Originally Posted by gibosi
Would you and/or Ctritical Bill post a link to one of these breadboard sockets that allow one to add resisters? The 6DJ8 family, including the 6922 and 7308, could well be my end-game tubes. And while these tubes sound incredibly good now, it does make sense that if we can optimize the electrical values, or at least get closer to optimum, these tubes may actually sound better. Thanks! :)
It would be great if we could determine "optimized" values for all the resistors used for different tube types, whether noval or octal. But, looking at the 6DJ8 datasheets again - and listening to those tubes on my MK IV - I keep thinking that it's almost like the amp was made to use those tubes...
The cathode resistor values should definitely be pretty close to recommended specs for 6DJ8 types. At least moreso than for any of the 12Ax7 types. From memory, I think the values also fit a 6SN7 pretty well too, though they didn't seem totally out of spec for 6SL7 tubes.
Again, 6922/E88CC & 7308/E188CC types may actually be some of the best "fits" we can find for our LD amps, just because of their tolerance for higher plate voltages. The 6922 has both the best sound quality I've ever gotten out of the amp, and also the best "running conditions" I've ever managed to get, with low, low temperatures and low current draw.
Getting real world values for those tubes really would be great, if only just to know whether or not it's worth to actually invest in the best tubes, and potentially just "mod" the amp itself to use those tubes.
By "mod", I'm thinking more of socket modding: either cutting the PCB trace connecting pins 5 and 6 so two separate tubes can be used on each socket with a very basic adapter (or no adapter at all if pins were to be cut and the good old straps were to be used), or either completely replacing both B7G sockets with two B9A sockets with only 5 pins connected for each; or even alternatively, using a single B9A or octal socket, integrated in a new drilled central hole between the original driver tube sockets and soldered in all the right places on the PCB - without any of this being visible outside the amp. Best of both world, you'd still have the two original B7G sockets to do whatever you want, and also a single noval or octal socket to use a single double triode if you choose too.
Anyway, confirming the electrical validity of what we've been doing - despite the LD amps' apparent flexibility - would be a good idea.
Sorry for the rant again, I just have too many ideas late at night, and not enough outputs to actually use them or clear them lol... Just food for thoughts for all the hardcore modders on this thread. Hell, I actually seriously considering permanently modding my amp you know; just so I could use my fav' tubes without any adapter at all.
Seriously though, I'm just waiting for someone to try and add a third "central" B9A socket on their MK III or IV, or to try and replace the driver tube sockets with two B9A sockets... I know someone will eventually try and dremel a third hole in there lol...
Edit: Look on the bright side, some people just don't have limits to their tube budget... I'd been following an ebay auction for about a week, knowing very well how it would turn out, but I didn't think anyone would be crazy enough to fork out $627 for a pair of essentially un-guaranteed E88CC. Yes, Philips Heerlen; yes 1957; yes D-getter; yes pinched waist; but still... $627? For driver tubes?? Color me appalled...
I do hope these turn out to be "god tier" tubes for the guy who bought them... Lol.
Edited by Audiofanboy - 12/1/13 at 4:42pm