Differences between the various "types" of EL-84´s you can disregard.
Some of them were developed for higher B+ voltages but history has proven to us that basically any EL-84 out there will surpass what datasheet tells,and then some.
It´s cousin,the PL-84,has been hit with 700 volts to no ills in for instance the Hohner Duo 1200.
If you want to be on the safe side at all times try finding a matched pair of russian made 6n14p. They´re one of the sturdies 84 type tubes out there and should be reasonably cheap if you pick them up on for instance Ucrainian e-bay.
Same goes for ECC-83.
The various nomers of tubes,in general,are really nothing but specifications. Ie;tubes that do not meet datasheet specs are..not tube of the given designation. So. If an ECC-83 is an ECC-83s amount from slim to none as far as differences them between.
In short?
Install any damn 83 you fancy and be done with it.
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