Weir used 2 different Boogies pretty consistently from 75'-late 78'...
He had a 75' Mark I Combo which is 1 of 6 The Dead purchased from Boogie in and around the Blues for Allah sessions. He used this almost exclusively as a live rig with a McIntosh MC2300 from 75' to 12/31/76. Weir, Garcia and Godchaux all used them for the 76' comeback tour. As an interesting sidenote it looks as if Boogie sent them a few with 5 band EQ...Some 76' gigs have either Garcia and/or Weir using the model with the GEQ. It changes show to show in some cases. Some nights none of the ones with GEQ are used.
When the Dead went out on the road in early 77' Weir received a new Mark I Head with reverb & 5-band EQ which Boogie confirms is actually a 76' production model. It is virtually an identical amp circuit-wise to the 75' Boogie combos...but Boogie was constantly tweaking the Mark I circuit path during those years, particularly the pre-amp. You can line 10 Mark I's up in a row from that era and they all sound slightly different. Weir uses this amp exclusively for some time. Although both Peavey & Music Man amps make appearances, the Boogie continues to show up in late 1978 with both The Dead and The Bob Weir Band...
Boogie Mark I's have shot up in price over the last several years...rightfully so in my humble opinion. They can still be had for about $1000 if you dig. The asking price recently has been more like $1500-$4500 depending on features, hardwood/cane, reverb, EQ, year produced, etc...
"It all rolls into one..."