Tube rolling, Macintosh MC275 Mk IV

But first, I just got the following email from a friend with a new Mk IV (driving Vantages) who had just tried a few NOS 12AX and 12AT tubes I mailed him (he knows who he is ;--)

WOW, I was not prepared for what I was hearing, the first thing that came to my mind was"snap" the music came at me with an energy that was not there before. I soon realize that the music was a lot more dynamic. Meaning there was more treble energy yet still maintain a quality that was silky smooth. Yes there was more detail and nuances that was not previous heard. I wanted to go through my favorite recordings to hear what I have been missing. There is further separation between instruments with ample amounts of air that only enhances the listening experience. In other words I like it, I will listen more tonight and tell you about the improvements. I can see why tube rolling can be fun

I've done some extensive listening/rolling, and have included friends and neighbors in the project -- some with even better hearing than I. Here are my/our conclusions from tubes (including the stock tubes) actually auditioned so far. All twin triode tubes (AX's and AT's) had matched triodes. All pairs of tubes (AT's and KT88's) were matched as well:

12AX7
RCA -- 1957 smoothplate, blackplate, longplate (new, tested over 100%)
Amperex -- Orange Globe, made in Harleen Holland (tested 95%)
Telefunken -- Smoothplate, greyplate (tested 90%)
Mullard -- not included (yet)
12AT7
RCA -- 1957 ribbed, greyplate (new, tested over 100%)
Amperex -- not included (yet)
Telefunken -- ribbed, greyplate (new, tested over 100%)
Mullard -- tried, but not fully A-B'd
KT88
Penta Labs -- KT88SC, new matched quad, (tested over 100%)
GE UK -- NOS: GEC, Genalex, Gold Lion/Monarch (not yet, maybe one day soon if I'm lucky)

Tube groups were rotated in all possible (at this time) combinations, using the Diane Schure/Count Basie Orch. GRP-LP, Track: "Travelin' Light". (system link below.) It was fun. Tedious, but fun! There were some combos that were very close sonically, but the unanimous, winning configuration (after many, many "let me hear that agains") was:

12AX7: RCA -- 1957 smoothplate, blackplate, longplate
12AT7: Telefunken -- ribbed, greyplate
KT-88: Penta Labs -- KT88SC, solid plate, 3-getter

Better than a MC275 MKIV, with stock tubes, out of the box? You have absolutely NO IDEA !! If you want to give it a try, this will save you some time and money; at the very least, give you an excellent place to start ;--)
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