On 1/4/2014 8:08 AM, Leif Neland wrote:
Phil Allison skrev:

Same idea as using a glass of water and a thermometer test the power
RF power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

Measure the temperature of the cold water, then measure the time for it
to boil.

Preferably in a microwave-safe plastic container.

I measured the power of my previous oven to 230W...

Leif

When I did similar tests, I found the order of magnitude was right,
but the result depended on the shape and volume of the mass of water
and position in the oven.

It's easy to imagine that the microwaves bounce around and most of the
energy ends up
in the water. Wonder how accurate that model?
Wonder what the "official" water configuration is when they determine
the spec?

"mike" wrote in message ...

On 1/4/2014 8:08 AM, Leif Neland wrote:
Phil Allison skrev:

Same idea as using a glass of water and a thermometer test the power
RF power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

Measure the temperature of the cold water, then measure the time for it
to boil.

Preferably in a microwave-safe plastic container.

I measured the power of my previous oven to 230W...

Leif

When I did similar tests, I found the order of magnitude was right,
but the result depended on the shape and volume of the mass of water
and position in the oven.

It's easy to imagine that the microwaves bounce around and most of the
energy ends up
in the water. Wonder how accurate that model?
Wonder what the "official" water configuration is when they determine
the spec?

I've seen that method used before. I had an article about measuring
microwave oven power. You of course measure the increase in temperature
after running then microwave oven for a predetermine time at full power,
with a measured amount of water (distilled) in the direct center of the
oven. You could google it.

Shaun

"Leif Neland"
Phil Allison
Same idea as using a glass of water and a thermometer test the power RF
power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

** Should be OK with a glass tube and red liquid type.


Measure the temperature of the cold water, then measure the time for it to
boil.

** Bad idea.

Takes far too long, when boiling first begins is not clear and lots of heat
is lost to the air and evaporation.


I measured the power of my previous oven to 230W...

** Using half a litre in a plastic jug for two minutes, I got the answer to
within 10% with a 700W rated oven.

Having a K-type bead thermocouple and digital temp meter made the job easier
too.



..... Phil

"Phil Allison" wrote in message ...


"Leif Neland"
Phil Allison
Same idea as using a glass of water and a thermometer test the power RF
power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

** Should be OK with a glass tube and red liquid type.


Measure the temperature of the cold water, then measure the time for it to
boil.

** Bad idea.

Takes far too long, when boiling first begins is not clear and lots of heat
is lost to the air and evaporation.


I measured the power of my previous oven to 230W...

** Using half a litre in a plastic jug for two minutes, I got the answer to
within 10% with a 700W rated oven.

Having a K-type bead thermocouple and digital temp meter made the job
easier
too.

You don't run it till boiling! once you get close to boiling point a lot of
extra energy is required to raise it further and make it boil. What you do
is run a glass of cold distilled water measured (temp and volume) in a
container, you could use several stacked Styrofoam cups for insulation and
cover the top with Styrofoam so that the heat generated does not escape and
run the oven till the temperature increase 20 to 50 degrees or so, then
measure the temp, the information will have an equation to convert degrees
rise to microwave power. Google the method - I haven't looked it up lately.

Shaun



..... Phil

On 01/04/2014 06:21 PM, Shaun wrote:


"Phil Allison" wrote in message ...


"Leif Neland"
Phil Allison
Same idea as using a glass of water and a thermometer test the power
RF power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

** Should be OK with a glass tube and red liquid type.


Measure the temperature of the cold water, then measure the time for
it to boil.

** Bad idea.

Takes far too long, when boiling first begins is not clear and lots of
heat
is lost to the air and evaporation.


I measured the power of my previous oven to 230W...

** Using half a litre in a plastic jug for two minutes, I got the
answer to
within 10% with a 700W rated oven.

Having a K-type bead thermocouple and digital temp meter made the job
easier
too.

You don't run it till boiling! once you get close to boiling point a
lot of extra energy is required to raise it further and make it boil.
What you do is run a glass of cold distilled water measured (temp and
volume) in a container, you could use several stacked Styrofoam cups for
insulation and cover the top with Styrofoam so that the heat generated
does not escape and run the oven till the temperature increase 20 to 50
degrees or so, then measure the temp, the information will have an
equation to convert degrees rise to microwave power. Google the method
- I haven't looked it up lately.

Shaun



.... Phil

That is not how a calorimeter works. The load must be enclosed in liquid
and must perfectly match the RF output so it absorbs all the energy.
Then the temperature should be a very accurate way to measure power. It
must be a closed, water cooled load.

http://electro-impulse.com/techinfo/calorimeters.htm

"Shaun" wrote in message ...



"Phil Allison" wrote in message ...


"Leif Neland"
Phil Allison
Same idea as using a glass of water and a thermometer test the power RF
power of a microwave oven.

