I always thought the EMT-240 was a step up from the 140.
It was an attempt to turn the 140 into something more portable and less finicky.
The 140 has its issues and needs finessing...and don't ever open the sucker up and mess with the tension.
That's why finding one that is not complete or working is often a headache.
Now the 240 has its own "don't touch" thing. You can open up the outer case and look inside...man, wear a gas mask, 'cuz the adhesives they used to attach dampening material on the inner walls...ARE FRIGGIN SO NASTY...you will not be able to get the smell out of your nose or your room for days!!!
I opened mine up to check it out (luckily not at my place initially)...and WOW!!! what a stink.
When I got it home, I opened it up in my outer foyer, with the screen doors wide open, and I wore a heavy-duty mask, meant for toxic fumes.
Back to the guts...
Inside are the electronics and the springs that hold the inner tank, which houses the actual gold foil plate.
That inner tank you never want to open, if you don't have to...and that too has a tension on that foil that you don't want to mess with.
I did have to re-tension the heavy springs that hold the inner tank suspended in mid air, as it was sagging a bit on the bottom from years, and years of just sitting, as the inner tank is not light, to say the least.
So it was a good thing I opened it (even with the nasty stink) 'cuz I was hearing a resonance if I gave the outer case a light bump, and it was because the tank was j-u-s-t rubbing at the bottom.
Ended up being an easy fix to realign it and tighten up the springs on top and sides...so it should be good to go for another 20-30 years.
So I guess there was some desire to replicate the 140 plate in a smaller size and using gold foil instead of an actual metal plate (though they are not very thick either)...but they never got the sound of the LARGE 140 plate on a gold foil plate that is about 12" x 12".
Still the 240 has its sound...and it's particularly sweet on drums at a couple of the shorter settings.
There...now you know even more than you wanted to.