Phono preamp tube rolling.

Tube Rolling is a great experience.
Learning how certain Brands and Production Era's interface in a circuit and deliver into the Downstream of the System is a something that is worthwhile undertaking.

Trusting the Supplied Tubes is the issue.
I have come to terms with the fact that Tubes will make music happen, and to the inexperienced such as myself, I would not know whether one is of the ideal measurement.
An asking price from a Vendor can suggest it is Factory Spec and certain supplied measurements will suggest the Tube is Factory Spec.
Give such a Tube to a Time Served Valve Individual with Testing Kit  and a full knowledge of testing and the supplied Tube can be proven to fall short of the Factory Spec by quite a margin.

I only purchase Tubes today that come with the right to return if a secondary measuring  at my end does not match the vendors advertisement.

I have returned Tubes for the above reason, both  NOS and New.   

As a result of being vigilant with a purchase, I have Vintage Tubes in a DAC, Phon, and Power Amp.
I have selected these over New Tubes as a result of Tube Rolling experiences. 

The Impact of an SUT or Head Amp on the downstream of the system can be just as impressive as a change to a certain Tube can offer.  

When I Tube Rolled 6SN7 and Variants of this Tube.
I did this without support or loans of tubes from experienced owners.

In comparison to other Tube Rolling experiences, it proved to be the most difficult to make a selection, as some tubes choices, once with a little run time sounded like competitors to go on to a Short List.

When longer evaluation periods were used for the tubes, certain tubes became very different in their SQ and had to be removed, as the deterioration was very obvious.
There was a concern that the tube was developing a fault. 

I would say best to stick close to the advice of others with worthwhile experience as the selection for the initial investigations.
A Benchmark can be set for any other experiences to be had down the line.

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. 

  

The 6SN7 Tubes I have retained for use are Kenrad VT231 Black Glass and a Sylvania GT Tube.
These are different in their presentation as an interface where they the input Tubes on 845 Monoblock Power Amp’s.

I would very much like to try other Vintage, and will most likely return to this when the Mono’s are converted to a Balanced Design.

Absolutely Correct about the ECC33, hence the advice given to myself to discuss this Tube with the 845 Designer/Builder.

It was Jaw on the Floor when the KenRad's were put into service.  
The KenRads and Sylvanias are both fine for ESL Speakers in my system.
The Sylvanias are a little too rich for my my tastes when used and the  Floor Standing Cabinet Speakers are in use.   

My 845 Mono's Input design is a little unusual as it has certain Tubes in Pairs that are only using Half of the Tube in the Circuit.
There is only One 6SN7 Per Monoblock and these are only using Half of the Tube in the Circuit.
It is always difficult to explain a Bespoke Built Design for the SQ, there is a separation in SQ and usually the only way to fully comprehend the designs capabilities is to be in the room with it.

Totally agree about a Cap' change having a profound effect.
The Phonostage I am using has been auditioned in various circuits for the end design to be produced.
When the prototype was almost complete and identified as being a very attractive performer.
Curiosity was still with myself and a couple of Cap' and Resistor changes were encouraged to be undertaken that had been discussed and not as yet trialled.
A Brand change of a Copper Cap with a different value and a few Z Foils was a remarkable change and the one I have maintained in my owned model.