Mixed driver tube for Mcintosh MC275

in my MC275 V with very good results. Musicality and instrument definition greatly improved with the Mullards over the stock 12AX7's. Also found that the amp benefitted from using Audio Research tube dampers on V1, V2 and V5. Tried the dampers on the 12AT7's and really didn't notice much of an improvement, at least not compared to the dampers used on the CV4004's.

I am using Mullard CV4004's in place of the stock 12AX7's in my MC275 V with very good results. Musicality and instrument definition greatly improved with the Mullards over the stock 12AX7's. Also found that the amp benefitted from using Audio Research tube dampers on V1, V2 and V5. Tried the dampers on the 12AT7's and really didn't notice much of an improvement, at least not compared to the dampers used on the CV4004's.

Cheers

I have the MK IV so maybe it is different

The input stage of MC275 re-issue is completely different to old design. In balance input of re-issue, the positive and negative phase is push-pull amplified directly and coupled to output transformer to form a completed output waveform. This new design is to avoid the phase-splitter design in the traditional tube amplifier design. In single-end input of re-issue, the input itself forms +ve phase and use a half of 12AX7 to invert input to form -ve phase. In this case, the signal of +ve and -ve phase is not mirror inverted since -ve phase is suffering distortion produced by an extra 12AX7 amplifier stage. This can explain why the balance input sounds better than the RCA input in the case of MC275 re-issue.

Schematic of MC275 re-issue see http://farm5.static.flickr.com/4037/4204605299_bdfa12827f_b.jpg

I think the RCA sounds better