MC2301 Power Tubes & Driver Information (plus a MC275 V bonus)

[Dj_AmTraX]

I read somewhere that the 12AX7s in V1, V2, & V5 are the ones to change for improved performance on a Mc275 MKV. I am using Mullard reissued in those positions. Did I waste my money?

What about the Mc2000? Which ones are more bang for the buck?

[nsgarch]

Originally Posted by Dj_AmTraX

I read somewhere that the 12AX7s in V1, V2, & V5 are the ones to change for improved performance on a Mc275 MKV. I am using Mullard reissued in those positions. Did I waste my money?

No you didn't waste your money. I don't know anyting about 2301's but I know a lot about 275's and the information Bob posted about the 275 is incorrect. The 12AT7's, V-3,4 should match because (as a pair) they drive the KT88's V-8,9. Similarly V-6,7 (12AT7) drive V-10,11 (KT88.) Those two groups of four tubes (2AT's + 2KT's) are shown quite clearly on the Factory Schematics as I just noted: i.e. V-3,6 and V-4,7 do NOT work as pairs! The pairs of AT's are V-3,4 and V-6,7. Order a schematic and see for yourself. Nowhere are V-4,7 or V-3,6 even electrically connected -- not even their filaments!

Another tidbit I'd like to correct: if by significant were talking sonically significant, then clearly the two 12AX7 gain stage tubes (V-2,5) have the most affect on sonics in a 275, as I'm sure anyone who has rolled the three different kinds of tubes in a 275 will attest.

Sounds to me like maybe lunch involved a little too much alcohol

[Dj_AmTraX]

My 12AT7s in V3 & V6 are stock Mcintosh USA tubes. When I bought the Mullard 12AX7s I did not compare the sound against the stock tubes so I can't say if they sound better. Perhaps I should.

[vintage_tube]

Originally Posted by nsgarch

No you didn't waste your money. I don't know anyting about 2301's but I know a lot about 275's and the information Bob posted about the 275 is incorrect. The 12AT7's, V-3,4 should match because (as a pair) they drive the KT88's V-8,9. Similarly V-6,7 (12AT7) drive V-10,11 (KT88.) Those two groups of four tubes (2AT's + 2KT's) are shown quite clearly on the Factory Schematics as I just noted: i.e. V-3,6 and V-4,7 do NOT work as pairs! The pairs of AT's are V-3,4 and V-6,7. Order a schematic and see for yourself. Nowhere are V-4,7 or V-3,6 even electrically connected -- not even their filaments!

Another tidbit I'd like to correct: if by significant were talking sonically significant, then clearly the two 12AX7 gain stage tubes (V-2,5) have the most affect on sonics in a 275, as I'm sure anyone who has rolled the three different kinds of tubes in a 275 will attest.

Sounds to me like maybe lunch involved a little too much alcohol

Hi Neil,

As we've communicated several times in the past concerning tubes for MC275's I appreciated every tidbit you were willing to share and took many of your recommendations to heart. I valued and respected your input (and still do, by the way).

However, in this case you are absolutely off the pentode beam concerning the information in bold. V3 and V4 (and V6/V7) do not drive the plates & cathodes of the KT88's which you purport in posts. Infact, there isn't a McIntosh amp that was designed, nor developed, nor in use in which any 12v tube is used to drive the cathodes.

If you look at a schematic, it's easy to see how one could come to that conclusion that you do. The cathode to driver tube connection is actually performed using what McIntosh refers to as a bootstrap -- a form of cathode feedback to resistors in the path.

Secondly, to clarify a larger misnomer, McIntosh is able to squeeze 100 watts, or near that amount of wattage out of a pair of KT88's is because the output is taken from the plates and cathode and then applied in the unity coupling. The driver tubes only drive the plates as noted above.

So, I'll stand by what I reported as obtained from Ron Evans --a person who knows more about the MC275 than anyone on this forum will ever be able to comprehend.

In summary, V3 and V6 are significant and I'll concede with stating from Mr. Evans that V2 and V5 follow those in importance.

