I did some experimentations in my 5.5 and came up with similar results as DGAD saw between the Svetlanas and telefunkins when i used NOS Mullard 12ax7 and the Svetlanas. The mullards gave up the details in the sence of room space and in the top end, especially cymbols, that the Svetlanas couldn't touch. The Svetlanas on the other hand gave the system more energy...toe tapping groove if you will, and more bass.
The Mullards also seem to have less gain or maybe it's just that the sound is smooothed out reletive to the svetlanas, maybe both, because i find myself turning the preamp up significantly lounder with the Mullards before i percieve things to be loud. Trying to talk to my wife with the system going suggested that the mullards may get louder than they seem.
I'd like to try the groove tube reissue mullard AX7 to see how they do relative to the NOS. $30 or $40 each for a balanced tube would be a lot better than the $100 ea for the NOS and they probably wont't go away.
the whole 12a family is pretty interchangeable techically speaking. see the referenced site if you want more info. Also look at the Phase inverter discussion to see the variation found in tubes. In the end tube rolling can be as crazy as chasing the perfect cable.
http://www.guitaramplifierblueprinting.com/Tubeprimerandselection330.pdf
http://www.guitaramplifierblueprinting.com/files/Phaseinverter.pdf
After you get all this info in your head it all boils down to what sounds good.
I was trying a 12at7 i stole from my 5.5 as a phase inverter in my guitar amp in place of an ax7 to drop the gain and increase the current some to improve dynamics. my amp hated the added current from the at and buzzed like hell. I'm planning on trying some NOS GE 5157 which have a similar gain but different current. I also swapped a couple of svetlana ax7s, that i also stole from my 5.5, a GE12ax7 and a couple of sovtec ax7wts i had in the various preamp positions of my guitar amp. Each swap changed the nature of the amp pretty dramatically.
The Mullards also seem to have less gain or maybe it's just that the sound is smooothed out reletive to the svetlanas, maybe both, because i find myself turning the preamp up significantly lounder with the Mullards before i percieve things to be loud. Trying to talk to my wife with the system going suggested that the mullards may get louder than they seem.
I'd like to try the groove tube reissue mullard AX7 to see how they do relative to the NOS. $30 or $40 each for a balanced tube would be a lot better than the $100 ea for the NOS and they probably wont't go away.
the whole 12a family is pretty interchangeable techically speaking. see the referenced site if you want more info. Also look at the Phase inverter discussion to see the variation found in tubes. In the end tube rolling can be as crazy as chasing the perfect cable.
http://www.guitaramplifierblueprinting.com/Tubeprimerandselection330.pdf
http://www.guitaramplifierblueprinting.com/files/Phaseinverter.pdf
After you get all this info in your head it all boils down to what sounds good.
I was trying a 12at7 i stole from my 5.5 as a phase inverter in my guitar amp in place of an ax7 to drop the gain and increase the current some to improve dynamics. my amp hated the added current from the at and buzzed like hell. I'm planning on trying some NOS GE 5157 which have a similar gain but different current. I also swapped a couple of svetlana ax7s, that i also stole from my 5.5, a GE12ax7 and a couple of sovtec ax7wts i had in the various preamp positions of my guitar amp. Each swap changed the nature of the amp pretty dramatically.