Why 6dj8 tubes in the phono stage?
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BAT makes a fine phono stage. I think you'd want to stay with the vkP5 or vkP10 models without the super paks if you want to tube roll. Also, they only have balanced outputs.
Aesthetix uses them for output drivers, 1 in each channel. I don't remember how much the Rhea responded to changes in the 6922/6dj8 tube.
Manley Steel head uses a few 6922's. You'd have to check with them to see if the 6dj8 is a direct replacement in their circuit. Most times it is, but it's always better to ask.
OK. 0.35mV then- you are going to have difficulty with a 6DJ8-based phono section. The problem that you run into is that 6DJ8s, 6922s and the like aren't designed for audio so you run into noise and microphonic issues which at the very least color the sound of the preamp.
The 6DJ8 is difficult also from a design perspective as it has a mu (gain) of about 33, which makes it a medium-mu triode. High-mu triodes, like 12AT7s and 12AX7s, allow for high gain with low noise and low microphonics; IOW low coloration.
If I were you I would not worry about the tube type so much and concentrate more on who has a tube phono section that can handle a moderate to low output cartridge like you have. If it doesn't use 6DJ8s you can always put them up on eBay...