mike wrote:
larry moe 'n curly wrote:

mike wrote:

My 27 year old microwave oven was down below 400W output and taking a long
time to heat my coffee.
So, I went out and bought a 1100W one.
Big mistake.
It works fine on coffee, but WAY overcooks small stuff.
Yes, it has a power level setting, but the on-time is 15 seconds
and they modulate the off-time.

Suggestions?

Put in a smaller high voltage capacitor?
Thanks for repeating one of my suggested options.
Can you be a little more theoretical?
One reference suggested that the cap is actually
sized to resonate with the transformer. That would make
the change of cap value much more sensitive than just a power
ratio.
Relevant input?
Thanks, mike

I thought you meant adding another capacitor and switching between it
and the original.

I doubt the capacitor resonates because years ago someone mentioned a
line of microwaves being identical except for power rating, cavity
size, and the size of the high voltage capacitor, which ranged from
about 0.6uF to 1.0uF.

Get an oven with inverter power control, like a Panasonic?
Simple matter of price ;-)

They're not as expensive as some people implied.

larry moe 'n curly wrote:

mike wrote:
larry moe 'n curly wrote:
mike wrote:

My 27 year old microwave oven was down below 400W output and taking a long
time to heat my coffee.
So, I went out and bought a 1100W one.
Big mistake.
It works fine on coffee, but WAY overcooks small stuff.
Yes, it has a power level setting, but the on-time is 15 seconds
and they modulate the off-time.
Suggestions?
Put in a smaller high voltage capacitor?
Thanks for repeating one of my suggested options.
Can you be a little more theoretical?
One reference suggested that the cap is actually
sized to resonate with the transformer. That would make
the change of cap value much more sensitive than just a power
ratio.
Relevant input?
Thanks, mike

I thought you meant adding another capacitor and switching between it
and the original.

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

I doubt the capacitor resonates because years ago someone mentioned a
line of microwaves being identical except for power rating, cavity
size, and the size of the high voltage capacitor, which ranged from
about 0.6uF to 1.0uF.


Get an oven with inverter power control, like a Panasonic?
Simple matter of price ;-)

They're not as expensive as some people implied.
It's all relative. Paid $80 for mine. I did visit a few stores and the
inverter ones seemed to be almost 3x that and they don't go on sale
often. Knowing what I know now, I might have gone with the inverter.
Spilt milk now...

"David Nebenzahl" wrote in message
.com...
On 1/19/2011 12:55 PM mike spake thus:

PeterD wrote:

On Wed, 19 Jan 2011 05:55:03 -0800, "William Sommerwerck"
wrote:

Can you return the oven? You can use the argument that it's
not fit for its intended purpose. Which it isn't.

Nope, my inability to forecast the consequences is not the
fault of the seller.

If your description is correct, the oven is grossly misdesigned.
You do not implement variable power by turning the magenetron on
for 15 seconds, then letting it sit for a minute! I've /never/
seen a microwave oven that works that way. My home GE works fine,
as do all those I've seen where I've worked.

Huh? Virtually all the ones I've seen do just that: run a 10 to 15
second on/off time cycle. The magnetron is turned on with a relay,
so rapid cycling just begs to blow that relay.

It's worse than that. A triac can fix the relay issue. The problem
is the thermal time constant of the magnetron filament.

I guess I'm showing my ignorance here, as I don't know much about
magnetrons, but why can't you just let the filament burn while you cycle
the HV, like you'd do with any other ordinary tube? I mean, with other
tubes, it's OK to apply power to the heater without any anode voltage,
right?


In general, with indirectly heated types, no, it may not be ok. It has been
said that it can lead to cathode poisoning and sometimes cathode stripping.
In the good old days, HT standby switches often used to have a resistor
across them to keep a small bleed current running through the tubes,
however, I must admit that most modern amps that I see have no such
arrangement, so perhaps modern tubes are better at standing up to this sort
of abuse, or else it has become just a forgotten technique? Or maybe, it was
one of those 'myth' things that some manufacturers believed in, but wasn't
actually the case ? Eimac have published booklets about applying voltages in
the correct order and with the correct delays, to their RF Power
transmitting tubes, so I guess that there must be something in it,
somewhere. Are magnetrons indirectly heated ? I had a feeling that I had
seen somewhere that they weren't, and that the modulation introduced by the
AC on the filament, was insignificant compared to the output power at the
frequency of interest, so was ignored.

Arfa

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)


You exceeded the maximum voltage rating of that resistor.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master ...


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

David Nebenzahl wrote:

On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master ...


