Fred McKenzie wrote:
In article ,
mike wrote:

Yes, it has a power level setting, but the on-time is 15 seconds
and they modulate the off-time.
I tried to heat a frozen hamburger patty. It boils the liquid around
the outside for 15 seconds, but the inside is still frozen.

Mike-

Does the new microwave have a Defrost option? If so, does it also cook
for 15 seconds at full power?

I had a small microwave back in the 70s that had a low power setting.
My memory is a little hazy, but I think the low power setting switched a
capacitor in series with the high voltage transformer primary. It acted
as a ballast to reduce magnetron voltage.

Fred
Well, that's what I was asking about.
I don't think there's anything you can do in the primary circuit.
The magnetron filament runs off the same transformer as the high voltage.
If you reduce the average input, you also reduce the average filament
voltage/temperature.
There are two basic issues that I can think of.
1) It takes time for the filament to come up to temperature.
2) The more you thermal-cycle the filament, the shorter the life.
The 15-seconds is a compromise that mostly works.

If you want to pulse the anode, you have to have a separate transformer for
the filament to keep it up to temperature while you pulse the anode.
Conceptually trivial, but it adds to the cost.

As I mentioned in the original posting, you probably can change the value
of the secondary cap, but that takes a high-voltage switch.
I'm interested to learn if anybody's done that. Or if there's
any theoretical basis for concluding that it's a bad idea.