Well folks, I think I may just have found my endgame tube(s) at long last, and I'm afraid it's ciao to the 6DJ8s - never thought that would happen! Even my beloved Tesla E88ccs (gold pins and grids) have been blown out of the water...by the Siemens C3gs I have finally managed to complete the adapters for - they are an 8-pin pentode (can be triode connected) with different pin-out, of course, to the 6AK5.
Apparently they were conceived by some VERY demanding engineers, wanting uber low distortion, microphonics, noise etc etc but with high gain, linearity and very long life. All I can say is they worked miracles, because they have not only filled the slight gaps in the otherwise excellent Teslas, but also surpass them in ALL areas - given my equipment and ears, of course.
Bass is phenomenal, in detail and extension (slam is too crude a word to apply to these beauties).
Treble ditto, without the occasional sibilance of the Teslas.
Mids have returned nicely, with no loss in the other frequencies - in fact no range dominates to the detriment of others.
Soundstage is truly remarkable - a magic trick that manages to achieve the 3-dimensionality of the Teslas with even more detail...a rare ability I would suspect.
Imaging is precise, along with instrument and voice positioning/separation. Vocals are slightly more forward than the T's, giving a slightly more intimate musical experience while retaining a fine overall balance.
The tonal range is immense, along with dynamic range - from attack thru decay, instruments are taking on a whole new (magical) persona.
And the low noise/high linearity pre-requisites are manifested by the dead silence in a 'black' background, and a deliciously 'clean' sound of wonderful clarity.
In other words, I am totally blown away, in case you hadn't guessed!
Perhaps my (obsessive) desire to keep to a minimum the number of in-line connections and mix of metals may have also helped somewhat...in line with my previous mods, I decided to use pure silver wire for fitting tube to LD socket - in fact I bit the bullet and did away with an adapter as such and connected (scarily!) 1mm wire direct to the tube pins, said wire also acting as the B7 pins, instead of a cut-away tube base. Sealing things in resin to (hopefully) prevent connections becoming DISconnected meant I only really had one chance to get things right...a bit of a nightmare, to say the least!
Anyway, thankfully all was well (so far) and the final result has proved to be worth every ounce of sweat and nervous exhaustion.
This 'pentode' certainly seems like no other, and would explain Yamamoto's choice of the C3 family for some of his lovely amps...
The above, of course, is NOT the right photo - (don't know how to remove it!). Hopefully second time lucky...
That's more like it!!