McIntosh MC225 questions


These amps are my favorite. I have two in monobloc mode. A C-41 is the pre, Tannoy DC3 speakers, and Ridge Street audio cabling. Sources: a VPI TT, & a MacMini to Ultra Fi USB DAC (a very satisfying combination especially with ripped CDs into AIFF).

I have some questions for experienced users:


Other than the 7591 power tubes (I'm using matched EHs right now), from your audio point of view which/what other of the amplifier tubes reveal a significant difference when tube-rolled: the two phase inverter tubes: the 12au7's?; the one voltage amplifer tube: the 12AX7?; the two drive amplifer tubes: the 12BH7s? I have NOS RCA blackplates in there mostly (as I recall).

If in your experience some or all made a difference, what in your experience in your system was that difference and what tubes did you settle on?

I've changed the fuses (HiFi Tuning), ok but nothing to get excited about; changed the power cables (cryoparts IEC adapters) to IEC Kubala-Sosna Fasicinations (significant difference in clarity and dynamics over-all); and updated (Terry DeWick) the caps, etc. as per his recommendations.

Generally, this system is the soul-satisfying system!

Thanks for your points of view,

:) listening,


I also have two Mc225's in mono mode. For tube rolling the 12ax7 is the most noticeable change from tube to tube. The 12au7 less significant but you will notice. I did not notice a change with the 12bh7's but I did not try to roll from grey plate to black plate. I think you would hear differences between the two.

I've rolled 1950's long plate mullard 12ax7 with 1960's bugle boys and smooth plate tele's and I seem to like the teles. But they all have their strong points and make for some interesting listening experiences. You really get to know you equipment

Hi Apachef1... what was it you noticed or preferred about the smooth plate tele 12ax7?

:) listening,

More life like vocals and 3d sound staging. The amperex and mullard were stronger in the bass and more of a forward midrange presentation. Tele's has much smoother highs. These are very small differences and will only be noticed if you have very revealing speakers.
I put tele's 12au7 and 12ax7 in for my tube rolling. i think once you are happy with a certain 12ax7 replace the 12au7 tubes with that same brand and plate constuction. it will enhance the sound a little more.
Mixing the brands gets interesting and it all becomes a matter of what you like. I do find myself changing it up every six months or so but always seem to go back to the tele smooth plates

thanks Apachef1... I nabbed a couple of 12ax7 Mullard 4004s out of another preamp (has two sets, one for high gain, the other for phono... took the phono set out) and put them in the two MC225s... what a surprise... I'd say the result was exactly as you described in your post above... stronger bass and more forward midrange (including more air and pointpoint imaging in the highs).

thanks... have a great Thanksgiving...

:) listening,


Use a Ram Lab matched set of Tungsrams. Also like the Teles but they tend to be a little darker. Use Amperex 12ax7s in my other amps but have yet to try them in this circuit.
Using a nice quad of RCA 7591s makes a big difference. Tried the EHs but was a little disappointed, lost a lot of the sweetness.
Heard all of the NOS 7591s were made by RCA?
Actually all 7591 were made by westinghouse. They created this obscure tube. They may have contracted RCA to produce the tube but its a WH tube

My 2-225's have 8 WH 7591 black solid base hope they last my life time they are that good just like your RCA

As for the EH you tried they burn a little cooler than the old stock. You need to make a cap value change to accomidate the EH or they tend to glow bluish and burn up
Not sure what the values are but the JJ tubes are very tempermental with the MC225
Made the cap change alas no change in sound. The RCAs(Westinghouse) went back into action and still remain.
I don't own any new production tubes. Always been happy with old stock used or new The NOS 7591 tubes will last a lifetime just as long as they are biased properly.