the impression that most so called 'experts' are either
idiots or shills pushing a party line, in this case, one intended to
promote the sales of new, inferior, product.

IOW, does anyone here know if the "2,000 hour" figure that seems to
be parroted throughout the relevent fora have any basis in fact?
--
Regards, J B Good



 




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