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RE: Are There Any Issues Using 12au7 in Place of 12ax7s?

Posted by JimL (A) on April 2, 2016 at 22:34:02

In Reply to: Are There Any Issues Using 12au7 in Place of 12ax7s? posted by jaydacus on April 1, 2016 at 16:34:08:

As the others have pointed out, the 12AU7 is a much different tube. It is designed to be relatively linear at a much higher current than a 12AX7 uses. If you plug it into a 12AX7 circuit it will likely be running at a much lower current than is optimal and hence will be distorted.

As a general rule, circuits are designed to work best using the tube that is specified in the design. Plugging in a tube of the same type but a different brand is perfectly OK. Plugging in a different tube type usually results in sub-optiumum performance, e.g. less gain, more distortion, etc.

The tube designers who I have read commenting on substituting one tube type for another generally have a low opinion of the whole idea. It's like assuming that a major league pitcher can replace an NFL quarterback because they both throw a ball.

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