Hmm, some interesting points have been raised here.
While, I agree that it may look like only a handful of people are actively following up on each and every new trend - read tube type - I also believe that at least a few times more people are just lurking around here are still pretty much trying every new things that's brought up here. This is one of the rare threads I'm active on for example; but for two, maybe three threads I often post on, there's a lot more I always follow and never make myself know in - a.k.a. lurking.
Anyway, price-wise, many of these premium, no - or barely any - compromise double triodes, especially the 6922/E88CC & 7308/E188CC, can be found without even looking that hard - basically camping 10 ebay listings for a week - and for very decent prices. Granted, not $8*2=$16, but you can easily get single European Philips E88CC or E188CC for $30-50, or a single Bugle Boy or whatnot - less premium - for $20-30.
So, yeah, compared to where the thread started off from - people paying $35 for a pair of "matched" Voskhods from Yen Audio (scandalous in its own right) - I think we've definitely moved in the right direction. At least in terms of sound quality, even though price-wise we haven't ramped up that much all in all - if anything the heptode period was closer to being the exception in terms of price paid per tube!
This being said, we've also come to a point where I highly doubt many new and improved whole tube families will pop up out of nowhere, so we can finally dissociate the "game" of tube rolling from the "end" of tube rolling, which is supposed to be getting the best sound out of one's amp. Nothing forbids people from going back to previous tube types and testing new ideas on them just for the heck of it; or finding more oddball tube types for fun, even knowing that it probably won't be to get them the best sound ever.
Even I have a few ideas I never managed, or had time to, put together before "we, the people"; wait no... That's not right... "We, the handful" leaped in the double triode abyss. Here's a few ideas I had a few months ago, cheap and interesting ideas :
- Using a good ol' pentode - the examples I'd read about used a 6AU6 type - with the screen grid (g2) as the anode, and the actual anode grounded. I know this should work in theory, since it's used in some applications. People over on the LaFigaro 339 thread have used and loved this exact technique in their amp in the driver position, where a I-forget-which-pentode-type is triode strapped in this way. I never got a chance to try this on a LD before, since it used to be difficult to "invert" pins at the socket level, and since there was no place I knew of to easily tie a pin to the ground. Now, with the Vectors, virtually anything is possible, and we've confirmed that the front right screw is an easy path to the ground, so one could just link a wire between the anode pins to this screw and ground the anodes. Then, the screen grids could be rewired with the Vectors to their respective anode pins at the socket level. Just an idea... Should work so long as there's no more than 0.5W of dissipation on the screen grid; and even if there is, it'd still be interesting to try.
- The 6GK5 tube: VHF single triode, frame grid construction - like all the cool kids, and the 6DJ8, you know. This is the point where I'd stopped at just before using double triodes, so I never got a chance to try this tube type. It would need some degree of pins rewiring, but nothing out of this world if one tries hard enough. It's cheap, has pretty good characteristics, a frame grid, and is very linear. I have no idea how it is supposed to be biased since I don't recall we'd been talking about such things back a few months ago... Anyway, just an - cheap - idea.
And on a totally separate note, two other recent ideas, or more like questions actually, that occurred to me yesterday when taking measurements of my amp.
An easy one first, now that we know for sure that that front right screw leads to ground, couldn't we tie the pin 9 shield of 6DJ8 tubes to this screw instead of tying it to the right triode cathode?
A more difficult question now : how hard would it be to make and use a battery-powered supply for the driver heaters (a 6.3V 0.5-1A DC power supply) and could it bring somekind of an improvement to the way the driver tubes function (less hum or noise, better and more stable current supply...)? I can't imagine it would be hard to make, I'm more curious about what it would change. I'm pretty sure I've read examples of people preferring a DC battery power supply to an AC transformer power supply for heating their tubes...
Anyway, I'm sure there are many things we can still work on to improve the sound of our LD amps, without spending $100 a week on new tubes... And that's my point: no one needs to spend that much on tubes if they're tube rolling for fun in the first place!