Pablo, there were a couple of older threads discussing the GT preamp, did you see those?
I, too, had a GT back in the day when they were still in production. I coupled it with a QSC 1400 power amp.
I bought mine because of an interview with Stu Cook of Creedence Clearwater Revival that appeared in Guitar Player back in the late 80's. Stu was really into the sound he got with the GT.
I would agree that the preamp was very clean and tight sounding, with a bit of tube warmth. It's not SVTish at all. It was pretty much the forerunner of the later SWR heads with the same panel and control layout, and to me, the sound was almost identical to the SWR SM-220, SM-400 and SM-500 heads, if that helps.
I would love to have another one. I don't need one, but I do miss the one I sold. I sold mine to get an F-1X, with one rack space size and a better tube tone, not to mention simpler controls. But I'd still love to have another GT.
Hey, if you are getting back into rack setups, Pablo, this is a really nice preamp. You will dig it. If you don't, you will be able to sell it here on Talkbass. In fact, keep me in mind for the #1 slot.