Re: EL84 v.s. El34 - TONAL differences
The EL34 and EL84 tonal differences are irrelevant. They aren't interchangeable.
Wait!.
In some amps, this isn't true.
VHT has several amps that allow you to throw the most common power tubes (EL84, 6V6GT, 6L6, EL34, KT66, ...).
So... differences are relevant... sometimes.
To me, they are somewhat similar, or at least closer one to the other than any of those compared to the "american way" (6V6GT, 6L6).
Compared to those, they have less boomy or big low end, more prominent mids or mid-highs and a direct cut-the-mix sound. They naturally put your guitar on the mix.
Differences are bigger, the hotter you run both tubes.
The EL34 has some bite (attack) more explosive than the EL84 and its harmonics are more complex and 3D-like.
I love the crunchy-warm EL84 in Class A design and, EL34 delivering big stadium rock in Class A/B design.
Said this. Everything makes no sense by itself.
Amp design is key. Tubes you choose for pre-amp, power amp and rectifier (if a tube one) make a big difference.
Tube brand/model behave very differently.
Speakers and cabs make a huge difference...
Usually each amp designed for a certain tube, will sound awesome if you find the right brand/model.
At the end, it's all about which power do you really need and, how you can crank the tubes (were they deliver their own spice).
Running those tubes cold, will sound very close (bored, lifeless) so, go for the power you can hold.