I agree with Nate that mu on this tube is way to high for this to be a reasonable preamp. This is best used with high Z phones. Quote: Originally Posted by -=Germania=- /img/forum/go_quote.gif Also, anyone know any other compatible dual triode tubes?. Unlikely. There are a 5V (5J6) and 6V (6J6) version, and lots of variations on the 6V version, but none of these can be used here without circuit modification which will destroy the elegance of the heater supply/biasing mechanism. You could use the triode section of a 19CL8 here (other section is a tetrode). It will still make a lousy preamp (mu=40), and it might make a lousy headphone amp too, but the heater will work the same, and the triode section might work. Same for the 19EA8 (same triode as the 19CL8, but has a pentode instead of a tetrode for the other half.) Neither will like the low voltage. I'd get the thing built before you start thinking about swapping tubes in and out.