Just listened to some 72 shows while on a long drive (4/26 Lovelight…OMFG!!! I forgot how good that was!
) and my thought is that you are hearing the power tubes starting to distort here. This is the end of the era where he uses the full Twin Reverbs before they went to the pre-amp out and the original pre-Budman MacIntosh’s around late 72, early 73. IMHO Jerry’s tone trended down from here, although the tb500 era tones are pretty good too, and I think it’s because he lost the power section saturation when they went to the pre-amp outs.
You won’t get this sound from dirt pedals or hitting pre-amp triode tubes hard. The best way to get this sound is going to be to really drive a pair or quad of 6L6’s and then figure out how to tame the volume.
I think a reactive load attenuator or load box is the way to go here. Push the amp, get the tubes cookin’ and then absorb the excessive (for home) power in the load box and re-amp it with a clean SS amp into one or more JBL’s. The chain will be somewhat similar to the popular pre-amp setups and Jerry’s post 72 rigs, but when you include the phase inverter, power tubes and output transformer in the chain the sound is different, more saturated and less clean than later Jerry. That setup will get you Europe 72 with a Strat and the late 60’s through 71 tones (mostly) with Les Pauls with p90’s or an SG with hums. Turn down to keep it clean and you will be pretty close to the later rig tones as well.