Difference in sound between Siemens e88cc and e188cc?

HI,
E188CC round getter sounds more like Amperex (USA).
A Frames sound more like Cca with more speed and closer to Voskhod 6323P mid 70's.

E188CC is a better tube overall more dynamic better bass with a more vivid presentation. All the positive traits of e88cc with more effortless sound and quiter. Soundstage is wider.
I dont find e88cc astringent or sterile if that is what you mean but E188CC has a fuller character.

HI,
OK this difficult as there are many variants. 
In this family the E88cc is the more vivid one with a big soundstage and open transparent feeling sound. E188CC is more relaxed and easy going with better bass (exception Amperex Holland PQ 2 STAR 7308/E188CC). They sound more esoteric than Siemens and present information a bit upfront. Quiet tubes.
Though Siemens are more consistent in sonic signature over a wider period I cannot say the same of Holland and USA ones.
All sound amazing up to 1963-1964  after that they loose some magic, not much.
Propably metals were different though tooling the same.
I believe that same tooling created Dutch tubes, French tubes, British tubes, USA tubes, Indian tubes, Yugoslavian tubes, all different and of course with different coding.
Check the coding to see what is the actual tube.
French ones are very energetic even the E188CC, a nice alternative if you want that.
What to choose, I cannot say, depends on system, and how far you want to go with tube rolling ( and pocket) but a hard pressed answer:
Holland E188CC VR5 VR6 code
S&H E188CC G1 G2 G3 code
Amperex USA 7308 VR1 -VR5 code
Holland E88CC 7L6 -7L9 code
Amperex USA 7L6 -7L8 code
S&H E88CC A1 A2 code
Mullard E88CC 7L1 code
Dario E188CC VR7 code
I am not listing here the D getter ones for astronomic pricing they seek, but the best were the Holland ones from 1958.
From what I have learned Nos tubes are hard to find in excellent condition and noise free.
E188CC is more rugged in construction and is more balanced between the sections.
Generally a more linear sound comes from S&H, Mullard E88CC/01, Russian tubes and the more colourful from the rest. Every system is different and matching a good task. 

HI,
Mainly more energy in upper regions.
Something else is the ECC88 having more energy on top, lighter bass, even some have better mids compared to their bigger cousins, but are more prone to noise have more hiss and you have to check they can withstand the supplied voltage in circuit otherwise they will fail quickly. 

HI, 
Solid Disc getter had Siemens e88cc, E188CC after 1970 and valvo Hamburg e88cc and 6201 before.
Prior 1960 Philips variants and Siemens had d getter ( or square getter).
Dimple disc getter appeared end of 60's amperex ECC88, dario miniwatt e88cc, rtc e88cc, Mullard E88CC, E188CC, cv2493, cv2492 from 1969.

Hi,
I searched for info and nothing comes up that's even more strange,
most propably 1 variant for a true very limited production as before 60's (58-59) Siemens had only d getter on 45 inclined and then straight post.
Nobody has seen it. Rarity though does not mean better sound.

HI,
Never tried a d getter Siemens E88cc so don't know their signature. I haven't seen same brand E188CC and believe never existed as E188CC came later. 
Dimple disc has a softer sound on top except the Mullards and is common in Philips family tubes.
Generally Halo getter or round getter has more pronounced mids and d getters are sounding more extended on top.
Please follow my other posts and you have the complete picture.