RR-4D!

[cadman]

Hey Guys,

Check it out, an RR-4D with owner's manual, rescued from sitting in the shop area of an appliance store for the last couple years. Works beautifully too, though I question whether or not it leaks (headache causer?). The door seal looks nice and soft and the door closes exceptionally well.

This is still an electro-magnet model and is heavy beyond belief. AFAIK, the 4D is the first defrosting model. Slide the chrome plated lever over for auto-defrost and you can hear it mechanically turn the magnetron on and off as it cycles.

Check the link too for a clip of the buzzer. Wow that's abrasive : )

http://www.eldocountry.com/radarange/buzz.mp3

 

[cadman]

And the icing....

 

[westytoploader]

Cool Radarange!

The buzzing sounds more like my Kenmore dryer's end-of-cycle signal than anything on a microwave!

 

[swestoyz]

Oh Yeah!

It is so nice to see that unit in your kitchen than @ Smitty's. What a find my friend!

 

[partscounterman]

That awful buzzer

I had pretty much the same model once and thank goodness there was a small switch at the bottom of the control panel to turn that wretched thing OFF.

 

[kenmore1978]

magnetron

So what's the difference the electromagnet models and the current stuff?

 

[cadman]

Electromagnets....

The difference? About 25 pounds : )

Actually, I'm not entirely certain but from what I understand, a magnetic field is required to set up a 'spin' on the electrons being shot from the magnetron (that's how you get molecular movement in what you're cooking). I don't understand why permanent magnets weren't used in the early models since I doubt the Amana engineers completely glossed over them. What I do know is that there is a LARGE transformer in the right hand side behind the control panel that is not there in the later models. My hunch is this is the power source for the electromagnets, though I'd like to see a schematic to confirm. Either way, a giant iron-core transformer adds some significant weight to the other transformers and various "industrial" parts that make these such well-built machines.

Cory

 

[tolivac]

Magnetron

Yes-a strong magnetic feild is required for the magnetron tube to work-The ancesters of the tubes in your microwave oven are those used in radar transmitters.They are still used today.These have perm magnets.The early magnetrons in microwave cookers did use an electromagnet for the feild-why I don't know-perm mag magnetrons were available for the oven builders to use.In some microwave ovens-a separate transformer was used to generate the HV for the magnetron CATHODE and another for the filament.In manetrons wether it be microwave cookers or radar transmitters-the cathode of the tube is fed with negative HV-the positive pole of the HV supply is grounded to the chassis.In both ovens and radar sets-the tube body is then grounded for operator safety-and no need to insulate the waveguide from the tube to isolate the HV.I used to have a service book on early microwave ovens-a friend borrowed it to fix his and forgot to return it.Was an interesting book.Even had service instructions for the very early liquid cooled magnetron tube ovens.Had a closed system .

 

[tolivac]

Manetron#2

The Magnetron tube is an interesting device-You put HV DC into it and LV AC into the filament-and from the waveguide connector on the magnetron--you get the microwave energy.Its a self contained oscillator-no other devices required.So far no solid state device is available to replace it.In some radar transm itters they had "tuneable" magnetrons-The sizes of the cavities could be varied-changing the output frequency.In microwave ovens its a fixed frequency Magnetron(2.4Ghz)The anode block of the tube has cavities cut into it that resonate at the output frequency when the rotating electron beam strikes them-the energy is collected by a probe and then radiated out of the magnetron's output connector.(waveguide)Those tuneable magnetron tubes are VERY expensive!!I used to have a surplus one.The mechanism was pretty interesting.Got lost in a flood.

 

[cadman]

Tolivac, thanks for that informative and concise explanation, it makes perfect sense to me now. I dabble in vac tube electronics so all of that hits close to home but have never done much tinkering on the Radars'. They usually never need it : )

Cory

 

[tolivac]

Radar equipment

Cory:
glad it was some help-I thought back and hear the legends that the "microwave oven" was built up from old radar parts and another rumer of a radar service engineer cooking a hot dog on a stick in front of a radar dish-This would be VERY dangerous!! Radar transmitters generate up to a 1000 times more power than your microwave cooker.I know of someone who worked on radar transmitters when he worked in the Navy and Coast Guard.Some of the stories he could tell were interesting and even frightening!!Radar transmitter magnetrons are pulsed with a circuit called the "pulse Modulator"This contains a thyratron tube(gas filled triode)that generates the HV DC pulse to the magnetron cathode to generate the radar signal.I your microwave oven-the tube is "pulse" in a way by a voltage doubler circuit connected to the HV secondary of the oven's power transformer-the other sec winding lights the filament of the magnetron tube.The filament widning of the transformer has to be heavily insulated electrically to withstand the high voltage fed to the magnetron tube fil-cathode(its a directly heated tube-no cathode cylinder like in small tubes)The voltage doubler circcuit couple diodes and small capacitros and a large cap-can even be built into the cathode end of the magnetron.The larger cap is separate though.It can store a lethal charge.The DC pulse voltage is anywhere from 1200-2800V.One time I had an old microwave oven tube and pulse it with only 100V-and it was enough to flash a neon bulb held close to the magnetrons output coupler.Think magnetrons are fascinating devices.-but dangerous in some instances.