Looked like it had been a while current to Nov2023 for many postings regarding this topic. Apologies to all concerned if this is not the appropriate way to perhaps raise and discuss this issue again.
WARNING: this is just real world tube rolling in my system using the components listed in my signature. True volume matching was not done, and one tube set’s output is less than the others. This rolling was done in my living room, not a dedicated listening room. No sound treatment for the complicated asymmetric room. I could not cross compare with headphones. I am intimately familiar with the sound of my gear. All tubes were brought up to temperature in the preamp prior to evaluation. I primarily listen to rock, folk, pop, soul, and the jazzier side of rap. Sorry, some though little classical.
Props to my wife for positive opinions in real time during my process.
I use formed plastic automobile detailing tools to gently tease the tubes out of the first part of their travel from their sockets, then gently grasping and rocking by hand their bases, not the glass of the valve.
Tubes I compared: OS matched Raytheon JAN 6V6GTY; NOS matched Soviet PANNO (N’s in cyrillic) 6n6c from the 1970’s; OS matched RCA 6K6GT. My understanding from the vendors were the OS tubes could easily be more than 60 years old. All tubes were tested as new or near new on testers.
I would have liked to find some “bottleheads†to include, but could not.
I began with the Raytheon’s as they have been in the rig for months and their sound is what is most familiar to me. Overall they have a transparent, flat frequency response type character. A clear, pleasant sound that I would characterize as somewhat antique in character. Their output gain seemed in between the Soviet tubes (highest volume gain) and the RCA’s (least volume gain). They remind me of the output of my Crack w Speedball headphone amp with my Sennheisers. Definitely a good thing. Bass was tight, upper bass not in abundance. Easy to listen to at length.
Next up I auditioned the NOS Soviet 6n6c. They sounded more dynamic and not surprisingly also exhibited the most volume gain of the 3 sets of tubes. A slight emphasis in the 4-5 kHz area noticed on voices and piano. Not overly harsh or metallic but there. Their presentation was slightly energetic, yet nicely detailed and refined on snares and cymbals. Nicely defined bass.
Lastly, I auditioned the RCA 6K6GT. My understanding is that the 6K6’s output measures less than the 6V6 equivalents previously mentioned. It took a noticeably larger use of the volume control on the Moreplay to approximate volumes equal with the previous tubes of this review. Certainly in a very usable range without overdriving or distortion. The soundstage felt slightly back in the mix from either of the previous tubes. This was not unpleasant, and sacrificed little if anything in terms of definition. In fact in the end I decided to go forward with this set of tubes for a longer additional auditioning. Initially they seemed to have potential for being the least fatiguing, yet having a nicely smooth detailed balanced tube sound.
I will update this posting as I live with these tubes for awhile.
There you have my initial foray. Not scientific but hopefully somewhat similar to what many of you may do.