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It Can Be Done...But, Not Easily...

As the two tubes are "different" in their biasing, plate loads/gain and filament pinout, switches and switched in-out parts would be necessary.

The OP, or anyone seriously interested in this implementation, should probably research the differing resistors required for cathode bias and plate loads for a given high voltage power supply. Also, finding noiseless, accommodating switches will not come easily. The gain is very different among these two tubes.

Perhaps, after much research, you might consider different tube types, like a 12AX7 vs. 12AT7 or 12AY7 vs. 12AT7 or 5751. A 12AY7 vs. 6DJ8/6922 might also be easier to implement.

Please also take note of a new breed of hybrid tube preamps and headphone amps, reasonably offered from Hong Kong and China, by companies like Indeed, Bravo, Little Bear, etc. Some of these can be switched easily and quickly to use either 6922 or 12AU7 tubes ! However, this is because their very low plate voltage/hybrid operation creates a unique combination of "gain with a very low output impedance." Thus, while a stereo headphone amp can be accomplished with one 6DJ8 or 12AU7 plus two FETs mounted on heatsinks, that same 32 Ohm to 600 Ohm output capable headphone amp can also be used as a very competent line stage preamp. Sound quality is surprisingly very good, but remember those tubes are now hybrid devices. So, it can be done...


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  • It Can Be Done...But, Not Easily... - Interstage Tranny 19:34:04 12/16/16 (0)

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