Circuit Symbol

Gentlemen,

A chum of mine who's into classic cars has asked me to take a look at
the radio out of his 1938 Bentley which has never worked in all the
years he's had it in his ownership. Obviously, given the year, this is
an all-valve job (if you're in the US, I'm referring to what YOU call
"tubes"). There isn't a single semiconductor in this thing cos they
weren't invented until much later. The valves require an anode
("plate" if you're in the US) voltage of 235V so there's a DC to DC
up-converter to generate that from the 12V battery. Rather interesting
approach they've used and one can see an embryonic SMPS in there!
Anyway, there's a schematic symbol I can't identify for sure. Could be
a fuse, could be a link or jumper, could be a current test point, I've
no idea. So can some kind, intelligent soul enlighten me? They're
labeled V1 through V8. Here's a pic:

https://disk.yandex.com/i/mIv_txLia6Xx4Q

TIA,
CD