And yet another snide, useless post from you.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

In article ,
David Nebenzahl wrote:

On 1/19/2011 12:55 PM mike spake thus:

PeterD wrote:

On Wed, 19 Jan 2011 05:55:03 -0800, "William Sommerwerck"
wrote:

Can you return the oven? You can use the argument that it's
not fit for its intended purpose. Which it isn't.

Nope, my inability to forecast the consequences is not the
fault of the seller.

If your description is correct, the oven is grossly misdesigned.
You do not implement variable power by turning the magenetron on
for 15 seconds, then letting it sit for a minute! I've /never/
seen a microwave oven that works that way. My home GE works fine,
as do all those I've seen where I've worked.

Huh? Virtually all the ones I've seen do just that: run a 10 to 15
second on/off time cycle. The magnetron is turned on with a relay,
so rapid cycling just begs to blow that relay.

It's worse than that. A triac can fix the relay issue. The problem
is the thermal time constant of the magnetron filament.

I guess I'm showing my ignorance here, as I don't know much about
magnetrons, but why can't you just let the filament burn while you cycle
the HV, like you'd do with any other ordinary tube? I mean, with other
tubes, it's OK to apply power to the heater without any anode voltage,
right?

Not sure about the ones used in uwave ovens, but with some magnetrons,
once they get going, the filament power has to be reduced (sometimes to
zero) because the filament is heated by the impact of accelerated
electrons banging into it.

Isaac

On Wed, 19 Jan 2011 17:59:29 -0800, David Nebenzahl
wrote:

On 1/19/2011 12:55 PM mike spake thus:

PeterD wrote:

On Wed, 19 Jan 2011 05:55:03 -0800, "William Sommerwerck"
wrote:

Can you return the oven? You can use the argument that it's
not fit for its intended purpose. Which it isn't.

Nope, my inability to forecast the consequences is not the
fault of the seller.

If your description is correct, the oven is grossly misdesigned.
You do not implement variable power by turning the magenetron on
for 15 seconds, then letting it sit for a minute! I've /never/
seen a microwave oven that works that way. My home GE works fine,
as do all those I've seen where I've worked.

Huh? Virtually all the ones I've seen do just that: run a 10 to 15
second on/off time cycle. The magnetron is turned on with a relay,
so rapid cycling just begs to blow that relay.

It's worse than that. A triac can fix the relay issue. The problem
is the thermal time constant of the magnetron filament.

I guess I'm showing my ignorance here, as I don't know much about
magnetrons, but why can't you just let the filament burn while you cycle
the HV, like you'd do with any other ordinary tube? I mean, with other
tubes, it's OK to apply power to the heater without any anode voltage,
right?

The filament is a minor current, the main HV voltage is the issue. To
cycle off the transformer rapidly with a relay would likely result in
a relay lifetime of a few weeks at best.

I don't believe there ever was an issue with the filaments.

I agree, a triac could possibly be used, though you are talking about
swtiching as much as 1500 watts, inductive (because of the
transformer). Might be too expensive to find a triac that will take
that kind of abuse and survive!

On Thu, 20 Jan 2011 21:50:04 -0800, isw wrote:

In article ,
David Nebenzahl wrote:

On 1/19/2011 12:55 PM mike spake thus:

PeterD wrote:

On Wed, 19 Jan 2011 05:55:03 -0800, "William Sommerwerck"
wrote:

Can you return the oven? You can use the argument that it's
not fit for its intended purpose. Which it isn't.

Nope, my inability to forecast the consequences is not the
fault of the seller.

If your description is correct, the oven is grossly misdesigned.
You do not implement variable power by turning the magenetron on
for 15 seconds, then letting it sit for a minute! I've /never/
seen a microwave oven that works that way. My home GE works fine,
as do all those I've seen where I've worked.

Huh? Virtually all the ones I've seen do just that: run a 10 to 15
second on/off time cycle. The magnetron is turned on with a relay,
so rapid cycling just begs to blow that relay.

It's worse than that. A triac can fix the relay issue. The problem
is the thermal time constant of the magnetron filament.

I guess I'm showing my ignorance here, as I don't know much about
magnetrons, but why can't you just let the filament burn while you cycle
the HV, like you'd do with any other ordinary tube? I mean, with other
tubes, it's OK to apply power to the heater without any anode voltage,
right?

Not sure about the ones used in uwave ovens, but with some magnetrons,
once they get going, the filament power has to be reduced (sometimes to
zero) because the filament is heated by the impact of accelerated
electrons banging into it.


Neat trick since the filament emitts teh electrons...

