Tube rolling, Macintosh MC275 Mk IV

I know this is a '275 thread but I wanted to share some of my anecdotal experience regarding tube rolling in Mac gear.

But first...
I was at the dealer and we unpacked the large MA2275 first to make sure everything worked. Then the dealer and I started inserting the 12ax7/t7 tubes into the sockets. We didn't know at the time that we placed the 12aT7 into the 12aX7 sockets and vice-versa for the other 12aT7 sockets... we didn't know at first and we listened for a few hours... we (including the other salespersons) were marveling at the sound and then a customer came in, looked at the amp and said, "hey you got the toobs wrong!" D'oh! After all that, there was no apparent damage to the circuit or the tubes as far as we could tell.. the resident technician yelled at us and then also marvelled at the lack of damage (and the good sound).
So we re-read the labels this time ;-) and re-inserted the tubes the correct way. More listening ensued and lots of customers drooled over the sound of this integrated amp. This was the first 2275 the dealer had ever ordered so it was a special treat for us to actually unpack and audition it at the store ;-)

... So the folks at Mac gave me the same story: "Tube rolling is futile..." Of course I was more tempted then ever to try rolling some KT88s. So out came the Mac toobs and in went some beautiful JJ KT88s kidnapped from my Cary Rocket 88.

Normally I'm open minded when it comes to these matters, and I was prepared to believe either side. Would Mac be right or would audiophiles save the day? To be honest I didn't really want to hear ANY differences because (selfishly) I didn't want to take my Rocket 88's tubes out of service in my other system. Also, I was very satisfied with the sound from the 2275 so why bother...

Well! I'd be darned if I didn't hear a significant difference from the JJ tubes. The most significant difference was a more extended, impactful bass. The soundstaging was a bit deeper and the highs slightly more extended. Wow! I was expecting at the most some small differences in tonality, but not of this magnitude.

I haven't even begun to roll some 12axxx tubes yet, and I'm sure there will be some sonic differences as well. The bottom line is that there ARE discernible sonic differences between tubes when rolled in Mac gear, just like any other piece of gear.

best,
-Greg

mullard cv4004's and cv4024's go very well with my Mac2102's. Takes away a little of the sizzle from the stk Chinese tubes and maintains great transparency

Downunder, I'm currently A-B'ing some Mullards and Telefunkens in the 12AT7 positions (see original post) and I'll report back. They seem very nice and open -- it might be a toss-up. We'll see (I mean, hear!)

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 ??

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.