KT-77 vs. KT-66

Thanks.  I thought I’d also add, after noting some of the comments about 6L6s, I have some NOS RCA blackplate 6L6GCs.  These sound like JJSS was describing above.  The KT66s are a lot more dynamic and not as warm in my system.

@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.