Yogi and Mofi, yes, the 12 and the 6 are the filament voltages that the tubes are designed to be operated with. Obviously, applying 12 volts to a 6 volt filament would result in pyrotechnics.
Looking at a tube manual I have, though, I see that the 12AU7 apparently has a center-tapped filament, and its filament has two ratings, 12.6 volts at 0.15 amps, or 6.3 volts at 0.3 amps. The 6SN7 rating is 6.3 volts at 0.6 amps.
I would surmise, therefore, that SOME designs operate the 12AU7 by applying 6.3 volts between the center tap of the filament and both of its end points, thereby operating the two halves of the filament in parallel.
Other specs on the two tubes are generally in the same approximate ballpark, except that the 6SN7 can handle higher power levels, especially in its GTA and GTB variants, which are also rated to be able to handle considerably higher voltage levels.
So IF the adapter steps down 12 volts to 6 volts, OR IF the component is designed to operate the 12AU7 at 6.3 volts (with the two halves of the filament in parallel), AND IF the power transformer can comfortably supply the doubled filament current that would be required by the SIX tubes, it may be within reason to make this substitution. However, unless one is familiar with the details of the design of both the specific component and the adapter, and unless one knows exactly what one is doing, disaster is being invited.
Regards,
-- Al
Looking at a tube manual I have, though, I see that the 12AU7 apparently has a center-tapped filament, and its filament has two ratings, 12.6 volts at 0.15 amps, or 6.3 volts at 0.3 amps. The 6SN7 rating is 6.3 volts at 0.6 amps.
I would surmise, therefore, that SOME designs operate the 12AU7 by applying 6.3 volts between the center tap of the filament and both of its end points, thereby operating the two halves of the filament in parallel.
Other specs on the two tubes are generally in the same approximate ballpark, except that the 6SN7 can handle higher power levels, especially in its GTA and GTB variants, which are also rated to be able to handle considerably higher voltage levels.
So IF the adapter steps down 12 volts to 6 volts, OR IF the component is designed to operate the 12AU7 at 6.3 volts (with the two halves of the filament in parallel), AND IF the power transformer can comfortably supply the doubled filament current that would be required by the SIX tubes, it may be within reason to make this substitution. However, unless one is familiar with the details of the design of both the specific component and the adapter, and unless one knows exactly what one is doing, disaster is being invited.
Regards,
-- Al