Dead amp. It never looks right,to me, to use 1/3W anode dropper
resistors, even if high voltage type. Did Marshall stop using HV types,
these are light green body if suggestive of anything?
100K open circuit one to V2p2. 2x seriesed 47K 0.5W will go back in
there and its mate.
No discolouration to the coating, scraped back coating and normal under
the axial sampling I scraped off ,dark grey MO spiral, failed at one
end. To last but 2 turn measured 63K, to last turn before end measured
110K. Presumably failure by gradual oxide breakdown by micro-arcing and
thinning and resistance increase.
Another problem waiting to happen, especially if rough handled/knocked
on front. There is a sub-front panel in these , rivetted to the pcb.
Unnecessarily long landing tongues protrude across the pcb and their
edges are about 1mm average gap to component leads, gap to one resistor
about half a mm.