Recommended 12au7/5814s for Atma-sphere MP-3

I have Herbies on every tube for good measure. I did spring for the RCA GT (Grey Glass - 1940s)that are suppose to be very well matched and I'm keeping my fingers crossed, quiet. I think I'm going to stick with Sylvania early GTBs for the M-60s, though I might roll some GTs in putting them into the mix helps. Is everyone in agreement that GT/231s (assuming they are quiet and well matched sections) generally sound better than GTA/Bs?

I haven't done much rolling with my MP-1, but I'm using a Raytheon 6SN7 in the forward position(differential amplifier where all LS gain is performed), a matched pair of 6SN7EH in the circlotron, and 6SN7EH in CCS. IMO the latest EH production sounds clear, extended, & musical. The front 6SN7 is a good place to experiment with NOS tonality. In the phono section Mullard 12AT7(selected for low noise by Jim Mcshane), improvement upon the stock Chinese tubes both in quietness & sonics. The first two 12AT7s in the phono section circuit are in parallel, forming together the top half of a cascode with the third tube. When rolling the phono stage, you would probably want to replace the first two 12AT7s with the same type of low-noise NOS tube.

Jtimothya, great reading on that link. Thanks.

When rolling the phono stage, you would probably want to replace the first two 12AT7s with the same type of low-noise NOS tube.
Dgarretson (System | Threads | Answers)

This is not clear to me. Which position do you consider the first two?

In the MP-1, starting from the rear, the 1st two positions are wired differentially within a tube and the 2 tubes are then in parallel. This is the bottom of the cascode. The 3rd tube is the top of the cascode. So the 1st two make the most difference.

In the MP-3, the 1st tube from the rear is the bottom of the cascode differential, and the 2nd tube is the top.

Generally speaking the noise importance of the tubes decreases as the signal progresses from the rear to the front of the unit, but that is not to say that the final tube is not sensitive to noise.

Generally we advise people to stay away from NOS in the phono section because of tube aging. In this case, not the NOS tubes, but the OEM tube, which is Chinese. Unless those tubes are new, they will be noisier than they should, so often NOS tubes replace them, and then the preamp gets accused of being noisy when really what is happening is the NOS tubes, while being quieter than the OEM tube (which might have gone down hill its own self), are still not quiet *enough*.

That is not to say that you can't find NOS tubes that *are* quiet, but they are rare these days.