Jimmy Page 1973 MSG Marshall modifications

[tzurby]

I know, this has been discussed thousands of times (Jimmy Page’s sound on the 1973 Madison Square Garden [MSG] concert, filmed for the 1976 film The Song Remains the Same), but I did not find the conclusion regarding his Marshall amp and possible modifications. Maybe it is hidden somewhere in this forum. I cannot find it.
This post is an attempt to solve this mystery.


What we know:
1. The pickups play an important part. For the Les Paul (according to Bryan Williams https://www.youtube.com/watch?v=zFY5daT_s6E): “hot PAF on the neck 8.2-8.6K alnico 2 or unorientated alnico 5 magnets and a 70's T-Top around 7.5-7.6K”. Pages mainly plays in the middle position and the tone always is crisp, never muddy. But the basic sound characteristics can also be obtained with an early 70s Gibson SG (or EDS-1275) with stock T-Tops in both positions.
2. Echoplex EP-3 as a preamp.

The sound is very present and bright (but not harsh), the JP “chirp”, not much bass, there is lots of sustain and the tone is very dynamic. Playing lightly (and turning down the volume pots) gives a clean and clear, ringing tone, turning the volume to 10 gives lots of distortion. (As far as I know, Page never changed the settings on his Marshall during the concert.)

Page used a Super Bass (year unknown, but a Plexi) as his main amp. It was modified by Tony Franks https://www.marshallforum.com/threads/j ... ss.108279/(sometimes one reads Tony Frank). However, the broad consensus is that the KT88 modification (also by Franks) came later. http://forum.metropoulos.net/viewtopic.php?t=38465

So, what did Franks do in order to achieve that sound? What would a qualified amp technician do when a guitarist asks him (I am guessing): “Hey Mr. Franks, I need a clearer tone, lots of dynamics, and more distortion when running on 10 on my guitar.”

Why did Page (or Franks) choose a Super Bass? Don’t they give the oppositive of a clear distorted tone, a “woofy” tone, as Guitar Amp Tech Chris from Sydney puts it? https://youtu.be/rBq4q5ZqeTk?t=727 (Here is an article praising the Super Bass. https://guitar.com/review/vintage-revie ... uper-bass/)

The only suggestion for this “mysterious mod” that I found is “an internal jumper between the channels”. https://www.lespaulforum.com/index.php? ... nk.109458/Could it be just that?

Will a 50 Watt Plexi (I have one) give enough headroom to achieve that sound?