• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MC-240 Tube Rolling Questions

MrPoetry said:
New listening information:

TL;DR
  • Listened to a Mullard I61 (1963) in the MC240’s V1
  • Adored the lush mids and gorgeous tone
  • Did not like:
    - effects of recessed presence: impact & excitement that I'm used to (with a JJ ARS in V1) were gone
    - the famous Mullard liquidity was slightly too syrupy, and bass was heavy handed
  • Hypothesis:
    - Denafrips Pontus R2R + AN UK M3 + MC240 already combine to add Mullard-ish sonics, creating these overdone-warmth effects
    - Any glare from Klipsch Heresys can & should be addressed by direct treatment (e.g. new ALK crossovers, etc.) rather than MC240’s tubes
  • NEW QUESTION: Can Mullard beauty be included in a signal tube lineup by combining it with, say, Telefunken, in order to restore presence and musical excitement?

The Full Story

I received the Mullard I ordered, but it was the wrong Mullard: I ordered 1950s; received 1963 (model I61). Andy B. encouraged me to listen to it, to see if I wanted to keep it. I’m going to return it, but I have been strategically listening to specific musical passages with the 1963 Mullard in V1, to hear how it’s affecting the sound. Here is a summary of my listening notes:
  • I LOVE the Mullard-added rich tonality, especially vocals, and, for example, the viola in a Beethoven Quartet. I’m hearing the famous lush midrange, and I love it.
  • Violins sound tamer, but at volume (e.g. in a Brahms symphony) still sound harsh. This harshness sounds more distinctly like the Heresys; i.e. the better harmonics of the Mullard are, in contrast to everything else sounding simply gorgeous, differentiating the Heresys’ negative contribution. In other words, the Mullard is having a mitigating effect, but not curing a downstream problem in the speakers -- which feels like an unfair and perhaps unwise job to saddle the tubes with.
  • I’m hearing too much of the Mullard’s good things, and missing presence that I had before. Specifically, the liquidity does sound a little too syrupy; the bass feels beautiful but overdressed, less impactful, and a little smothering; snap, slam, bowing the strings and striking the piano keys are all diminished to the point that I can sometimes hear them at a distance, but can no longer feel them.
In short, there is more exquisite beauty, but less sexiness. The excitement is pretty much gone.

Question: Is it possible to separate my tube selection criteria from the Heresys’ glare, considering that the new ALK Crossovers I ordered will arrive eventually? The ALKs might go a long way to solving that particular problem: they cross over more precisely (not, as the original stock xovers do, by generously sharing the 6kHz-8kHz range), and they’ll let me attenuate both squawker and tweeter gain.

Moreover, I’m wondering if the trio Denafrips R2R (described by one reviewer as “dark”) + AN UK M3 + MC240 is too prone to the Mullard’s charms. On the other hand the sounds that I’m loving are clearly being added by the Mullard; but I think I might be discovering that those charms are already more at play than I was aware of in this organic, analogue-sounding trio of components.

Now, the V1 I had in the MC240 before the Mullard is a JJ ARS (chosen and put in for me in 1994 by a knowledgeable tube tech who was adhering to my severely limited budget at the time). It has a lot of excitement, but far less complexity and beauty than the Mullard.

In my tube-inexperienced simple mind, I’m thinking: Oo oo! couldn’t I combine Telefunken and Mullard to get the best of both their worlds? -- But please bear in mind that (a) as far as I know I’ve never heard a Telefunken tube in action, nor any other high quality NOS signal tubes; and (b) this thought is my wishful thinking. In the best of all possible worlds, what I’ve heard in this 1963 Mullard + what I’ve read about NOS Telefunken is what I imagine I want to hear.

With an MC1 in V1, can other tubes bring back the presence-based excitement? Or with a Telefunken (or other?) tube in V1, can matched Mullards (or are there equivalents?) contribute the qualities I’m loving in ways I’ll be able to hear, without over-damping the other tube’s presence?
Click to expand...
Sell the Mc240 and get a properly restored Mc225. Same circuit, one less gain stage. Use a Telefunken EC83 as V1 and be done with it.
 
ramjet said:
Sell the Mc240 and get a properly restored Mc225. Same circuit, one less gain stage. Use a Telefunken EC83 as V1
Click to expand...
@ramjet I'm intrigued by the implications of this. Not at a point where I'm considering selling the gift from my father, but would you be willing to share your underlying logic? -- The one more gain stage in the MC240 are V4 & V7, the ECC83 cathode followers; how is this extra gain stage (compared with MC225) affecting the sound?

