Originally Posted by sturob
I've got a single pair of these tubes which actually seem like a very nice 6SN7 variant. They have two side getters, directly opposite each other and at right angles to the plates (meaning, you can look at the flat side of the plates, but the gap between the plates if you're looking at the edge is obscured by the getters). Why two getters?
the question should be - why not?
Actually, no one outside of the engineers/designers behind that tube will likely know the answer to that question. I suppose the best answer for now would be:
because they can.
Originally Posted by sturob
Ilso, what's up with this tube? Seems like RCA made 6SN7GTs for quite a while, made the GTAs for a very short time, and then moved right into GTBs. Is my perception correct?
Yep - 100% correct. GTAs were never very popular and were quickly superceded by the better-rated GTB. My understanding is that GTAs took time to succeed the GT type (much like how leaded petrol was phased out in favour of unleaded), and by the time the phaseout of GT was complete, GTBs were already on the market. Kinda like how we all jumped from CD to VCD while leaving LD on the wayside.