Magnetron replacement,, (substitution)

Electrolytics are often signaificantly over their rated capacity. The difference between 0.9uF and 1.05uf is electrically insignificant.

dave Inscribed thus:

I agree !

If the magnetron is physically the same and the heater voltage is the same then just replace it. It should work ok. You can always do the cup of water test...

HTH.

--
Best Regards: 
                        Baron.

On Saturday, October 12, 2013 10:23:47 PM UTC-4, snipped-for-privacy@gmail.com wro te:

owling last week. We pulled it apart and found that the magnetron had a sho rt between anode and filament. The diode and cap both check good. The cap i s a 1.05uf 2100V unit. I have several new magnetrons in stock meant for com parable GE over the stove units. I don't know what value of cap is used wit h these though. In my travels I have seen caps as low as .90uf. If the GE m ag is the same physical size and mounts the same as the bad Kenmore does wh at would be the harm in using it if the present 1.05uf cap in the Kenmore w ere a different value from what the GE calls for? Thanks for any input. Le nny

I hadn't considered the heater voltage. I guess I figured that they would all be identical. Isn't it generally around two volts? Is there an easy way , or site where I might compare mag. Specs? This tube is real bear to repla ce. The oven was literally built around the magnetron. I would hate to open the filament on the new tube the fist time I fired it up. Lenny

On Saturday, October 12, 2013 10:23:47 PM UTC-4, snipped-for-privacy@gmail.com wro te:

owling last week. We pulled it apart and found that the magnetron had a sho rt between anode and filament. The diode and cap both check good. The cap i s a 1.05uf 2100V unit. I have several new magnetrons in stock meant for com parable GE over the stove units. I don't know what value of cap is used wit h these though. In my travels I have seen caps as low as .90uf. If the GE m ag is the same physical size and mounts the same as the bad Kenmore does wh at would be the harm in using it if the present 1.05uf cap in the Kenmore w ere a different value from what the GE calls for? Thanks for any input. Le nny

"dave"

** Completely irrelevant. ** Not in a microwave oven it ain't.

... Phil

The caps in a microwave HV circuit are oil filled, not electrolytic.

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Interesting. Took some time on Google to find out why. I had wondered why the capacitances were so carefully stated over a very limited range, and why the tolerance was so tight at +/- 3%.

For anyone interested, the answer appears to be here in section 9.5 (assuming it's correct):

By the way, if you want a laugh (and possible pair of future Darwin award winners), have a look at the fourth paragraph of section 8.21!

--

Jeff

You might find some info here:

In the "typical" schematic on page 1, the heater voltage is shown as 3.15v.

--

Jeff

"dave"

** Huh ??

Has this guy never heard of tolerance bands ?

Most film capacitors are rated at 10% tolerance but test much better.

Film caps with 1% tolerance are available and they are darn accurate.

.... Phil

** That explanation is highly simplistic.

A crucial thing with a microwave oven is that the current drawn from the HV transformer is the same on both half cycles of the AC supply - otherwise the iron core saturates and that would blow the AC fuse.

On one half cycle, the transformer charges the film cap and on the next the magnetron draws current from the cap and the transformer in series. There is also series resonance between the cap and the transformer, due to its very high leakage inductance.

Taken together, this explains why microwave ovens are made to suit the local AC supply frequency.

BTW:

If you examine the AC current draw of a microwave oven, it is a pretty good sine wave - remarkable considering what the load inside is like.

... Phil

Wouldn't it make more sense to use a switcher supply now-a-daze? The ovens I've seen had large ergo $$$ transformers.

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"David Lesher"

** Nope.

** Made in China for about $1 or $2 each and normally way outlast the rest of the oven.

Any 1kW SMPS that does the same job is gonna cost 20 times more and be the first thing to fail.

... Phil

On Saturday, October 12, 2013 10:23:47 PM UTC-4, snipped-for-privacy@gmail.com wro te:

owling last week. We pulled it apart and found that the magnetron had a sho rt between anode and filament. The diode and cap both check good. The cap i s a 1.05uf 2100V unit. I have several new magnetrons in stock meant for com parable GE over the stove units. I don't know what value of cap is used wit h these though. In my travels I have seen caps as low as .90uf. If the GE m ag is the same physical size and mounts the same as the bad Kenmore does wh at would be the harm in using it if the present 1.05uf cap in the Kenmore w ere a different value from what the GE calls for? Thanks for any input. Le nny

Thanks for the great explanation of how the oven works Phil. I figured ther e was a resonance factor associated with this but wasn't completely sure. S o then can I surmise that a different cap shifts resonance slightly and the n does that affect maximum power transfer to the load, (Tube)? And then whi le we're at it, it occurred to me that the food must be the tube load, (out put). I'm trying to understand this better so is at least part of that corr ect? Lenny