[Amps] Microwave Oven Power Transformer

[Manfred Mornhinweg]

I can very well understand the temptation to use MOTs, since they are so 
widely available for free, and let's face it, most of us are cheapskates!

But please do understand what MOTs are:

They are the absolutely cheapest possible implementation of a 
current-regulating transformer, designed to work always at fixed full 
power, for a few minutes at a time, in the airstream of a fan.

And for a ham linear amplifier you want:

- NOT a current regulating transformer, but one that is the exact 
opposite: As stable a voltage as possible.

- A transformer that idles very well, since typically at least 80% of 
the time a ham amp transformer will be idling.

- A transformer that can stay energized for the 48 hours of a contest 
weekend, or the two weeks of a DXpedition.

So the requierements for a ham amp transformer are diametrally opposed 
to those for a MOT, and it's just not very convenient to adapt MOTs for 
ham amplifier use. Better use purpose made transformers for ham amps, 
and leave the free surplus MOTs for other hobby applications to which 
they are better suited, such as small spot welders to weld those battery 
tabs, light effect setups using gas discharge tubes, Jacob's ladders to 
scare away your mother-in-law, and the like.

It's perfectly possible to recover just the core of a MOT and rewind it 
as a normal transformer with good efficiency, but this requires throwing 
away the wire, which is the expensive part, to recover the iron, which 
is rather inexpensive, and then do all the winding work. On top of that 
many MOTs have the cores welded together, so they are damaged when taken 
apart. And a 1500 watt MOT will only make roughly a 200 watt, normally 
efficient transformer!

This is basically an option for people who can't buy transformer 
laminations new. If you can buy them new, better do that, because the 
laminations contained in a MOT would be worth only about 3 dollars! And 
from a scrap yard, less than one dollar...

Manfred


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