Phono preamp tube rolling.

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.   

@pindar. I've paired a Kenrad VT231 Black Glass with a Sylvania VT-231 in my amp. Two very different tubes providing dynamic holographic sound.
And a Tung Sol BGRP in my preamp. 

What’s a BGRP?

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.

It is very often the case that when dual triodes, like nearly all the tubes so far mentioned in this thread, are used in circuit, only one of the two separate triode sections is actually used.  But what is a BGRP? Thanks.