Just don't leave the thermometer in the microwave oven with the power on.

** Should be OK with a glass tube and red liquid type.


Measure the temperature of the cold water, then measure the time for it to
boil.

** Bad idea.

Takes far too long, when boiling first begins is not clear and lots of heat
is lost to the air and evaporation.


I measured the power of my previous oven to 230W...

** Using half a litre in a plastic jug for two minutes, I got the answer to
within 10% with a 700W rated oven.

Having a K-type bead thermocouple and digital temp meter made the job
easier
too.

You don't run it till boiling! once you get close to boiling point a lot of
extra energy is required to raise it further and make it boil. What you do
is run a glass of cold distilled water measured (temp and volume) in a
container, you could use several stacked Styrofoam cups for insulation and
cover the top with Styrofoam so that the heat generated does not escape and
run the oven till the temperature increase 20 to 50 degrees or so, then
measure the temp, the information will have an equation to convert degrees
rise to microwave power. Google the method - I haven't looked it up lately.

Shaun



Here is the Method from RepairFAQ from Sam:



7.1) Testing the oven - the water heating test


The precise number of degrees a known quantity of water increases in
temperature for a known time and power level is a very accurate test of
the actual useful microwave power. A couple of minutes with a cup of
water and a thermometer will conclusively determine if your microwave
oven is weak or you are just less patient (or the manufacturer of your
frozen dinners has increased their weight - sure, fat chance of that!)

You can skip the heavy math below and jump right to the final result
if you like. However, for those who are interested:

* 1 Calorie (C) will raise the temperature of 1 gram (g) of liquid water
exactly 1 degree Centigrade (DegC) or 9/5 degree Fahrenheit (DegF).

* 1 Calorie is equal to 4.184 Joules (J) or 1 J = .239 C.

* 1 Watt (W) of power is 1 J/s or 1 KW is 1000 J/s.

* 1 cup is 8 ounces (oz) which is 8 x 28.35 g/oz = 226.8 g.

* 1 minute equals 60 s (but you know this!).

Therefore, in one minute, a 1 KW microwave oven will raise the temperature
of 1 cup of water by:

T(rise) = (60 s * 1000 J/s * .239C/J * (g * DegC)/C)/(226.8 g) = 63
DegC.

Or, if your prefer Fahrenheit: 114 DegF.

To account for estimated losses due to conduction, convection, and imperfect
power transfer, I suggest using temperature rises of 60 DegC and 109 DegF.

Therefore, a very simple test is to place a measured cup of water in the
microwave from the tap and measure its temperature before and after heating
for exactly 1 minute on HIGH. Scale the expected temperature rise by the
ratio of the microwave (not AC line) power of your oven compared to a 1 KW
unit.

Or, from a Litton microwave handbook:

Heat one Liter (L) of water on HIGH for 1 minute.

Oven power = temperature rise in DegC multiplied by 70.

Use a plastic container rather than a glass one to minimize the needed
energy loss to raise its temperature by conduction from the hot water.
There will be some losses due to convection but this should not be that
significant for these short tests.

(Note: if the water is boiling when it comes out - at 100 DegC or 212 DegF,
then the test is invalid - use colder water or a shorter time.)

The intermediate power levels can be tested as well. The heating effect of
a microwave oven is nearly linear. Thus, a cup of water should take nearly
roughly twice as long to heat a specific number of degrees on 50% power or
3.3 times as long on 30% power as on full power. However, for low power
tests, increasing the time to 2 minutes with 2 cups of water will result
in more accurate measurements due to the long period pulse width power
control use by microwave ovens which may have a cycle of up to 30 seconds.

Any significant discrepancy between your measurements and the specified
microwave power levels - say more than 10 % on HIGH - may indicate a
problem.
(Due to conduction and convection losses as well as the time required to
heat the filament of the magnetron for each on-cycle, the accuracies of
the intermediate power level measurements may be slightly lower).

Shaun

I wanted to reply to this when you first posted it but I couldn't for
whatever reason. ****ing thing. As you can see I am not posting from
google, which I no longer capitalize !!!! LOL

Anyway, what characterizes ANY part for the transmission of audio is
linearity. Even though the gate of a MOSFET is driven wildly different
than the base of a BPT, linearity of gain fro the very small signal to
the very large signal is the prime. We used to look at the hfe and HFE
gain curves of bipolars in the old days, not it is different.

Any kinds of spurious **** like oscillations would be no good in
switcxhers as well. the thing is, switchers somethimes have a gain curve
that is like, made to be on or off.

An audio transistor must operate in the analog range, that means the
gain curve should be as flat as possible through the operating current
range.

The same is true of a MOSFET.

