A/B comparison McIntosh MC275 MK IV vs. MC275 MK VI

Has anyone done an A/B comparison between the MK IV and the MK VI? I had the MK IV with stock preamp tubes and Gold Lions on the output. Sound was awesome with very sweet mids, but lacking a little bass. I just upgraded to the MK VI. I feel that the bass is deeper and tauter and the highs are definitely sharper, but the mids are not as beautiful and fluid as the MK IV. I'd appreciate any thought or comments.
I hope you will try audiograde fuses in your amp. I believei t may be of significant help.
David Pritchard
I have not heard the mk VI, but have the mk IV and I've tried a couple of things.
On my amp/system, fuses had a very marginal impact.
Rolling 12ax and 12at tubes had a significant impact.
Replacing stock kt88 for shuagang treasures had a very significant impact. Maybe even more than with the smaller tubes, but frankly a lot of time went by between one and the other roll.

Including a Bybee on the line-in had a significant impact.

Being a long time owner of a MC275 mk V, I can say that high end fuses do make a difference but one needs to upgrade all 5 and not just the Line fuse although just upgrading this fuse will yield benefits. Inside the chassis on the main PCB are 4 fuses and upgrading these, as well as the line fuse, yields a nice profound upgrade in clarity and musicality.

As far as tubes go, upgrading V1 to an EAT ECC803s had substantial improvements on resolution and upgrading the 12AT7's to Mullard CV4024 was another step up in resolution as well. As for the KT88's, the Gold Lion Genalex are a great upgrade especially over the stock tubes and for the remaining two 12AX7's, season to taste.

A good aftermarket power cord will yield benefits as well as will a good amp stand. I personally use mag levitation interfacing on a sand filled amp stand spiked to the concrete pad underneath the carpet.

If you want more mids, insert the Jensen copper foil coupling caps in place of the stock caps. no comparison.

I have the mark IV and after many different tubes in this amp I have found that it sounds the best in this configuration.  V1 Mullard long plate Square Getter or Telefunken smooth plate in V1, Telefunken smooth plate V2 and V5, RCA triple MICA 12at7WA V3, V4, V6, and V7.  Vintage Tung Sol 6550.  Tried the Treasure tubes and found them a bit on the soft side for me.  YMMV.
I've owned both the IV and the LE (50th anniversary Mc275, virtually identical to the VI except for cosmetics).  The LE and IV have the same basic character, but the LE has deeper and tighter bass as well as more extended, cleaner high frequencies.  I ran both amps with the same tube set and got the results described above.  Hope this helps.
Sheesh guys, I retubed my MC275 Mk IV because of bad Chinese stock tubes as soon as I got it due to a problem.  I’m using Genelex KT88s from the 60s NIB matched quad and rca 12at/ax7s they appear to be black plates. I’ve got 180 hours on all tubes now.

My MkIV has incredibly hard hitting tight bass, outstanding mids and the highs are amazing.  I’m running the Mac new reissue C22 and driving University Sound 315C series 200s!  With this tube compliment and the rest, I’d say there are few amps that could touch this one, whatever mark number they are!!