I think the best GP tubes are the ElectroHarmonix.
The ElectroHarmonix 12AX7EHs are a good choice for an under 9.00/each tube. The have lots of definition (both highs and lows) for about any amp.
I find that most of the Sovtek preamp tubes are too dark sounding (for me), and the JJs, while great highs and lows, can suffer from unusable microphonics (high pitch whines and static sounds). I have hundreds of preamp tubes, and find myself buying the 12AX7EHs or high-end NOS tubes every time rather than use my 'other brands' I stock for repairs, replacements, and new builds (my stocks include JJ tesla, GrooveTube, Ei, Tungsram, Sovtek, and even Chino).
Now, 99 people may disagree with my love of the EH tubes, but I base that on my own observation, and having to re-replace tubes due to microphonics, 'wrong' sound, and price. I have not had an amp come back for re-warranty work that was tubed with ElectroHarmonix tubes (I hope that means they worked for the buyers! :doh: ).
I really like the Sovtek line as my 'gotta get it right first without testing' line of tubes. The EH tubes are slowly getting to be my first referral tube line, but right NOW, officially, I use Sovtek tubes, as they are the tube purveyor to Marshall, Fender, and everyone else.
I would not use Chinease tubes even if they were free. The bulk of amplifiers I have repaired have been from these cheap tubes going out and taking board parts with them resulting in sometimes over a hundred dollars of repair cost for customers.
The problem is that its not the fact Chino tubes are made as cheap as Bic lighters (use a little bit and pitch them), and they do accross the board sound great (Ruby Tubes like to use them). The problem with them is that Joe tube amp dude will spend 50.00 on power tubes and try to get every bit of life out of them. 30 years ago, tubes had lives of 5,000 to 30,000 hours, but today 2,000 of constant use will spank any modern tube (remember that if you work at a job 8 hours per day, 7 days per week, thats a little over 2000 hours: working musicians).
I would re-tube at around 1,000 of normal use, and half that for max volume users of any modern manufacturer. That way, you are never likely to run into board repairs from tubes Jubilee. :shock: