2. amps-preamps
  3. 1175279050

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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128x128nsgarch

Showing 6 responses by mrtennis

mrtennis
3,295 posts
 
gentlemen:

i have had repeated discussions with chuck hinton about the design of the circuits in the 275 amp and c 200 preamps.

his comment is that the design of the tube circuit makes both amp and pre amp tube insensitive. i have had the c 200 preamp for several weeks and tried 4 pairs of 12ax7, namely, rca 12ax7 grey plate, rca 575a black plate, mullard 12ax7, tungsol 12ax7 and sylvania 12ax7. differences were very slight.

i have not yet experimented with my 275 mark v.

there are 2 types of errors in listening. one may hear something which is not there or fail to hear something that is there. i am very puzzled, as i am very sensitive to the upper mid and lower treble frequencies.
mrtennis
3,295 posts
 
my mistake. i am referring to the c220.

regarding the 275. chuck hinton told me a funny story. he said a customer placed 12at7 tubes in the sockets marked "12ax7" and placed 12ax7 in the sockets marked "12at7".
the result ? no damage to the amp or tubes.

i have several sets of 12at7 and several sets of 12ax7. i will keep an open mind and see if i hear any meaningful differences.

my experiences so far with current production tubes components is that replacing stock tubes does not significantly alter the sound. that is, what differences do occur don't matter.

my experience includes cd players and preamps.

i would love to be present at some of the sessions cited by audiogon members where several sets of nos tubes replaced stock tubes. it is possible that my threshold for experiencing meaningful differences is greater than that of other audiophiles.

i will report back after i have investigated the effect of replacing the stock 12at7 and 12ax7 following the break-in of the mc 275.
mrtennis
3,295 posts
 
gentlemen:

there is a question regarding the compatibility of other 12 volt tubes with the 275 circuit. i believe that a 12ay7 could substitute for a 12ax7. what about a 12au7, might that work in lieu of a 12at7 ?

is anyone willing to try a 12ay7 and/or 12au7 ??
mrtennis
3,295 posts
 
i realize this is partially off topic, but i substituted a pair of 12ay7 for the 12ax7 in the c220 preamp. i also substituted a pair of 12au7 for the 12ax7 in the same preaamp. the preamp did not blow up and the tubes were not damaged. in fact i preferred the 12ay7 to the 12ax7.
mrtennis
3,295 posts
 
the gain differences i noticed in the preamp, were of minor consequence. what happens in the amp if i substitute 12ay7 anf/or 12at7 for the 12ax7, will the changes in gain be of more concern than those accruing from the same substitution in the preamp ?

thanks
mrtennis
3,295 posts
 
changes in gain structure can sometimes affect the performance of a stereo system. i have been told that 12at7 and 12ax7 tubes were interchanged, by "accident" with no harm to the tubes or amplifier. it is possible that using 12ay7 might provide a preferred presentation than a 12ax7.

our hobby is based upon personal preference. "playing around" with 12 volt tubes may be a way of attaining a "sound" that is desired.
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