So, in closing, I didn't appreciate the lunch and alcohol comment -- next time -- just tell me I'm full of shi+. I appreciate frankness more so than bullshit.

I'll take my First Sergeant hat off now and get back to music.

Bob

[Formerly YB-2]

Wind-bag. For some reason that sobriquet comes to mind when reading the preceding post (not you, Bob).

And, I'll be putting my triode matched 12AT7s in V3 & V6 this weekend.

[W9TR]

Bob,
Thanks for the info - very helpful. I've been experimenting with 12AT7's because I can actually hear a difference when I change them out, and they don't break the bank, only 4 of them are needed. I'm now running NOS Mullards. Much better to my ears than the stock tubes. So your post clarified that for me. Awesome. Did Ron Evans comment about trying to find high transconductance examples, or was he just focused on matching?

[Mctwins]

Hi
If one does not have a tube tester, how will I now that the two tube is matched even if I buy matched pairs. One can never be certain that it is correct.

How will I know or find these parameters?
What is the tolerance?

**What's critical for amplifier performance is based on two designs of the unity coupled output:
a. How well matched the idle current is on the right and left power tube banks.
b. The maximum cathode and plate current capabilities.

Thanks

[nsgarch]

Originally Posted by vintage_tube

If you look at a schematic, it's easy to see how one could come to that conclusion that you do. The cathode to driver tube connection is actually performed using what McIntosh refers to as a bootstrap -- a form of cathode feedback to resistors in the path.

Bob, looking at a schematic of an MC275 -- it would be obvious to the most casual observer that V-2,3,4,8, and 9, are all part of the left channel circuitry and do not (because they must not) have any connection to V-5,6,7,10, and 11. If those two groups were ever connected in some way, you would certainly not get stereo! They also remain separate circuits in the mono mode as well, until their outputs are connected by a jumper at the speaker taps.

Secondly, to clarify a larger misnomer, McIntosh is able to squeeze 100 watts, or near that amount of wattage out of a pair of KT88's is because the output is taken from the plates and cathode and then applied in the unity coupling.

That's true, I don't know what the "larger misnomer" is you mention. However, to be more specific, power is taken separately from the plate and from the cathode and fed separately to one of two separate but parallel (bifilar) primary windings on the output transformer. The "Unity Coupling" actually occurs in the transformer, and wouldn't occur if the two primary windings weren't laid down parallel turn by turn.

The driver tubes only drive the plates as noted above.

Tubes are "driven" by other tubes. Plates are not "driven". A "driver" tube (in an amplifier) is customarily the tube (the 12AT7 in a 275) that controls the voltage of the grid(s) in the power tube. The grid voltage in the power tube allows (a large) current to pass (or not) to the plates, which, through the output transformer, drives the loudspeaker. Plates are not driven, by anything. They simply complete current flow through the tube when the grid voltage allows it to flow.

So, I'll stand by what I reported as obtained from Ron Evans --a person who knows more about the MC275 than anyone on this forum will ever be able to comprehend.

Look, Bob; I wasn't there, and I don't know what the boys from Binghampton said, but I know what you thought they said; so the "lunch and alcohol" remark was directed at them, not at you. You are more than welcome to share my response with them.

Neil

[Jerome W]

WOOOOOH....................

I read all theses posts and now I need an Aspirin !

Thinking about all these tubes in the 2301, it would surely have been less trouble to buy a pair of 1.2KWs, but I would get Maybe a less charming sound..... ( Jim, don't jump on this one, I said MAYBE ! )

Jerome

[Still-One]

Originally Posted by C220MC275

WOOOOOH....................

I read all theses posts and now I need an Aspirin !

Thinking about all these tubes in the 2301, it would surely have been less trouble to buy a pair of 1.2KWs, but I would get Maybe a less charming sound..... ( Jim, don't jump on this one, I said MAYBE ! )

Jerome

Jerome, Hey, I am just lurking here. This thread is way over my head.

Jim