A few Marvin's on the Black guitar site I've played and are owned by a friend of mine.
The ones you see with the Burns amp as a stand, are guitars owned by Alfons a famous Burns collector form The Netherlands.
One of his Marvin's is the 6026 first owned by a other friend of mine, who's pictured with his band in the Burns1979 book.
The band had all Burns 3 Marvin's and the second Shadow bass ever made (the first production model).
Those guitars were all sold early 70's , ten years later Nico Nelson(yes Lord Nelson relative)bought the 6026 to satisfied his longing to the past.
Sadly past away but the stories he told us about to be the first band after the shads to get the Burns,staying with us.
Funny to see a Marvin just 9 digits later has a pickguard date of January and mine is March...so what I've many times wrote in the past, about the all over the place manufacturing process of Burns is proved again...
I have a Marvin of every Burns production period and I noticed it too about the tubes, but never mentioned it again after I wrote about it... after the 2005 Custom Shadows guards red Marvin was launched....I got slaughtered on the net
Cheers Rob