If you own an Oriental/Kumata ATSF E1 A/B set with the original dummy B unit (the first run)...
(
http://www.spookshow.net/loco/kumatae.html )
or you are just a brass collector that likes to collect everything....
There is a very rare piece on ebay right now.
It is the B unit power chassis in it's original box. After watching ebay for years, this is only the second one I've ever seen still in the box.
When oriental came out with the E1 set, it was a bit anaemic with only the powered A unit. So Kumata went back and released a powered chassis for dummy B unit owners (the second run had A and B powered.
Of course I have no connection to this auction. I just know a lot about Kumata brass.
If you have a dummy B unit, I would think you might be interested in this.
http://www.ebay.com/itm/KMT-N-Scale-E-Unit-Power-Chassis-/302428982450And of course, if you have a trashed B unit to the E3/6, this would power that too as a replacement.