Sai,

Noticed the GL KT-77 tubes sound like what your describing when breaking them in. Give them a little time. Should be fine after 100 hours.

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Mk 5 will take longer to settle and sound better with time.

Thank you for sharing your experiences. I foresee a few long listening sessions in the near future for sure  :)

I just got my Torii Jr V2  approaching 200 hours.  My process was to use a long play and let it play day and night at very low volume just to get the hours of use.

Initial sound was good but not significantly different from my prior amp. I think this was in part do to my speakers and room being in sync and a well established sound stage.

At around the 100 hour mark things started getting better, ie my sound stage was enhanced, snare drum and cymbal decay was much better than anything I had before.

BTW this is my first tube amp so still sensing the differences

Enjoy the music

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They start off with extended and hanging notes in the mids and highs. Sounds great and wild. Wish they would stay like that. The balance overall levels out nicely. Interesting tube to experience new. I give all new production Russian tubes a little extra time to level out.

Edit: Noticed a rectifier vibration at first. Long story short breaking in GL KT77s were noteworthy. Could just be me. Was interested if anyone else had noticed.

JEC,

Years ago, once I got my Torii 3 system opened and speeded up, GL KT77s became a little too much here... impressive, but a little in the face for my setup and me. But I did love them for the time I had an SE34 and thought their extension, openness, clarity, articulation, and dynamics were quite beautiful with that amp and speakers, etc.

I did take to using 7DJ8/PCC88s for quite a while with my Torii 3 though, giving some similar things but at the inputs... just one of many variables for defining ultimate power tube preferences. I feel sure I could tune and really enjoy a set of GL KT77 now if I had some. But I have stayed with 6L6 types for a long time, and really like those I have for their delicacy and super fine detail/space abilities.

I have noticed heavily made Russian tubes taking their time too, but I do recall the KT77 as comparatively quite good to start off like you and GS. I think this made me less sensitive to noticing as they burn in, their growing more complex with speed, space and finer detail. I do recall this, but not the timing. I can say that here, the GL KT66 was the longest power tube burnin I can remember...well over 200 hours as I recall.

But the GL KT77, pretty open and lively right off... seems it would be a good thing with a new amp, the solid, clean and dynamic presentation overwhelming some of the amp burnin antics enough that they are not as in the way? What JMeader is pointing to seems in the same neighborhood to me... tune the front end to be more solid, complex, spacious and complete, and it can help with system balance while balancing some of the up and downs of burnin. I am always tuning the front end as needed, and have used more open and pretty fast tubes with burnin.

I wonder how much time you have on your MKV JEC. If the KT77 experience was with your new amp, I think the "extended and hanging notes in the mids and highs" could be associated with caps burning in too. Especially with smaller nice film caps as power supply bypasses, and in the signal path, if enough value to act this way (with all the rest), they can lean toward taking a little long to release the clarifying surge they contribute to, and I think burnin can help solve this. How it appears to me anyway.

Sounds really good. Having fun!

You are welcome JEC. I am glad I could be of some help.