I need some new EL84's for my Classic 30. The local shop has some Mesa EL84's for a reasonable price. Thing is, they come in pairs and I need 4. Is there a problem with buying 2 pair and putting them in instead of a matched quad?
If they have the same plate current or number on them then they should be fine. Order from eurotubes.com or tubestore.com and get a quad for most likely cheaper
If you have two matched pairs, you should be able to put one tube from each pair on each "side" of the output transformer and be fine. IOW take pair #1 and put one in V4 and the other in V7. Put pair #2 in V5 & V6. That's assuming this schematic is correct.
FWIW Mesa EL-84s were some of my least favorites in a Blues Jr. Sounded muddy and had a somewhat harsh breakup. EH, JJ, and especially Ei EL-84s were much nicer to my ears. Shop online at http://thetubestore.com/ or http://www.dougstubes.com/index.html unless you want JJs - then go to EuroTubes for a better price.
Take a look at the color code for the mesas. If the two pairs are the same color it's a matched quad. Then again the sales guy should have known that too.