Blown mains fuse, cracked through the ceramic and sand and blackened
internal surface. Someone had replaced the 1A HT fuse with 3.1A at some
point, which was ok. Someone had managed to strip the internal
"screening" card from the staples holding it the cab base. Metal side to
the inside, only the vaguest of plastic sheet insulation over it and
could have been touching anything. No tag for an earth point/wire that I
can see anyway, so that will not be going back inside. All logo/printing
of each valve looks balanced thermal degradation (slight) but these
Electro Harmonix all dated 0611 have flattened domes at the getter end.
There is a recessed rough dimple in each of these , all
off centre so unlikely at manufacture, signs of overheating? I,ve not
seen these rather raggedy dimples before but I cannot believe the
dimples would be so remarkably similar if the flat part of the tube was
heated enough to start collapsing inwards (valves with base at bottom ,
ie not inverted orientation in use). Valve bases look normal, no
colourations or discoloured valve Rs inside etc .
No EL34 tested yet but the first valve I remove, the forked contact for
grid pin 5 takes a 2.5mm drill shank inserted but touches a 2.55mm one.
Previous Hiwatt, different model, stopped bouncing back after I replaced
all the p5 forks with proper 30 yearold NOS ones . That one had forks
with about 2.2/2.3mm forks that were suspect. That Hiwatt had wired in
sockets but this is pcb type, so how to remove individual pins without
removing whole sockets? Replacing complete 2007 sockets with 2013 ones
seems a hiding to nothing. For good measure RoHS/PbF stickers aplenty.
Owner queries whether it is due to being borrowed by a wannabe bass
guitarist who uses extra mass per unit length strings on ordinary
electric guitar, for some musical style purpose.

Replace the fuse and the amp works fine, which doesn't help of course.
The insertion / pull force of the EL34s is far too low, from experience,
what force in KN that is I don't know

Extraction only fingers of one hand , no wiggling required. Insertion
force 3 to 4Kg far lower than usual. C frame around and under amp
connected to a spring balance and a block of expanded polystyrene , off
amp deformed with impressions to take top of C and top of valve.
All 8 laminations bolts for the 2 Tx are loose to the point of nuts soon
to be dropping off for 2 of the mains TX bolts.
One of the seriously cruddy output fuses, with LED indicators, has
highly suspect contact where the end cap quarter-turns in, so yet again
having to replace these pcb mount fuse holders

Looks like a matter of desoldering the heater chain wires and then hot
air gun to the pcb under each socket while pulling the socket , to
remove them.
Seems odd to have a fuse in the AC to the bias supply

Next time I have to desolder double sided large-mass PbF soldered valve
bases , I will attack as the only time I've done lead-pipe soldering and
use 2 hot air guns, one heating the base and one on the other usual side
of the pcb.
These white no name porcelain bases have a form of pin I've not seen
before. If you view into the holes that take the valve pins , you can
see the pins have joggles to them in a circumferential sense. Not the
fairly common pip joggle inwards towards the valve pin at the point of
contact but off the flat face of the pin , like mini humps. What that
means is that instead of the valve pin forcing the forks apart, the 2
parts of the fork can slightly rotate out of diametrical alignment and
so just a touching contact, not full mechanical contact
I think the pin material is thick enough and the forks are not splaying
apart , the usual dodgey contact failure mechanism but a slight
torsional twist instead. Perhaps removal of p5 at least and squashing
out the 2 humps is all that is required.
The flimsy no name pcb 20mm fuseholders have a type number
PTF
50
on them

These joggled pins would probably have worked if the slots in the
ceramic bases were a mm thinner so the metal forks could not twist/splay
along their length. So an in-situ workaround would probably be formed
metal forks pushed into the p2,5,7 slots to close up the freedom to move