Absolutely yes to yout last question, as the three alternatives you named are more linear than a 12AU7.
Best regards!
Best regards!
You should train your mind to avoid generalizations and opinions based suggestions when it comes to tube usage because they each have different specs and benefits. Design for what you need to do and pick the best choice of tubes for it. Forget about good, better, best characterizations. Don't be dumb. Clear your mind. What does the tube need to amplify? What does it have to drive? What PS energy will you give it?
The 7247 is a very good alternative for the reasons you have noted. I've done exactly that for the same reasons. But might be hard to find now. And be rather expensive. For some reason they never caught on in the mainstream.🙂
This is not my thread and it seems you may not have read the original post.
I would refer you to the OP's first sentence which is "Note: This is more of a general question and not specific to a circuit, so there is no schematic."
He seems to want to use a single, dual triode tube, to serve as both input and driver but he's concerned that, as an input tube, the 12AX7 would have too much gain. And he's asking about using feedback to reduce the gain.
Perhaps I'm just ignorant, but my approach would be to try to find a tube that functioned better from the get go without having to resort to a more complicated design using feedback to correct the problem caused by excessive gain.
So, in line with the original question, I'm only offering a general suggestion about some other possible alternatives to using a 12AX7.
Obviously, if one had a particular application in mind, further research would be necessary. But, in general, it would seem to me that using a tube that was better suited to the situation would be preferable.
Thanks for your cautionary advice, though.
New production 7247s (aka 12DW7) are available from both JJ ($17) and E-H ($28). The big dealer near me lists NOS for $19, if they have them in stock.
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I thought pointing out the existance of a dissimilar triode was spot on. But then you went into the other point of comparing the 12AX7 against the 12AU7 based on your impressions.... and then went further in that vain... ?? Take care.
Actually it will stabilize the Plate-Cathode Voltage at something higher than V(led)*Mu. Or >160V for Red and 12AX7. It really wants to sit near 200V. "Stable". But the current will be whatever flows in the resistors due to supply voltage minus tube drop. For 150V supply, hardly any; for 350V supply, a lot. Since most tube gain and drive is related to current more than voltage, this is not stable in its audio properties. (A stable supply would help, but ideally it would reference LED and Mu, not a constant voltage.)
Not ignorant at all. In fact this is so true and important it should be mandatory reading.
The answer to the OP question is: You don't design a stage with too much gain and then band-aid it with FB. You design the stage correctly in the first place. The design should take into consideration all your requirements and may contain whatever amount of feedback appropriate for accomplishing the requirements.
Whether it's too much feedback is a moot point. You will know it's too much when you can't meet the requirements. As said, one lab grade commercial amp with stellar performance has 80dB of gnfb.
Sorry for the late response. This is a hobby for me. You're absolutely right on in regards to my line of thinking. I recently posted another thread with actual design, as crappy as it is. Amp design critique
You'll easily see where my feedback question may have been misguided. I'm trying to learn to model enough before I put another prototype together.