On 05/01/2014 07:53, Jeff Urban wrote:
I wanted to reply to this when you first posted it but I couldn't for
whatever reason. ****ing thing. As you can see I am not posting from
google, which I no longer capitalize !!!! LOL

Anyway, what characterizes ANY part for the transmission of audio is
linearity. Even though the gate of a MOSFET is driven wildly different
than the base of a BPT, linearity of gain fro the very small signal to
the very large signal is the prime. We used to look at the hfe and HFE
gain curves of bipolars in the old days, not it is different.

Any kinds of spurious **** like oscillations would be no good in
switcxhers as well. the thing is, switchers somethimes have a gain curve
that is like, made to be on or off.

An audio transistor must operate in the analog range, that means the
gain curve should be as flat as possible through the operating current
range.

The same is true of a MOSFET.


Ah at last , thanks, a pertinent reply to my original question. I was
wondering if it was a larger area of silicon so the heat can migrate out
of the die quicker. So from what you say a non-audio switcher mosfet
could be used for analogue but the power rating would have to be derated
and no other qualification for such use, anymore than usual precautions
you would use for a switcher situation. I suppose the amount of derating
would then depend on the type of use bass amp v GP audio amp, dance
music v classical music etc

"Nutcase Kook is yet another pig ignorant pommy ****"


Other than p channel in this case, same for BUZ901P nch
eg BUZ906P 200V, 8A ,datasheet says
"POWER MOSFETS FOR
AUDIO APPLICATIONS"
but also
"FEATURES ... (for use in)
HIGH SPEED SWITCHING ... "


** The Semelab app note makes it pretty clear there is a HUGE difference
between "switching" and audio ( ie lateral) power mosfets.

http://products.semelab-tt.com/pdf/A...nNoteAlfet.pdf


Would a powerFET designed solely for high speed switching use and 125W
rating be derated in power handling terms to only 50W say for linear 10 Hz
use. Or secondary oscillation liability if paralleled up devices? or some
other operational failing in audio use not found with smps say ?

** Yawnnnnnnnnnnnnnnn....

More brainless, ****ing TROLLING !!!!!!!

FOAD you vile pommy ****head.



..... Phil


Ah at last , thanks, a pertinent reply to my original question.


** There is no possible answer to a question as wrong headed and stupid as
that.

So you will never get one.

FOAD you vile pommy ****head.




..... Phil

On 05/01/2014 07:53, Jeff Urban wrote:
I wanted to reply to this when you first posted it but I couldn't for
whatever reason. ****ing thing. As you can see I am not posting from
google, which I no longer capitalize !!!! LOL

Anyway, what characterizes ANY part for the transmission of audio is
linearity. Even though the gate of a MOSFET is driven wildly different
than the base of a BPT, linearity of gain fro the very small signal to
the very large signal is the prime. We used to look at the hfe and HFE
gain curves of bipolars in the old days, not it is different.

Any kinds of spurious **** like oscillations would be no good in
switcxhers as well. the thing is, switchers somethimes have a gain curve
that is like, made to be on or off.

An audio transistor must operate in the analog range, that means the
gain curve should be as flat as possible through the operating current
range.

The same is true of a MOSFET.


or on rereading . If an audio application can tolerate a certain amount
of cross-over distortion and general harmonic distortion then there is
no difference in powerfet useage type , up to some power level where
these distortions become too apparent.

On 01/05/2014 03:29 AM, N_Cook wrote:
On 05/01/2014 07:53, Jeff Urban wrote:
I wanted to reply to this when you first posted it but I couldn't for
whatever reason. ****ing thing. As you can see I am not posting from
google, which I no longer capitalize !!!! LOL

Anyway, what characterizes ANY part for the transmission of audio is
linearity. Even though the gate of a MOSFET is driven wildly different
than the base of a BPT, linearity of gain fro the very small signal to
the very large signal is the prime. We used to look at the hfe and HFE
gain curves of bipolars in the old days, not it is different.

Any kinds of spurious **** like oscillations would be no good in
switcxhers as well. the thing is, switchers somethimes have a gain curve
that is like, made to be on or off.

An audio transistor must operate in the analog range, that means the
gain curve should be as flat as possible through the operating current
range.

The same is true of a MOSFET.


or on rereading . If an audio application can tolerate a certain amount
of cross-over distortion and general harmonic distortion then there is
no difference in powerfet useage type , up to some power level where
these distortions become too apparent.

I learned what I needed to know to rebuild a fried Ampeg SVT3Pro. 4 [ea]
irfp9240s 4 [ea] irfp240s. Will oscillate itself to death. Must use a
scope and a light bulb current limiter to detect sudden current surging
due to rf feeding back. I think Vishay has some linear application notes
for these MOSFETs. They can be biased for very tiny crossover notch, but
the spec is bias for 800ma at the AC mains with no signal. Not terribly
efficient. But it's a bass guitar amp.

