Tube rolling is a slippery slope. There is NOT a direct relationship between price and sound quality/results. As a result, it's a good idea to play around at the cheap end of the spectrum first if you are truly experimenting.
OTOH, if you find someone else who has the same unit, and has done some of the "work" for you, you can save a lot of trial and error.
For 6dj8's there are a lot of alternative tube types that might work in your unit, some of which might not be obvious. A good tube seller should be able to suggest some alternatives to match your desired sound profile. For instance, a Siemens 6922 or a Telefunken will be WAAAY different than a Mullard or an Amperex. But you might be perfectly happy with a $15 Reflektor, or a Valvo 7dj8. In other words, LOTS of options.
I'm a big fan of Jim McShane because he doesn't add huge markups and tests/guarantees his tubes. When a pair is "matched" you can be sure that it will be gain-matched correctly, both section to section (these are dual-section tubes) and tube to tube. Unfortunately, Jim doesn't often have many of the more rare and prized vintage tubes. But he would be a good place to start for some inexpensive more recent alternatives that you might be perfectly happy with.
At the other end of the price spectrum is Andy at Vintage Tube Services, or Brent Jessee. These guys sell primo vintage tubes at nose-bleed prices. To some extent, you are paying for knowledge and experience when you buy from them. But if you really want a pinch-waist Amperex 6922, then the one you get from Andy will be exactly that, not a knockoff or rebadged other brand tube. I strongly recommend them if you can pay the freight, but if you have the time/inclination and are somewhat lucky, you may well be able to find the same tubes for pennies on the dollar.
There are some reputable tube-sellers on ePay, but lots of horror stories as well. I've had good experiences with "TubeHunter" who is in the far East and has delivered some pretty rare tubes at nice prices, but they are often untested, or used "pulls" from vintage test equipment. Easy to get burned if you don't know the difference between a D getter or a frame-grid tube. Sometimes its worth paying the premium for experience.
It it were my money, I'd start with someone like Jim McShane first, and start to get a sense of what different tubes sound like in your DAC, before you go spend a lot and are disappointed in the results.
Hope this helps!
Frank
OTOH, if you find someone else who has the same unit, and has done some of the "work" for you, you can save a lot of trial and error.
For 6dj8's there are a lot of alternative tube types that might work in your unit, some of which might not be obvious. A good tube seller should be able to suggest some alternatives to match your desired sound profile. For instance, a Siemens 6922 or a Telefunken will be WAAAY different than a Mullard or an Amperex. But you might be perfectly happy with a $15 Reflektor, or a Valvo 7dj8. In other words, LOTS of options.
I'm a big fan of Jim McShane because he doesn't add huge markups and tests/guarantees his tubes. When a pair is "matched" you can be sure that it will be gain-matched correctly, both section to section (these are dual-section tubes) and tube to tube. Unfortunately, Jim doesn't often have many of the more rare and prized vintage tubes. But he would be a good place to start for some inexpensive more recent alternatives that you might be perfectly happy with.
At the other end of the price spectrum is Andy at Vintage Tube Services, or Brent Jessee. These guys sell primo vintage tubes at nose-bleed prices. To some extent, you are paying for knowledge and experience when you buy from them. But if you really want a pinch-waist Amperex 6922, then the one you get from Andy will be exactly that, not a knockoff or rebadged other brand tube. I strongly recommend them if you can pay the freight, but if you have the time/inclination and are somewhat lucky, you may well be able to find the same tubes for pennies on the dollar.
There are some reputable tube-sellers on ePay, but lots of horror stories as well. I've had good experiences with "TubeHunter" who is in the far East and has delivered some pretty rare tubes at nice prices, but they are often untested, or used "pulls" from vintage test equipment. Easy to get burned if you don't know the difference between a D getter or a frame-grid tube. Sometimes its worth paying the premium for experience.
It it were my money, I'd start with someone like Jim McShane first, and start to get a sense of what different tubes sound like in your DAC, before you go spend a lot and are disappointed in the results.
Hope this helps!
Frank