Re: blues junior owners ...
I had a great experience with
Doug's Tubes not too long ago. Doug talked through what I was looking for, then he sent me a variety of 12AX7's and two pairs of EL-84's (
my idea to get a bunch).
For power tubes, I really like the Ei EL-84's. Nice and clear without sounding brittle, and the breakup is gradual. (Better than the original Sovteks, EH or JJ's to my ears.) Avoid the Ei 12AX7s though - bad rep for microphonics. Mine sounded great for 20 minutes, then started making noises.
People are all over the map with 12AX7's - different ears, different amps, and different tubes. The JJ's are too dark for me, but most guys like 'em a lot. The best new preamp tube for cleaner sound in a Blues Jr. might be the latest Shuguang (9th generation Chinese).
I like the new Tung Sols, and Doug sent me two - hot & hotter - schweet!
V1 is the most important tube for tone in the Blues Jr. because it's (most of) the preamp. Changing V2 does almost nothing IME, particularly since only half of it is even used. V3 is the phase inverter - really part of the output section rather than the preamp - but different tubes can change the distortion by driving the output tubes harder (or less).
BTW some vendors sell "balanced" tubes for the phase inverter, but some "experts" like Kevin O'Connor call B.S. on the concept. I simply don't know whose call is correct on this subject
If you check the Blues Jr. Mafia thread over on the Fender Discussion Page, there seem to be a some guys who really like an NOS 5751 in V1, any 12AX7 in V2, and a 12AT7 in V3. The 5751 has slightly less gain than a 12AX7. The 12AT7 has 70% of the gain of a 12AX7 and supposedly a more linear response. That combo does reduce preamp gain and make it cleaner to my ears. Reduced overall volume too, and I
like some preamp distortion... so personally I stick with all 12AX7's.
Others have great experiences with Eurotubes - the emphasis on JJ tubes was too much for me. Your Mileage Will Vary
Sorry I went overboard with this...
Chip