Shaun wrote:
When I did similar tests, I found the order of magnitude was right,
but the result depended on the shape and volume of the mass of water
and position in the oven. [...]

Wonder what the "official" water configuration is when they determine
the spec?

I don't know about a US Federal Trade Commission (or other agency, or
equivalent in other countries) test procedure; there probably is one but
I don't know it.

I know that older GE microwave ovens, in the little service information
sheet that was folded up inside the oven, gave directions on the test, a
GE part number for a beaker you were supposed to use, and I think a
third-party part number for the thermometer you were supposed to use to
measure the water temperature before and after. I think the water level
was marked on the beaker, and the service sheet said to put it right in
the middle of the oven. You didn't boil it, just heated it for a fixed
amount of time.

If I remember right, the criteria was something like "if the oven
produced between X and Y degrees temperature rise in the water, it's
within spec" - it didn't give you an answer in watts, just an acceptable
temperature range for that particular model oven.

Matt Roberds

"I was
wondering if it was a larger area of silicon so the heat can migrate out
of the die quicker."

That's not the crux of the matter. Power dissipation is power dissipation.
The suitability for audio use is the same as the suitability for any linear use.

Look at the spec sheet carefully, or actually link me to one. Better yet, I got a random one right here :

http://www.classiccmp.org/rtellason/...ata/irf430.pdf

Let that load in another tab for now. Power dissipation is power dissipation. Most of the time it is largely dependent upon the case style but there are other factors. The sheet in the link lists all three in the family at 75 watts.

I would like to see a spec sheet that gives a different Pd for pulsed and linear operation because if it does (not that I have ever seen one), it miust be figured a different way. For example RF power transistors are sometimes rated at their maximum capability in class C operation. This figure is useless to you for audio, or any linear application.

Now on that datasheet, look at figure 3 on the PDF page 4. Looing at the lines and the increments, it is a linear graph, not logarythmic. The lines drawn in the chart indicate the gain of the device. Ideally, those lines would be perfectly straight for linear use, but that is not achievable in real devices.
Even with the line not starting at zero, absolutely straight would be ideal, it doesn't matter where it starts.

As you can see, the line that represents 125C is the straightest, but you can't just run it it at 125C becasue you would have to derate for power dissipation so much that a pair of these 75 watt devices might get you 10 watts or some ridiculous low power like that. It would be very inefficient to say the least, and it would take class A to keep them that hot anyway.

Now, if you look at a MOSFET that is specifically only designed for switching, the "knee" in that curve is likely to be alot more pronounced, and that is a desirable characteristoic for a switcher because the idea is for it to spend as little time as possible in the linear region. No time at all would yield the most efficiency for a switcher. The only dissipation would be the leakage current when turned off times the voltage applied, and the voltage drop across the drain amd source times the current carried. One number of each is very low, therefore the power dissipation is very low at those times.

Then we have the time actually spent between states. That is where the real power dissipation comes in usually. What exacebates the situation is the fact that these devices frequently turn on faster than they turn off. This can cause problems in a totem pole arraingement obviously, or an inductive load as the voltage wants to go go go but the currentis not yet completely shut off off off. Thus the device can be and is frequantly optimized for switching.

This will make it perform very poorly in a linear application. In fact a long time ago I worked on a TV in which someone had replaced a video amplifier with an RF amp transistor that was designed to be a switcher. The result was a picture that had good blacks and whites, but almost no shades of gray, as if it was clipped. However, the actual video level was about right. Do you understand why ?

On a bipolar spec sheet you will find a similar curve but usually it looks upside down sort of from the gain curve on the FET data sheet here. It will have the current gain plotted against collector current. In that case you want the curve to be horizonatally as flat as possible for linear use. For switching, it is a whole different story.

At any rate, minding the divisions on the graph of course, of the three curves there in figure 3, the 125C line is best and the 25C line is worst. You will not get a perfectly straight line, but the closer you come the better.. Ironically the -55C curve is not better, but that is just how these things are.

Now, if you want to parallel fets in a linear application, I can do that, but I need a case of beer. It is not as simple as just using source resistors because for that to work effectively the resistance value would be too high. I have a neat little drive circuit that not only accomplishes the current sharing accurately, but since it effectively shunts drive voltage, eliminates problems with storage time (?), the turning off slower than turning on thing. That can cause alot of problems.

Even in switching circuits, if you are heading for the high frequencies you have to optimize the drive to make sure the damn thing turns off in time. This requires pretty much shorting out the charge on the gate to source capacitance. Driving it linear is not exactly the same, but some of the same principles apply. In more modern devices you don't have to jump through as many hoops. Semiconductor manufacturers do improve their products and lessening drive requirements in all ways is considered an improvement as it is attractive to engineers who have alot to say about which devices are chosen and therefore bought.

This is long enough. I probably will never catch all the typos...