I bought two of these tubes for my Engl Savage 120 to solve two different issues.
The Engl Savage 120 has a passive parallel effect loop, which means that using it can affect the core sound of the amp greatly. Even if the effect loop is configured to run 100%wet.
Using a 12AT7 tube in the effect loop instead of a normal 12AX7 tube, will provide more current flow which helps drive pedals and rack units. Using the effect loop sounds much better now, and if i am careful with finding pedals which match the impedance of the loop, then i cant even tell that i am using the loop anymore (apart from the effect of course ;) )
The second issue i wanted to solve, was to tighten up the power amp section. I have the an old 2009 model, which comes with the "small" output transformer. The newer versions come with the same output transformer as the Invader, which is oversized for this amp, and therefor super tight even with lots of low-end and gain.
But upgrading the output transformer of an amp is super expensive and somewhere along the way i picked up the tip that a 12AT7, used as a Phase Inverter, could help tighten up the power amp section of an amp. Both because it's lower gain than a 12AX7 but also because of it's increased current output.
Installing it actually made such a huge difference that i started having trouble controlling the amount of low-end available when using the Depth Boost. But with a bit of tweaking i found the sweet spot, and the amp is now super tight, while still having a lot of body.
