Gemini Ampeg amps

[Cljdm@xxxxxxx]

Hi,

    I just Bought a Gemini 1 Ampeg amp, Model G12. Appreciate any information 
from anyone owning one. Harp sounds great through it. It looks to be about 40 
years old. Picked it up for $175 (good buy?).The amp plays well looks decent. 
Has a 12" speaker that seems not to be the original (no identification 
marks). Two channels. One works the bass, treble, vibrato/intensity/speed and 
the echo. Two is just volume,bass, and treble. There are two plugs for each 
channel. One for guitar and one for the accordian on each channel (four 
inputs). I really like the accordian plugs.

     What year is this amp approximately from? And, can I  change the 12ax7 
tubes with au's or ay's? 
    The tubes left to right are:
   7591 7591 7199 12ax7 12ax7 6cg7 12ax7
   Should I go for a whole new set of tubes? Also, the amp has a wax 
tranformer. Should I just leave it alone?

  I am hoping to get this amp singing real nice, since it seems to have the 
capacity to be a great harp amp. Any information or help would be greatly 
appreciated.

                                    Best of everything,
                                                chris