Those SV83's are the ones I tried out at first, but they're not that good.
[cheap though]. I bought a batch of Svetlana's here on the forum; the ones with the big logo, and they sound a lot better.
I also prefer the sound of the SV83 over the EL84's ; more speed and neutral sounding in my install.
Great amp you've got, now find the perfect match of tubes that suit your install and you'll stop looking for something else...

Nico