"David Nebenzahl" wrote in message
s.com...
On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master
...



Actually, I think that it is quite a useful comment, as in my experience in
the electronics service business, many techs - particularly modern ones -
have no understanding that a resistor has a maximum working voltage rating,
and have even laughed at the very idea when I have suggested it to them,
until I have shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what Michael
said, and doing just that ...

Arfa

On 1/21/2011 6:02 PM Arfa Daily spake thus:

"David Nebenzahl" wrote in message
s.com...

On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that
can handle that much volts safely...and maybe some means to
make sure that switching a charged cap doesn't explode the
diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to
the cap. I never did find any of the resistor pieces. May have
gotten swept up when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip
master ...

Actually, I think that it is quite a useful comment, as in my experience in
the electronics service business, many techs - particularly modern ones -
have no understanding that a resistor has a maximum working voltage rating,
and have even laughed at the very idea when I have suggested it to them,
until I have shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what Michael
said, and doing just that ...

Well, I have to admit that it (maximum resistor voltage ratings) doesn't
often occur to me, simply because I don't work with HV. But the person
Mr. Terrell responded to above was certainly aware of why his resistor
got blown to smithereens. Hence my annoyance.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

On Sat, 22 Jan 2011 02:02:54 -0000, "Arfa Daily"
wrote:



"David Nebenzahl" wrote in message
rs.com...
On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master
...



Actually, I think that it is quite a useful comment, as in my experience in
the electronics service business, many techs - particularly modern ones -
have no understanding that a resistor has a maximum working voltage rating,
and have even laughed at the very idea when I have suggested it to them,
until I have shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what Michael
said, and doing just that ...

Arfa

Absolutely they do, but I suspect he also exceeded the power rating of
that resistor by a tiny bit as well... g

PeterD wrote:

On Sat, 22 Jan 2011 02:02:54 -0000, "Arfa Daily"
wrote:



"David Nebenzahl" wrote in message
rs.com...
On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master
...



Actually, I think that it is quite a useful comment, as in my experience in
the electronics service business, many techs - particularly modern ones -
have no understanding that a resistor has a maximum working voltage rating,
and have even laughed at the very idea when I have suggested it to them,
until I have shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what Michael
said, and doing just that ...

Absolutely they do, but I suspect he also exceeded the power rating of
that resistor by a tiny bit as well... g


You can exceed the voltage rating, without exceeding the power
rating. Pulse applications can be well below the rated wattage, yet arc
over internally.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

"PeterD" wrote in message
...
On Sat, 22 Jan 2011 02:02:54 -0000, "Arfa Daily"
wrote:



"David Nebenzahl" wrote in message
ers.com...
On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that can
handle that much volts safely...and maybe some means to make sure
that switching a charged cap doesn't explode the diode or the switch.

Some months ago, I had to replace the diode in my old one.
Hooked a resistor to a couple of clip leads and hooked them to the
cap.
I never did find any of the resistor pieces. May have gotten swept up
when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip master
...



Actually, I think that it is quite a useful comment, as in my experience
in
the electronics service business, many techs - particularly modern ones -
have no understanding that a resistor has a maximum working voltage
rating,
and have even laughed at the very idea when I have suggested it to them,
until I have shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what Michael
said, and doing just that ...

Arfa

Absolutely they do, but I suspect he also exceeded the power rating of
that resistor by a tiny bit as well... g

Well yeah. That too, I agree ! :-)

Arfa

"David Nebenzahl" wrote in message
s.com...
On 1/21/2011 6:02 PM Arfa Daily spake thus:

"David Nebenzahl" wrote in message
s.com...

On 1/20/2011 4:44 AM Michael A. Terrell spake thus:

mike wrote:

Yes, that's what I had in mind. All you need is a switch that
can handle that much volts safely...and maybe some means to
make sure that switching a charged cap doesn't explode the
diode or the switch.

Some months ago, I had to replace the diode in my old one. Hooked a
resistor to a couple of clip leads and hooked them to
the cap. I never did find any of the resistor pieces. May have
gotten swept up when I cleaned up the puddle I made. ;-)

You exceeded the maximum voltage rating of that resistor.

Gee, ya think?

Another incredibly useful 1-line post from the shoot-from-the-hip
master ...

Actually, I think that it is quite a useful comment, as in my experience
in the electronics service business, many techs - particularly modern
ones - have no understanding that a resistor has a maximum working
voltage rating, and have even laughed at the very idea when I have
suggested it to them, until I have shown them in a component catalogue.
I'm willing to bet that prior to this exchange, there were more than a
few reading what Michael said, and doing just that ...