I'm also interested in what you particularly like about the Telefunken in the MC225.
 
MrPoetry said:
@ramjet I'm intrigued by the implications of this. Not at a point where I'm considering selling the gift from my father, but would you be willing to share your underlying logic? -- The one more gain stage in the MC240 are V4 & V7, the ECC83 cathode followers; how is this extra gain stage (compared with MC225) affecting the sound?

I'm also interested in what you particularly like about the Telefunken in the MC225.
Click to expand...
Full disclosure but I have never listened to a MC240. I have restored two Mc225s, two Mc60s and have listened to Mc40s and Mc275s. I own a Mc225, Marantz 8 and HK Citation V amplifiers, all restored. I use the Mc225 daily. Many on this forum, myself included, have stated their preference for the Mc225 "sound" (if there is such a thing) over many other tube amplifiers. The criticism has been that it lacks power. That's a speaker issue.
The one less stage means less distortion (every stage adds). I choose the Telefunken not because of a "sound" but because I have found through 55+ plus years of vacuum tube experience that the measurable qualities of this tube brand (distortion, section balance, lifespan, etc) are consistent sample over sample.
 
cicada_shell said:
Telling someone to sell the most popular classic Mac stereo amp produced despite having never listened to it based on forum hearsay is very bold.
Click to expand...

I try not to weigh in on tube amp discussions too much, it’s like discussing religion.

I owned a very nice late-late MC240, among other tube amps, it did sound delightful. I rolled many tubes through it from modern JJ and TS to NOS RCA, Telefunken 12AX7A and Mullard, the “clear-top” (organ) RCAs, … other than the new-issue TS tubes I really didn’t hear anything that I didn’t like.

My wife loved that amp, told me that there was a shrillness in other amps that the 240 didn’t have. I tried to trick her a couple of times by swapping in different amps, she always caught it before even sitting down, so I know there is a difference that affects some people more.

But I’m a Solid-State guy, want pure and un-distorted, so I only have my remaining tube amps (MC75s) for her, daily is SS.

So how does one decide that the MC225 is better, with its different topology and a softer (tube rectified) power supply that can’t quite deliver the punch of more evolved amplifiers and SS? It’s distortion, the only thing that tubes can bring to the table, it’s soft-clipping of bass punch, it’s the altered/distorted sound and harmonics that Bob Carver was able to measure and duplicate in the Bob Carver Challenge and emulate in the “Transfer Function” series of amplifiers.

So if some prefer a softer power supply, many seem to almost to a legendary status here on AK, the earlier tube-rectified amplifiers are better. Others will argue that the MC225 is too evolved, and a simpler “single-ended” amplifier will even better change the music for a more pleasant sound, complicated topologies such as the MC225 and *gasp* a later MC275 would certainly not be listenable.

There is absolutely nothing wrong with the design and music from the MC240, in fact I’ll argue that McIntosh Engineers developed it to replace the MC225 for reasons other than simple power output (as they had the MC275 for that), and it is a more accurate amplifier than its predecessor. If the hippocratic oath can be paraphrased and used in music reproduction: “First do no harm” applies in my audio world, choose that with less alteration to the sound (which is why Solid State for me). However music being art, music reproduction being science, one may choose to view (audition) one’s art through whatever lens makes it most pleasant, and my wife’s lens would be the MC240, and I will argue that the only modern output tubes that were reasonably listenable were the JJs, vintage tubes were noticeably better. Small tubes varied, I didn’t like modern in the 12AX7A slot, didn’t like the “clear top”, but otherwise differences were minor enough for me to not hear it (nor was I interested in the time involved in swapping back and forth enough times to try and find a difference).
 
Per the MC225 manual, it has a silicon power supply rectifier.

And per my memory, it appeared after the 240 by a couple of months but they were more or less released at the same time. The 225 was perceived as a budget option in the lineup and was about 30-40% cheaper. I believe about 1/3 the units were sold compared to the 240, as well. I posted the figures in my McIntosh production figures thread in this sub forum, source being the McIntosh Compendium.

