[R-390] Buck/Boost Transformer

[Barry]

Gang,

I'm curious about wiring a buck/boost transformer.  There are, apparently, at least a couple of 
different ways to do this.

I would have thought this to be the way to do this:

http://johnjeanantiqueradio.com/buck-boost.jpg

However, according to the R390A compendium, there's another way to do this:

http://www.r-390a.net/faq-HiVolt.htm

Are there advantages/disadvantages to one over the other (or are they essentially the same thing)?  
Although I understand (at least on a functional level) how both work, the second one 
seems "backwards" (although I know it isn't).

I assume both require the secondary of the transformer to be able to handle the anticipated load and 
I don't see anything else that would change the requirements on the transformer.

I seem to recall a former list member (Dr. Gerald Johnson) talking about a scheme where the bucking 
transformer only has to be rated in proportion to the amount of voltage it is dropping.  In other 
words, if it's bucking 5 volts from 125, then it only has to be rated at 5/125 of the load.  (That 
wording may not be exactly correct, but I seem to recall the bucking transformer did not have to be 
rated for the full current load).

Am I wrong to assume that the bucking transformer in the above schematics have to handle the full 
load (in amps) or does either one allow the transformer to only be rated at an appropriately smaller 
VA rating (I hope I'm making sense...).

Thanks,
Barry - N4BUQ