KT88 recom. for quicksilver mini mono's

I only rolled KT88's in the Mini-Monos. I was quite happy with the performance of them so did not try the warmer, more tubey 6550 approach (at least that's how I'd guess they'd sound). Perhaps I was missing out, but I really liked those amps with the KT88's in them. As I said, I ended up with JJ's. Clean and punchy and versatile, those amps mated well with many speakers. What did you end up preferring, Elsneb?

Jax2, Got to wonder what you mean by "tubey 6550 approach"? In compared to KT90's yes, but in comparison to KT88's? I would think the KT88's, at least the ones I have heard, have all sounded warmer, more sparkly, and less linear than 6550's. Did you have something specific in mind?

I once tried some GE 6550 in my VAC amp. Compared the the KT88, the 6550 were rolled off and had looser bass. I would characterize the VAC stock KT88 tubes as sounding more linear in that particular application.

Tvad, FWIW, in three different amps, each of the 6550's and KT88's (both SED's) had the same sonic signature, albeit the overall sonic preference was different because of the design of the amps (Cary, Sonic Frontiers, & Primaluna). The KT88's had a warm(er)upper bass, and bright(er) in the upper mids. The KT88's seemed a bit more extended and had an overall tone much more (to me) reminescent of 'tubey sound'. The 6550 has a slightly rolled top end, neutral mids, and deep powerful bass without upper bass emphasis. The sonic's of the 6550 reminds me of the KT90 except for the roll off, and maybe a bit more power from the KT90 in the bass.

My observations about the overall nature of tube types seem consistent (to me anyway) with comments I have heard from others. Obviously different brands of each type will sound different and the application (to amp) is critical. FWIW I bought the Cary mono's with KT88's - the bass was big dense thumps, I replaced these with 6550's and the bass became clean, impactful, and linear. To compensate for the soft uppers, I put some compensating tubes in the driver position in the amp as well as in the source(s) used with the 2 amps in which I use the 6550's. Now, with one amp (SF) the KT88's provide a perfect couple with a Wadia CDP driven direct. I've never liked 6550's in that amp - just too cool for me.

JMHO, I'm sure everyone has their own valid opinion.

Your observations and mine illustrate that there is no universally applicable observation, which brings me back to my original point that tube amps are generally voiced with a particular type and brand of tube, and it's likely that any other tube used in that amp will not sound as well as the tube that was used to voice the amp.