Well, I have to admit that it (maximum resistor voltage ratings) doesn't
often occur to me, simply because I don't work with HV. But the person Mr.
Terrell responded to above was certainly aware of why his resistor got
blown to smithereens. Hence my annoyance.



I see that, but some other less experienced people reading the thread, may
well have learnt something from the comment. Still, all sorted now, and
everyone's up to speed on resistor voltage ratings !

Arfa

On 1/22/2011 7:56 AM Arfa Daily spake thus:

"David Nebenzahl" wrote in message
s.com...

On 1/21/2011 6:02 PM Arfa Daily spake thus:

Actually, I think that it is quite a useful comment, as in my
experience in the electronics service business, many techs -
particularly modern ones - have no understanding that a resistor
has a maximum working voltage rating, and have even laughed at
the very idea when I have suggested it to them, until I have
shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what
Michael said, and doing just that ...

Well, I have to admit that it (maximum resistor voltage ratings)
doesn't often occur to me, simply because I don't work with HV. But
the person Mr. Terrell responded to above was certainly aware of
why his resistor got blown to smithereens. Hence my annoyance.

I see that, but some other less experienced people reading the thread, may
well have learnt something from the comment. Still, all sorted now, and
everyone's up to speed on resistor voltage ratings !

Well, point taken.

While we're on the subject, where would one get HV resistors, anyhow?
Any US suppliers?


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

"David Nebenzahl" wrote in message
.com...
On 1/22/2011 7:56 AM Arfa Daily spake thus:

"David Nebenzahl" wrote in message
s.com...

On 1/21/2011 6:02 PM Arfa Daily spake thus:

Actually, I think that it is quite a useful comment, as in my
experience in the electronics service business, many techs -
particularly modern ones - have no understanding that a resistor
has a maximum working voltage rating, and have even laughed at
the very idea when I have suggested it to them, until I have
shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what
Michael said, and doing just that ...

Well, I have to admit that it (maximum resistor voltage ratings)
doesn't often occur to me, simply because I don't work with HV. But
the person Mr. Terrell responded to above was certainly aware of
why his resistor got blown to smithereens. Hence my annoyance.

I see that, but some other less experienced people reading the thread,
may well have learnt something from the comment. Still, all sorted now,
and everyone's up to speed on resistor voltage ratings !

Well, point taken.

While we're on the subject, where would one get HV resistors, anyhow? Any
US suppliers?


--

I haven't seen any *very* high voltage resistors for some time now in
catalogues, although I expect if you went looking for them, they are still
around from specialist manufacturers. Most that are readily available here
in the UK are rated at up to 400v for some, rather less for others. If I am
replacing a resistor that is going to have a lot of volts across it - for
instance a bleed or voltage sharing resistor across a high voltage cap in a
tube amplifier - I tend to make one up from two half-value resistors in
series. Likewise, when replacing some anode load resistors in 12AX7 or
whatever stages, as these are often 100k connected to a rail of up to 400v,
with the actual anode voltage at the other end, two or even three hundred
volts lower than that. Two 47k resistors rated at 250v each, and connected
in series, ensure that the replacement is up to the job, long term.

Arfa

David Nebenzahl wrote:

On 1/22/2011 7:56 AM Arfa Daily spake thus:

"David Nebenzahl" wrote in message
s.com...

On 1/21/2011 6:02 PM Arfa Daily spake thus:

Actually, I think that it is quite a useful comment, as in my
experience in the electronics service business, many techs -
particularly modern ones - have no understanding that a resistor
has a maximum working voltage rating, and have even laughed at
the very idea when I have suggested it to them, until I have
shown them in a component catalogue. I'm willing to bet that
prior to this exchange, there were more than a few reading what
Michael said, and doing just that ...

Well, I have to admit that it (maximum resistor voltage ratings)
doesn't often occur to me, simply because I don't work with HV. But
the person Mr. Terrell responded to above was certainly aware of
why his resistor got blown to smithereens. Hence my annoyance.

I see that, but some other less experienced people reading the thread, may
well have learnt something from the comment. Still, all sorted now, and
everyone's up to speed on resistor voltage ratings !

Well, point taken.

While we're on the subject, where would one get HV resistors, anyhow?
Any US suppliers?


http://www.caddock.com/
http://www.ohmite.com/cgi-bin/products.cgi
http://www.ohmcraft.com/resistors/

http://www2.eem.com/ is a database of electronics manufacturers where
you should find more. Several brands I used to use are no longer in
busines or at least under their original names.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.