After having heard them all, they all sound about the same when used with an appropriate speaker. They are all good amps.
 
SaturationPt said:
I try not to weigh in on tube amp discussions too much, it’s like discussing religion.

I owned a very nice late-late MC240, among other tube amps, it did sound delightful. I rolled many tubes through it from modern JJ and TS to NOS RCA, Telefunken 12AX7A and Mullard, the “clear-top” (organ) RCAs, … other than the new-issue TS tubes I really didn’t hear anything that I didn’t like.

My wife loved that amp, told me that there was a shrillness in other amps that the 240 didn’t have. I tried to trick her a couple of times by swapping in different amps, she always caught it before even sitting down, so I know there is a difference that affects some people more.

But I’m a Solid-State guy, want pure and un-distorted, so I only have my remaining tube amps (MC75s) for her, daily is SS.

So how does one decide that the MC225 is better, with its different topology and a softer (tube rectified) power supply that can’t quite deliver the punch of more evolved amplifiers and SS? It’s distortion, the only thing that tubes can bring to the table, it’s soft-clipping of bass punch, it’s the altered/distorted sound and harmonics that Bob Carver was able to measure and duplicate in the Bob Carver Challenge and emulate in the “Transfer Function” series of amplifiers.

So if some prefer a softer power supply, many seem to almost to a legendary status here on AK, the earlier tube-rectified amplifiers are better. Others will argue that the MC225 is too evolved, and a simpler “single-ended” amplifier will even better change the music for a more pleasant sound, complicated topologies such as the MC225 and *gasp* a later MC275 would certainly not be listenable.

There is absolutely nothing wrong with the design and music from the MC240, in fact I’ll argue that McIntosh Engineers developed it to replace the MC225 for reasons other than simple power output (as they had the MC275 for that), and it is a more accurate amplifier than its predecessor. If the hippocratic oath can be paraphrased and used in music reproduction: “First do no harm” applies in my audio world, choose that with less alteration to the sound (which is why Solid State for me). However music being art, music reproduction being science, one may choose to view (audition) one’s art through whatever lens makes it most pleasant, and my wife’s lens would be the MC240, and I will argue that the only modern output tubes that were reasonably listenable were the JJs, vintage tubes were noticeably better. Small tubes varied, I didn’t like modern in the 12AX7A slot, didn’t like the “clear top”, but otherwise differences were minor enough for me to not hear it (nor was I interested in the time involved in swapping back and forth enough times to try and find a difference).
Click to expand...
The Mc225 has a solid state voltage doubler power supply, same as the Mc240. If we can trust "The McIntosh Compendium", the Mc240 came out in July, 1960, and the Mc225 came out in June, 1961.
 
My bad, I thought that the MC225 was MC30/MC60 era, but it was not (never had one, came of age during the MC2105’s time). Tube amps were cheap then, I’m not sure that Mc dealers were even taking them on trade-in anymore as the second SS generation was already available. I was able to get two mono amps for free (from two different people), dealer didn’t want them.
 
sberger said:
My 240 sounds every bit as good as my 225. And they both as good as my MC30's.

Agree 100%
Click to expand...
No 225 here but I do have a 240 and use to own a pr of mc30's and it's definitely as good as the mc30's I had.I plan on doing some tube rolling with some nos tubes I have on hand but I really don't have golden ears so we will see if I can notice a difference
.
 
Update:

I developed a nagging hunch that maybe my priority should be tubing the Mc240 such that the qualities of the Audio Note M3 could shine through as clearly as possible. I followed that hunch, bit the bullet and ordered a matched pair of ANOS Telefunken ECC83's (w/balanced triodes) from Doug Preston (Doug's Tubes), thinking I'd try one in V1, and if I ended up getting a Mullard for V1, I could use the Teles in V4/V7.
ramjet said:
Use a Telefunken EC83 as V1 and be done with it
Click to expand...
The Telefunken in V1 is a revelation. I won't go on about its well known qualities; there is a good description here, which I'm finding completely accurate. The surprising reveals are:
  • Contrary to my worries that glare from the Klipsch and somewhat live room acoustics would be reproduced mercilessly, the Telefunken is so smooth, clean and transparent that it virtually eliminated those problems.
  • My hunch about letting the M3's sound signature through was right: the music sounds gorgeous and involving, and all the presence & excitement are there, even more so than with the JJ.
Telefunken will stay in V1. However, I am not done.

