Purchased 3 of these tubes for my Aguilar DB751 bass amp. Compared to the Electro-harmonix 12AX7EH tubes that came in the head from the factory, the Mesa tubes give you better mid's and high's. Low end is very solid, and I could not detect any change in tone. The Mesa tubes are high gain, even more than the stock tubes. Overall, I feel the Mesa tubes are an upgrade, and I would not hesitate to buy them again.