Electro-Harmonix 12AX7 Review.

These are not relabelled Sovtek 12AX7-LPS tubes. There is a marked difference in construction and performance. The 12AX7 EH has a nice balanced sound, fairly low noise floor and excellent performance in terms of microphonics. The lack of microphonics may be in part from the return of the shorter plate structure or materials. I've had some samples that were tried in various amp stages. Pre-amps, tone stacks and phase inverters, a winner in every location, although I like to use a 12AT7 for reverb circuit drivers due to their lower gain rating (just a personal preference of mine). I have used the EH to successfully tame amps that defied all other attempts to kill microphonics and unwanted feedback. This tube is a winner, buy 'em and try 'em, they may be just the piece you've been looking for.

Information from thestoretube.com