I continued my quest to find out how the other three tube circuits (V2/V5: 12AU7; V3/V6: 12BH7; V4/V7: 12AX7) affect the sonics, in order to know which tubes to prioritize. I will share here what I've found out; please comment on anything that follows that is off base or dead wrong. Confirming anything that is accurate is also helpful. I formed the following hypothesis by asking Chat GPT questions, giving GPT's answers to Claude to critique (and boy, good thing they're not married), searching for evidence to fill in the gaps Claude found, and having Claude explain the engineering that I don't know. Here are the results:
  • After V1, the 12BH7 tubes in V3/V6 should have the next greatest impact on the sound quality, based (Claude explained) on their job of swinging comparatively large voltages to the output grids. Whatever design/build characteristics these tubes impart get passed transparently through the cathode followers (a buffer stage with voltage gain just shy of unity), to the output tubes. It occurs to me that V3/V6's impact on sound quality might be a kind of analogous subset of V1's global impact: Just as V1's characteristics become baseline for all the downstream tube stages, so V3/V6's drive amplifier characteristics (including their inheritance from, hence a subset of V1) provide the baseline for the output stage.
  • The 12AU7 tubes in V2/V5 have more limited, more specific effects: (1) better or worse low-level detail, which depends on how well the triodes are balanced; and (2) treble tweaking, which results from an interaction with the next stage's drive amplifiers.
    1. Low-level detail: As @ramjet & @prww taught me earlier, the better the triodes are balanced, the less distortion. In the case of the phase splitters, the more exactly the equal & opposite the split signals are, the better they end up canceling "even-order harmonics" (whatever that means), which contributes to a lower noise floor, therefore blacker background, and therefore more low-level detail.
    2. Treble tweaking: I found a quote attributed to Steve Hoffman in which he suggested rolling the 12AU7 phase splitter to compensate for bright/forward or dark/recessed speakers. (He was reporting this on MC30s, but the MC30 schematic shows the same progression of tube stages as the MC240, so his claim should apply here.) I asked the AI department why the phase splitters would affect high end but not midrange or bass. Claude's conclusion: While a matched pair of 12AU7s' relative linearity/distortion of course could affect all bands, a more specific interaction takes place between the 12AU7 phase splitters and the 12BH7 drive amplifiers in the next stage: The 12AU7s' output impedance interacts with the capacitance of the 12BH7 drive amplifiers, such that: "output impedance × following-stage capacitance = RC low-pass filter." If I understand this correctly (I asked follow-up questions), the `=` sign in that quote means create: the 12AU7's output impedance x the 12BH7's capacitance creates an RC low-pass filter. The low-pass filter is the resulting effect of the phase splitter tubes' individual characteristics (beyond dual-triode balance) on the next stage, while all other frequencies (mids & bass) pass through the 12AU7 to the 12BH7 with no coloration. The created RC low-pass filter is half-shaped by the 12AU7 tube's characteristics (in combination with the 12BH7's capacitance); hence the treble tweaking effect. Therefore (as far as I can reason) the 12AU7 phase splitter's "treble-tweaking character" is a function of its output impedance.
  • The 12AX7 tubes in V4/V7 should have minimal impact on sonics. Any individual tube's "nonlinearities get divided down by a feedback factor" of 1+µ, which in a 12AX7 should result in a feedback suppression factor of about 100. The way I'm understanding this in context is that, while the drive amplifiers are driving the output grids, the cathode followers are providing a transparent buffer for the signal to get from the previous stage (the 12BH7s) to the next (the output tubes).
I'll pause here, and solicit your feedback. I want to find out how sound the above reasoning is, before moving on to possible choices for each remaining tube stage.
 
Last edited:
MrPoetry said:
Update:

I developed a nagging hunch that maybe my priority should be tubing the Mc240 such that the qualities of the Audio Note M3 could shine through as clearly as possible. I followed that hunch, bit the bullet and ordered a matched pair of ANOS Telefunken ECC83's (w/balanced triodes) from Doug Preston (Doug's Tubes), thinking I'd try one in V1, and if I ended up getting a Mullard for V1, I could use the Teles in V4/V7.

