does groove tubes make a different version of the 12ax7R? called the 12ax7R2? if so, what are the differences?
Groove Tubes does not make there tubes. They are bought from different companys and Groove Tubes slap there name on the tubes. Check out www.thetubestore.com for more info and you will see for yourself. They should have all the info you are looking for.
If you plan to use a Groove Tube in your bass amp, by all means go for the GT-ECC83, it's the best sounding GT IMO, do a side-by-side comparison and see for yourself. Whatever you do, don't get the GT-7025, it's awful IMO.