Replace 12AU7 with 6SN7 ?

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

Ghostrider, just saw your post. Great minds think alike!

Regards,
-- Al

"I am not going out of my way to be rude, I would just think that the manufacturer's word would trump anyone else's. "

Al's an exception.

Simply replacing 12AU7s by 6SN7s would double the filament current drawn (3.6 amps vs 1.8 amps for 6 tubes). That could easily burn out the power transformer if its rating is marginal.

The above statement is correct. Unless you can measure this yourself, and are capable of modifying your amp yourself, then don't try to swap out the tubes. Overall the amp would operate but you don't know how the current will effect the other parts in the amp. Most tubes will operate in a range and obviously if it all matches, the better the unit should sound. Therefore, the manufacturer should know what is best for their design.

Happy Listening.