I emailed Nik and here are his answers if anyone is curious:

My Questions:
1. Which year has the tightest Bass response?
The bass response is about same, but the '67 would probably have most,
with the shared cathode, and more bass-like circuit.

2. Which year has the most Gain
'72 would, with the 100K/4ohm NFB setup, and the preamp

3. Which year has the most headroom?
About same, except perhaps the '72

4. Do they all have the same size Transformers?
Yes, we use the same trannies on them

5. Which year is the brightest sounding?
Bright wise, doesn't matter - see the layouts. We have put bright switch on
this, so you can choose whether to have the bright cap or not.

But, if selected, the 72 would be it, as it selects 4700pf cap, the biggest
amongst all these.

The trick is, not to use the Marshall while setting Vol pot (bright) low -
it'd be bright sounding

As you turn up the pot, the bright caps gradually get defeated, but still
maintaining focus and gain.


Nik is really quick & thorough with answering my (endless) questions. I really don't know anything about electronics so this was REALLLLY helpful.