I owned the Octave V70se and later the V110 along with the black box. The black box lowers the noise floor while adding a hair of headroom. As far as sound quality it depends which tubes are used. When I got the V70se the stock tubes were all SED. I had the EL34 6550 and KT88's. SED is no longer in production. Of course the V110 came with TS KT120's. The KT120's were my least favorite tube. There is a switch on the back that kicks down the plate/grid voltage so lower power tubes can be used like the EL34-6550-KT88.
That said the EL34 has a to die for midrange but really lacks lows punch and the highs are slightly rolled off. 6550's very linear from top to bottom with good punch. KT88's is warmer with good punchy lows. Mind you those were the stock tubes. GL reissue KT88's sound like a cross between the 6550 and KT88 (very good for the money). EAT KT88 Diamonds are the most linear with a tremendous amount of detail but super expensive. Ei KT90 has a huge soundstage and a midrange that is close to the EL34 while having great lows and highs. The Ei KT90's had no problem running in high power and sounded better with the V110.
That said a lot will have to do with what speakers you're driving. When I had the Dyn C1 and later the Signatures I preferred the original TS 6550 solid grey and black plates. Very warm sound with a killer midrange. The EAT did not sound very good. Ei KT90's were very good and I swapped them with the original TS 6550's a lot. The KT120's were very shouty and sounded too much like SS. Original KT88's are very linear and detailed like the EAT's. Not a good match IMO with the C1's. Later I got Raidho D1's and now the D2.1's. Well those TS 6550's sounded very mushy. The Ei KT90's and original KT88's were my favorite hands down. As far as EAT I lost too many (5 out of 8) in less than 2 months while I had the Dyns so I didn't have a full quad when I got the Raidho's.
That said I don't have Octave anymore. With the Dyn's I had no problem even when pushing the C1's very hard. The Raidho's on the other hand did start to peter out when pushing the volume to the max. Now IMO tubes should not be used if you want to try to get to concert levels. But if you mostly listen to levels 85db or less tubes are heavenly.
That said the EL34 has a to die for midrange but really lacks lows punch and the highs are slightly rolled off. 6550's very linear from top to bottom with good punch. KT88's is warmer with good punchy lows. Mind you those were the stock tubes. GL reissue KT88's sound like a cross between the 6550 and KT88 (very good for the money). EAT KT88 Diamonds are the most linear with a tremendous amount of detail but super expensive. Ei KT90 has a huge soundstage and a midrange that is close to the EL34 while having great lows and highs. The Ei KT90's had no problem running in high power and sounded better with the V110.
That said a lot will have to do with what speakers you're driving. When I had the Dyn C1 and later the Signatures I preferred the original TS 6550 solid grey and black plates. Very warm sound with a killer midrange. The EAT did not sound very good. Ei KT90's were very good and I swapped them with the original TS 6550's a lot. The KT120's were very shouty and sounded too much like SS. Original KT88's are very linear and detailed like the EAT's. Not a good match IMO with the C1's. Later I got Raidho D1's and now the D2.1's. Well those TS 6550's sounded very mushy. The Ei KT90's and original KT88's were my favorite hands down. As far as EAT I lost too many (5 out of 8) in less than 2 months while I had the Dyns so I didn't have a full quad when I got the Raidho's.
That said I don't have Octave anymore. With the Dyn's I had no problem even when pushing the C1's very hard. The Raidho's on the other hand did start to peter out when pushing the volume to the max. Now IMO tubes should not be used if you want to try to get to concert levels. But if you mostly listen to levels 85db or less tubes are heavenly.