Di talaga magkakasya yan spanky. Parang EL84 ata yang sinasaksak nya. Dapat try nya 12ax7 lang
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Seriously now...I do think it's possible but I failed when I tried to squeeze in a 12ax7 tube into my TS7. Pwede pa din but it will entail
a. Not using a tube socket (major bugger)
b. cutting the tube leads then
c. Directly soldering the components to the tube leads. Or maybe not, there could be some other construction permutation.
There came out whats known as subminiature (pencil) tubes, small enough to be directly soldered into a circuitboard and inserted into a pedal. They're rare, but can be had.