I would use tubes from the same batch, but matching isn't really
necessary. Keep in mind the tubes are only matched for a
short time, because as they age, they go their own ways.
Thanks Tom , that's good news , I'm following a few sets of EL84 on ebay . There are lots of NOS tubes from Russian army surplus ( usually same production date batches , though not matched ) at very low price ( around $25 a quad) . I'll give 'em a try and let you guys know how they perform .
Cheers.
Suso .