Audio Research VT100 MK1 and LS15 HELP!!!

FWIW, Some European sourced small tubes do flash on turn-on. Not at all unusual and it is not significant. I suspect, as others, that your problem may be speaker location (set up in your room) combined with the basic difference in the sound of your new electronic’s. Audio Research components are not known for warmth and unless your system and speakers set up are synergistic and properly set up they can sound cold and clinical, much as you describe, especially compared to your old Mac. I’m an old ARC advocate but I dropped out of that line some years ago for just that reason. It is also possible that your ARC amp is just not one that works well with your KEF’s.

Take a break from your assumption that your components are faulty and that someone has lied to you. Think more about speaker set up and trying to get them (and your listening position) to sound better by properly locating them in your room, Do some research on set up. If you think you need help with that issue, just ask. Many folks here would be happy to help.

Good luck.

Firstly, I overlooked your comments about the LS15 going into protection frequently. This could well be the result of the V3 6922 flashing/sparking. If the LS 15 doesn't require re-biasing you can easily change this tube yourself with like kind and quality. ARC is correct, this Sovtek 6922 doesn't flash on turn on. FWIW I don't think this tube needs to be re-biased. Ask ARC.

Re the loss of bass response, as stated earlier, I think it is a fundamental difference between your Mac, an old vintage tubed receiver known for overblown low frequency response, and a modern amp/preamp known for its more linear, cool, and for many, clinical response. The basic difference between the two is huge! I suspect that you have just made a fundamental beginner mistake, and we all make them, of assuming that what we hear elsewhere will be what we hear in our own homes, but to our disappointment it does not. Been there, done that!

 This is especially so when the seller has taken great care to match and set up his audio system. A good audiophile can obtain excellent results from fairly ordinary stuff because of his basic understanding of his stuff,  how it all synergizes, and the requirements of his room for proper set up.

That said, in order to optimize the bass response of your current stuff, I would run your speakers off the 4ohm taps. I would buy a SPL meter and a test disc  and insure that you speakers are not located in a bass null (and at the same time help pin down getting the best overall frequency response). I would also buy Robert Harley's book on audio for a good primer about audio. 

Well I did a little on line reading regarding your speakers which causes me to suspect the combination of your ARC stuff and the KEF may be your problem. Your speakers seem to be considered ’neutral speakers’ (at best). You seemed to like them when driven by a (very) warm vintage receiver). You are hearing the results of you amplification choices quite clearly. You seem to like a warmer toned system’s sound but with better resolution than you get with the old Mac.. Very common in audio.

Now you change to electronic’s which, tonally speaking, might be voiced to be neutral (at best, IMHO, very cool). So you are doubling down, so to speak, and get the sound inherent in both. For you this sound is not synergistic in that it doesn’t produce the tone you want, not that either the electronics or the speakers are wrong, they just don’t sound as you would like when combined. I would suggest that most of us have been there and done that. I certainly have. That is why most folks will recommend ’matching’ your speaker and electronics. Arbitrary buying will not get you there.

BTW, regarding 4 ohm taps. I’m a bit put off by KEF’s ’recommendations re using only the 8 ohm taps. I could understand why they think your speakers might sound best a 8 ohms (perhaps they think the 4 ohm tap might unbalance their preferred sound) but I know of no reason you should not try them. Your speakers may have have a nominal 8ohm rating but this is far from indicating that they have a minimal 8ohm ’curve. Reviews point out that they have a minimal ohm droop to 3.8 ohms. Were I you, I would research this issue before I just walked away from it based on someone from KEF’s opinion. I like warm toned systems and have most always operated off 4ohm taps.