Differences between 12ax7 vs 12au7 – other than gain?

1/28/2000 4:16 PM

lion

Differences between 12ax7 vs 12au7 – other than gain? In an attempt to lower the gain in a Vox-style preamp I’ve found that I really like a 12au7 in the second position instead of a 12ax7.   (V2a = second preamp stage. V2b = cathode follower driving the tone stack)     I know that 12au7/12ay7’s are more commonly used in the first position and I have tried that too - but I like it better in the second position in this amp.     But now I’m wondering about the use of a 12au7 as a cathode follower and a few other things:     1) I can’t recall I’ve ever seen a 12au7 used as a CF - is this a coincidence, or is it just not suitable - or am I missing something here?     2) What are the differences between the two – other than the gain (19.5/100)?     3) I seem to remember something about added stress on the power supply with 12au7’s – is this correct?     4) Of course I could put the 12ax7 back in and drop the gain (say with a split load plate resistor) into the cathode follower - to simulate the lower gain of a 12au7. Would this be a better solution from a tech point of view?     There seems to be a limited selection of 12au7 tubes which certainly speaks in favor of the 12ax7 solution.   Anything else to consider?     Any advise or comments will be appreciated?   Lion