What's the difference between these two output transformer?

[Blair]

As described here: http://www.tubecad.com/2005/March/blog0041.htm

And this:



The big difference I see is that the primaries are also parallel in the first image.

In the bogen, he parallels the outputs and uses the two 16 ohm taps in parallel to make an 8 ohm tap. Does this keep the primary impedance of each transformer the same?

I really want to make sure I am going to be dealing with the primary impedance of 4.5 K as tested on each individual transformer.

Thanks!

Blair

[Blair]

Has anyone ever done either of these configurations? Looking at them with my very limited experience and understanding:

Bogen layout (Bridged)
1) Two separate 100W amps bridged, so the tubes see the same primary impedance as if operating separately.

2) Completely paralleled on primary and secondary. The primary the tubes see is 1/2, or 2.25K, so it would allow for PPP.

Doing it like the dynaco example in the article would make it easier for the driver circuit, but I could never run the amps as stereo which is fine by me.
I could tap in another pair of 8 pin sockets and run EL34s as a six pack to get roughly 150W, or keep my layout and use PPP KT88 into the 2.25K load for 150-200W.

Any benefits or pitfalls to using either output configuration?

Thanks!

Blair