Rolling with McIntosh 275

Tube rolling with MC could be a lot of fun and could lead to a sound that you will not only like, but love. The flexibility is just incredible. This post will focus only on preamp tubes. Power tubes are out-of-scope πŸ™‚

There are 7 preamp tubes in reissue MC 275, V1 (12ax7) – phase-splitter, V2, V5 (12ax7) – input amplifiers. V3, V6 (12at7) – output tube drivers, V4, V7 (12at7) – Cathode followers.

First of all, if you are using balanced inputs, you can forget about V1. It’s not used by the amp. However, keep it in. It’s in the heater chain with the other tubes (since MC uses 24v for heaters), so removing it will remove a part of the heater circuit. But place there something cheap. It doesn’t even have to be 12ax7 – you can place GE 12au7 there with the same results and invest your money in the other tubes. On the other hand, if you use unbalanced input – V1 is one of the most interesting tubes to play with and produces some very unexpected and in some cases phenomenal results due to the circuit design.
First, let’s get the 12at7 tubes out of the way. Use good tubes there. Grey plates work better than the majority of black plates (I can’t believe I just said that) – because they are more transparent. Try to use old stock – they have sweeter HF. You need a tube with a lot of transparency and great sound-stage. Telefunkens would work, but expensive. Sylvania 12at7 Gold Brand is much cheaper and works as well. (see my previous post on 12at7s) One interesting result I was able to achieve is with 12av7 and 7062 tubes. Sound stage was just out of the is world! Try to stay with the same type in the chain, but no harm in going with different types for Driver & Cathode Follower. I have Sylvania JHS 12at7 as a driver and Amperex 7062 as Cathode Follower and love the results – your results might vary. So again, save your money and focus on 12ax7 tubes.

About V1. The design of the phase-splitter is quite unconventional since the amp is fully balanced from balanced inputs through the power tubes, but uses V1 to invert the signal before passing it on into the balanced chain. However, it uses 1/2 of the dual triode for each channel for the negative phase and feeds positive phase as is into the input stage. This could create time delays – depending on the tube. So rolling different tubes in V1 could result not only in different tone, but also in a time delay – which is quite an experience when part of the signal is unchanged and the other part, negative phase, is delayed – opens up a new dimension into the music!!!

V2 & V5 are a more conventional design of the input stage of voltage amplifier and thus could be very efficiently used to roll tubes with fantastic or horrific results.There are a lot of reviews on this site that talk about results of the rolling – read up! πŸ™‚

About tube matching… There is not much need to match input tubes. V1 is completely independent of the other tubes – and although matching triodes could lead to a potential benefit, it’s very likely to be unnoticeable. V2 & V5 don’t have to be matched either because of the deep negative feedback loop that would eliminate the majority of variances and could leave you with 1-3% of difference that is practically impossible to hear. So don’t waist your money on matching. The independent feedback control inside of each phase pipe would also dramatically reduce theΒ  triode differences. The amp is very forgiving.

Roll on!!! Post your experiences on this site.

3 thoughts on “Rolling with McIntosh 275

  1. Hi, this is a relly good piece of knowledge about tube rolling for Mc275.
    I have used this for first setup and then slightly modify for the best effect.
    V1, V2 and V5 are Telefunken Smooth Plates 12AX7
    V3, V4 are Mullard 12AT7
    V6, V7 are Telefunken 12AT7
    With Mullards on V3 and V4 noticed better bass and oveall more vinitage sound (bit smoother and deeper) comparing to Tele.
    I will probably have a second MC275 next days so will use both in MONO mode.
    Is there any additional suggestion for tubes in case of switching to MONO mode ?
    Would be happy to hear your recommendations, if any
    regards
    Darek (dwk1965)

  2. need to correct my message /misplaced tubes position in previous log
    V1, V2 and V5 are Telefunken Smooth Plates 12AX7
    V3, V6 are Mullard 12AT7
    V4, V7 are Telefunken 12AT7

  3. Although I think your explanation works for versions Mk IV and earlier MC275s I’m concerned your explanation of the role of the various tubes in “reissue MC275’s” could be misleading to some. The reissue MC275 you can buy now and for the last several years is the MK VI. The MK VI has completely different tube numbering than the earlier 275’s. It also has a different circuit than the earlier amps. I own a MK VI, its service manual and schematic. I’ve also been into the amp and made modifications. The Mk VI phase splitter tube is V4. And it is not in the circuit at all when using unbalanced (RCA) interconnects. Only when using balanced (XLR) interconnects does the signal pass thru V4. Also, have you experienced any problem or any excessive xformer heat when using the 7062 tubes in the MC275? I believe their heaters pull 50 additional milliamps than an 12AT7.

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