What does TWEED POWER technically do?

[cho]

It would seem the MKIII's may not have had a tweed option.
I'm not that familiar with their options.

This thread seems to think the Simul-Sat's were based on a IVa.
I'll pull my IVa chassis one of these days and see, but the innards of my Simul-Sat look a lot like a MKIII to me...

http://forum.grailtone.com/viewtopic.php?f=3&t=27803&p=205695&hilit=+mark+III+tweed#p205695

Perhaps it is that the Simul Sat has the preamp board from a MIII, but the transformers of a MIV. Can anyone verify this looking at transformer serial #'s?