KT-77 vs. KT-66

@jimmy2615 I have a Primaluna Dialogue Premium integrated and have rolled tubes a bit, including KT88’s and 6550’s. I, always, come back to KT77’s. To me, I find KT88’s (Tung Sol & GL) and 6550’s (EH) have more bass, but loose significant detail. KT77’s have it all. I was not impressed with Siemens el34, either. I would like to try some Amperex el34’s double-D getters, but need another matched pair. Also, I would like to hear how vintage 6L6’s sound in a Primaluna. A friend swears by them in his guitar amp.  Though, not the same equipment. 

I've been using my Dennis Had SEP tube amp again lately (I switch between it and a Pass XA-25) which can utilize a really wide variety of "KT" type tubes and I really like KT77s (Gold Lion) in the thing. A fave for sure. I discovered a  forgotten  pair of GL KT66s I bought just before the Russian tube world imploded and recently stuck 'em in the amp...it seems they need a little while to break-in...they're great sounding! Really hard to say if they're better than 77s or to describe the difference, but hey...try 'em! The Gold Lions are great looking tubes by the way.

Concur with wolf_garcia the GL KT77 is a fantastic output tube in a Had Inspire, detail, warmth, linear up and down the frequency range with excellent harmonics (my way of saying sounds great!).  
 

toddnig comments are helpful identifying KT88/6550 differences. More bass, lower mids, loose some sparkle and detail on the top.  Still a great sound depending on the music and mood.  But the GL KT77 is the overall winner, has it all top to bottom good tight  bass, rich warm mids, sparkly highs with detail 20Hz to 20kHz. Like I said earlier, everything the EL34s have but more of it and better.
 

Now I’m curious what a GL KT66 would sound like…oh jeez, here we go again! 

@wolf_garcia Thanks for weighing in. I love the KT77's so much I have two pair. I'm very curious if you hear any real difference with the KT66's because they've gotten kind of expensive and hard to find. The GL's are very very hard to find. JJ is more gettable.

I think the Gold Lion 66s have a little more low end maybe. Although unless I listen to them and quickly take them out and put the 77s in its really hard to tell critical differences, and I generally don’t do that. Suffice to say, after break-in (a day or 2) the 66s really came into their stride and sound great. I can’t say much about the JJs except that a pair of JJ KT77s I bought were just not good at all compared to the Lions. I also have at least 4 or 5 (one died) GL 77s so I’m set with those for years, as well as Tung Sol 7581As, KT120s, etc. I was perusing Viva tubes recently and thought I had to try the GL 66s, and looked in my tube drawer and found a pair I must have bought just before I started using the tubeless Pass XA-25...nice surprise although even at today’s rough pricing for Gold Lions I would have bought ’em. Note my single ended Had amp uses only 2 power tubes (four tubes total including the input 6SN7GTB and a rectifier tube) so tube expense isn’t much of an issue.