Balanced Triodes

Just wondering if anybody has experimented with using driver tubes with balanced triodes for the phase inverter sections? Just wondering what the effect on sound quality would be? Seems obvious that you would also want to use a tube with well balanced triodes in the main driver position, too. Maybe the result is not noticeable so having the triode sections matched is not really worth the expense. Luckily, I will be getting a few tubes with matched triode sections this week to use in the main voltage amp stage, but am thinking I should have also ordered a pair of matched tubes for the phase splitters too.

Thanks

Phil

polarflux wrote:Just wondering if anybody has experimented with using driver tubes with balanced triodes for the phase inverter sections?  Just wondering what the effect on sound quality would be?  Seems obvious that you would also want to use a tube with well balanced triodes in the main driver position, too. Maybe the result is not noticeable so having the triode sections matched is not really worth the expense.   Luckily, I will be getting a few tubes with matched triode sections this week to use in the main voltage amp stage, but am thinking I should have also ordered a pair of matched tubes for the phase splitters too.

Thanks

Phil

Unbalanced triodes does not sound good in a long-tail phasesplitter. Been there, done that.

I can see it being a lot more noticable on a high gain tube like the 12AX7, or maybe even a 12AT7, but is that really a problem with a 12AU7?

I find that swapping center tubes does affect the balance, which makes sense as that's the first stage amplifier for both channels - I've got one with closely matched triodes that seems to center out nicely all on it's own without having to tweak the balance.

Yet another reason I originally went with dual volume controls, and glad I did. It doesn't usually take much of a tweak to center the system - just a nudge takes you from    to    ...

Actually with the center tube each section has it's own cathode resistor to set the bios current. Unless one section is very weak or has other problems the resistors should make them about equal. With the long tail however you only have one cathode resistor for both sections so matching is far more important. Adding a Constant Current Sink to the cathode as I think Roy has done in his latest driver boards help make the 2 sides equal but a balanced tube would make it even better.

Yes, you need balanced triodes