The Telefunken in V1 is a revelation. I won't go on about its well known qualities; there is a good description here, which I'm finding completely accurate. The surprising reveals are:
  • Contrary to my worries that glare from the Klipsch and somewhat live room acoustics would be reproduced mercilessly, the Telefunken is so smooth, clean and transparent that it virtually eliminated those problems.
  • My hunch about letting the M3's sound signature through was right: the music sounds gorgeous and involving, and all the presence & excitement are there, even more so than with the JJ.
Telefunken will stay in V1. However, I am not done.

I continued my quest to find out how the other three tube circuits (V2/V5: 12AU7; V3/V6: 12BH7; V4/V7: 12AX7) affect the sonics, in order to know which tubes to prioritize. I will share here what I've found out; please comment on anything that follows that is off base or dead wrong. Confirming anything that is accurate is also helpful. I formed the following hypothesis by asking Chat GPT questions, giving GPT's answers to Claude to critique (and boy, good thing they're not married), searching for evidence to fill in the gaps Claude found, and having Claude explain the engineering that I don't know. Here are the results:
  • After V1, the 12BH7 tubes in V3/V6 should have the next greatest impact on the sound quality, based (Claude explained) on their job of swinging comparatively large voltages to the output grids. Whatever design/build characteristics these tubes impart get passed transparently through the cathode followers (a buffer stage with voltage gain just shy of unity), to the output tubes. It occurs to me that V3/V6's impact on sound quality might be a kind of analogous subset of V1's global impact: Just as V1's characteristics become baseline for all the downstream tube stages, so V3/V6's drive amplifier characteristics (including their inheritance from, hence a subset of V1) provide the baseline for the output stage.
  • The 12AU7 tubes in V2/V5 have more limited, more specific effects: (1) better or worse low-level detail, which depends on how well the triodes are balanced; and (2) treble tweaking, which results from an interaction with the next stage's drive amplifiers.
    1. Low-level detail: As @ramjet & @prww taught me earlier, the better the triodes are balanced, the less distortion. In the case of the phase splitters, the more exactly the equal & opposite the split signals are, the better they end up canceling "even-order harmonics" (whatever that means), which contributes to a lower noise floor, therefore blacker background, and therefore more low-level detail.
    2. Treble tweaking: I found a quote attributed to Steve Hoffman in which he suggested rolling the 12AU7 phase splitter to compensate for bright/forward or dark/recessed speakers. (He was reporting this on MC30s, but the MC30 schematic shows the same progression of tube stages as the MC240, so his claim should apply here.) I asked the AI department why the phase splitters would affect high end but not midrange or bass. Claude's conclusion: While a matched pair of 12AU7s' relative linearity/distortion of course could affect all bands, a more specific interaction takes place between the 12AU7 phase splitters and the 12BH7 drive amplifiers in the next stage: The 12AU7s' output impedance interacts with the capacitance of the 12BH7 drive amplifiers, such that: "output impedance × following-stage capacitance = RC low-pass filter." If I understand this correctly (I asked follow-up questions), the `=` sign in that quote means create: the 12AU7's output impedance x the 12BH7's capacitance creates an RC low-pass filter. The low-pass filter is the resulting effect of the phase splitter tubes' individual characteristics (beyond dual-triode balance) on the next stage, while all other frequencies (mids & bass) pass through the 12AU7 to the 12BH7 with no coloration. The created RC low-pass filter is half-shaped by the 12AU7 tube's characteristics (in combination with the 12BH7's capacitance); hence the treble tweaking effect. Therefore (as far as I can reason) the 12AU7 phase splitter's "treble-tweaking character" is a function of its output impedance.
  • The 12AX7 tubes in V4/V7 should have minimal impact on sonics. Any individual tube's "nonlinearities get divided down by a feedback factor" of 1+µ, which in a 12AX7 should result in a feedback suppression factor of about 100. The way I'm understanding this in context is that, while the drive amplifiers are driving the output grids, the cathode followers are providing a transparent buffer for the signal to get from the previous stage (the 12BH7s) to the next (the output tubes).
I'll pause here, and solicit your feedback. I want to find out how sound the above reasoning is, before moving on to possible choices for each remaining tube stage.
Click to expand...
This: https://audiokarma.org/forums/threa...-from-an-iconic-design.1091907/#post-17931683
 
You must log in or register to reply here.
Back
Top Bottom