I do not own either amp but I do own an Octave V70SE integrated. Mine came with SED KT88's and I also ordered a quad of SED winged C 6550. The SED 6550 is a very linear sounding tube where the KT88 is a little warmer. Next I got a quad of the GL KT88 re-issues. The GL's fall somewhere between the SED 6550 and KT88's. Later I scored a quad of Tung Sol 6550 solid black plates. Wow what a difference. More like the SED EL34 - magical mid range ever so slightly rolled off highs and not much in the bass dept or power when compared to the SED or GL. The TS 6550 solid black and grey plate have the bass and the power the EL34's lack. Later I picked up a quad of Gec KT88's. Very linear but with a tighter low end and more 'sparkly' for the highs.
That being said I do not own or have even heard the GE 6550. So to summarize I have to say the SED 6550 - Gec KT88 and GL KT88 are all more 'solid state' sounding where the SED KT88 and Tung Sol solid black and grey plates are more 'tubey' sounding. Now if you like the Gec KT88 sound and want even more of the same try the EAT KT88's. Another KT88 that I have is a KR Audio branded Tesla. A hair more of the Gec KT88 but not quite an EAT. So if you prefer the SED 6550's the Gec KT88 is a big step up. Sorry I can't comment on the GE's but I'm trying to give you an idea of the differences between the SED 6550 - GL KT88 and Gec KT88's.
Last to me all tubes sound good but there are sonic differences between types and manufacturers. So types like 6550 or KT88 can not be lumped into a particular sound category. Another Great tube I have is the Ei KT90 type 2.
That being said I do not own or have even heard the GE 6550. So to summarize I have to say the SED 6550 - Gec KT88 and GL KT88 are all more 'solid state' sounding where the SED KT88 and Tung Sol solid black and grey plates are more 'tubey' sounding. Now if you like the Gec KT88 sound and want even more of the same try the EAT KT88's. Another KT88 that I have is a KR Audio branded Tesla. A hair more of the Gec KT88 but not quite an EAT. So if you prefer the SED 6550's the Gec KT88 is a big step up. Sorry I can't comment on the GE's but I'm trying to give you an idea of the differences between the SED 6550 - GL KT88 and Gec KT88's.
Last to me all tubes sound good but there are sonic differences between types and manufacturers. So types like 6550 or KT88 can not be lumped into a particular sound category. Another Great tube I have is the Ei KT90 type 2.