The two tubes have the same pinout and can be freely swapped in that sense.
However the gain of a 12ax7 is 100 whereas a 12at is spec'd as 60.
Also a 12ax drives about 1 ma whereas a 12at drives 10mA.
So put in an ax if you need more gain, an at if you need more current drive capability.
However the gain of a 12ax7 is 100 whereas a 12at is spec'd as 60.
Also a 12ax drives about 1 ma whereas a 12at drives 10mA.
So put in an ax if you need more gain, an at if you need more current drive capability.
Here's a crazy idea: if the circuit calls for a 12AX7, use a 12AX7. They aren't exactly hard to find, and excellent versions are relatively inexpensive.
OK if you want an FX box, or the original design was wrong and just happens to better suit the 'wrong' triode. If the original design was correctly optimised for one triode, then putting another one in with completely different characteristics will give poorer performance.
Alternatively, just add a pot to fiddle with the bias and dial in whatever amount of distortion you prefer.
Alternatively, just add a pot to fiddle with the bias and dial in whatever amount of distortion you prefer.
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