Phono preamp tube rolling.

I have a Zestos Andros Deluxe 2 that I've done a fair amount of tube rolling in.  The Zestos has two 12AX7s in the "primary" spot, and an interesting pair of 12DW7s (one triode has an 12au7 like mu, the other having a 12Ax7 like higher mu), which according to Zestos drive the dedicated output transformers.  I've rolled both positions, the 12 DW7 makes only a slight difference in clarity.  I've tried Mullard 12DW7s, some American NOS ones... not much difference to be honest.  I put in some NOS Orion DW7s (made by Tungsram) cause they look the coolest and I convinced myself they sound the best.  : ) 

The 12AX7s do make a pronounced sonic difference though.  In lieu on the stock JJs,  I've tried several NOS including: Telefunken smooth plates, Tunsgram 12AX7, RCA black plates, Mullard longplate square getters, Amperex long plates D getters, and Tesla E83CCs.  Long story short, the best sound came from the Teslas and the Telefunken in terms of clarity, bandwidth and detail.  Close behind were the Tunsgrams, which although deviating from neutral, had a seductive bloom to them.  The RCA black plates fared surprisingly well with a punch and clarity that I could've lived with.  The Mullards sounded like a wet blanket over the speakers, and were not suited for this phono amp usage.  All tubes were very quiet.  I'm leaving in the Teslas.  BTW, I love this phono amp.  It frankly far surpasses the Pass XP15 that preceded it in all areas.  The Zestos is completely quiet, with no overt tube noise.  It's end game for me.

gakerty
Mullards have never lasted too long in a phono stage or any other application here, for the reason you colorfully cite :)

The Zestos looks lovely and its use of an asymmetric dual-triode is very interesting! Use of output transformers is cool, too. I'd love to hear one some day. 

Certain Tubes can be quite expensive and tube rolling can generate a considerable outlay for the items to be compared.
I shared the pitfalls I had with the 6SN7 when I went alone on the subject of rolling these.
I have 5 out of Seven Pairs of NOS and New 6SN7 Tubes that are rejected.
A few of these pairs I will not sell on as they are not something I would like another to experience, I have no intention to reproduce the stress and the concern the use of them can inflect.

My later experiences where support from experienced individuals was at hand and the offer to assist accepted proved to be much more successful, and the choices made by myself have been keepers.

Ironically two friends that were consulted with,  for advice on other Tube Models are also agreeing and promoting the same 6SN7 I have chosen as their preferred tube.
One friend also thinks I am with a very good 6SN7 Tube and would like me to try the ECC33 once I have the approval of the Power Amp's Designer/Engineer to use it. 
The ECC33 was a Tube I was not even considering. 

  

mulveling-- Those Mullards, despite their lore and hype, have never really found favor for me, either as gain tube in my Rogue ST100, nor here in the Zestos. I paid a fair amount for them, and really wanted to like them, but I suppose my ears and system don’t really need to be fattened up by the Mullards. : ) If I need thickening, the RCA black plate will achieve that, with no compromise on bandwidth.

I am indeed smitten with the Zestos, but it is my first tube phono amp, so I am new at phono tubes. It is just beautiful all around. I got a good deal on it here at Agon and jumped on it. I’m REALLY glad I did. Insert your audiophile cliches here: "veils lifted...." etc. : )

Another great and cheap alternative (NOS) for me was the Sylvania 12at7WA

Sylvania Gold Brand 12AT7WA is a high-frequency twin triode in a small 9-pin miniature glass package. This is a very rare military gold pins version from the 60’s, made in the USA. The 12AT7WA is found in many high fidelity applications, as each triode section in normal use operates as a class A amplifier. This tube is very low in microphonics due to its rugged construction. Sylvania Gold Brand is an extremely high demand vintage tube. Sylvania was a U.S. manufacturer of vacuum tubes, transistors and electrical equipment, formed in 1931. Their vacuum tubes from the 50’s and 60’s (Gold Brand series) are very nice!