Looks neat Billy,

From what I understand, the 12AX7 will substitute for the 6SQ7. Note that the 12AX7 runs 12 volt heater (2 x 6.3V heaters in series) but they can be placed in parallel and run 6.3V

I think the gain is identical and as it's operating as a pre-amp, I doubt that the rail voltage would need any adjustment.

They are both double-triodes, so I'm guessing that you only use 1/2 of the valve.

The 12AX7 has a slightly smaller package, which might be useful.

HTH
Trev


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