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In Reply to: RE: Which version of the M60 do you have? It makes a difference. posted by jeffreybehr on March 26, 2017 at 11:47:34
I don't own an M60, but just from the 2 photos and from what Jeff said, I would guess that the middle rear tube of 3 is a CCS (Constant Current Source), solid state in a 3-tube 3.3 and tube-based in the 4-tube 3.1 version. The CCS does not have much effect on sonics per se, but the implementation can have an effect, which is to say that there is no need to use a boutique 6SN7 as a CCS. Two of the remaining three tubes, in a 4-tube input/driver stage, must therefore be in the dual-differential cascode topology. That's what does the work of voltage gain that drives the whole amplifier. Essentially, that's what you are hearing; the output tubes add little to no gain; they serve mainly to convert voltage to current. The remaining tube is a cathode follower, one half of each twin triode drives one half of the total of 8 output tubes. The CF takes the output from the cascode and reduces the net output impedance of the signal from the cascode so as to drive the output tubes. Both the dual-differential cascode AND the Cathode follower benefit from a CCS, so I don't know which one has a solid state CCS or if both do in the 3.3 version.
We phased out the 6SN7 CCS circuit with the Mk3.2. The new solid state CCS has an order of magnitude greater performance.
So the outside tubes are the bottom of the cascode, the middle rear is the top of the cascode and the front tube is the CF driver.
Thank you so much for the information.
So, here is what I am gathering for the M-60' Mk 3.3 version;
The best tubes should go at the 2 rear left and right positions. The rear middle position is not affected as much by the tube quality and therefore there is not much need to use (boutique Sophie)tubes in that position. Actually the Sophie's are wider and it would be impossible to fit 3 of them across the back row.
And the front center tube should be a 6SN7GTB per Ralph at Atma-sphere.
Does that sound like I got it?
You'd be much better off with facts from Ralph re what tube does what than conjecture from me. But the concepts are correct. I find it difficult to understand how the two outside tubes among the rear 3 (the tube on the far L and the tube on the far R) are together to form the dual-differential cascode, because those tubes are interconnected in a rather complex way, and I doubt that Atma would have them separated by the presence of the middle tube. It certainly could be the case, but I don't know for sure. That's why I suggest you ask Ralph.
By the way, what is a "Sophie" tube, and in what way are its dimensions different from a 6SN7GT, GTA, or GTB?
...to the Sophia 6SN7.
Tin-eared audiofool, large-scale-Classical music lover, and damned-amateur fotografer.
William Bruce Cameron: "...not everything that can be counted counts, and not everything that counts can be counted."
Took that quote from the Sophia website. It's an odd one, because CV32/33 and CV181 are in fact NOT 6SN7s in any way. I have seen CV181s, and they generally resemble those Sophia tubes being sold as 6SN7 replacements. They are electrically different from a 6SN7, and that's why they will sound different from a 6SN7 if plugged into a circuit designed for a 6SN7. On the other hand, CV1988 is a legitimate alternative name for a 6SN7. I have some Mullard/Brimar tubes that are labeled "6SN7GT/CV1988". I have no idea what Sophia is smoking.
The Sophie tube is an Audiophile tube that is taller and wider than the normal size 6SN7 tubes.
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