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help with 6SC7 to 12AX7 adapter


2019-04-11 3:18 pm
I recently came into a Groove Tube adapter that is suppose to allow you to use a 12AX7 in a 6SC7 socket. Thought I would try this in one of my GE and Fisher tube phono preamps that use 6SC7. Long story short, with the adapter it passes signal, but has a pop a regular intervals. Is there anything unique about these 6SC7 phono pres that would require re-wiring the socket even with the adapter?
Have you tried more than 1 12AX7 specimen?

There's not much to the adapter's internal wiring: "strap" the heaters for 6.3 VAC and tie the 2 cathodes together.

FWIW, a 5751 is electrically closer to a 6SC7 than a 12AX7. Grid and plate connections are simple pass through.

Those GE style preamps rely on the inductance of GE variable reluctance cartridges to get the RIAA curve correct. Tweaks, including a 47 Kohm I/P impedance, are needed to use a modern MM level cartridge with a GE style phono preamp.


  • Fisher PR-6 Mono Phono Preamp.gif
    Fisher PR-6 Mono Phono Preamp.gif
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I think Groove Tubes did 2 versions of the ''SUB'' to 12AX7. One for 6SL7 (SUB-1) and another for the 6SC7 (SUB-2) I'm guessing? Which one do you have? If you have a multimeter it should be easy to work out which pin is connected to which on your SUB...
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2019-04-11 3:18 pm
6SC7 to 12AX7 adapter

Have an adapter made by Groove Tube, the Substi Tube #2 made to adapt from a 6SC7 to a 12AX7......The necessary rewire is taken case of inside the adapter base FOR A NORMAL 6SC7 circuit...........the adapter however does not work in my application, a GE Phono Preamp.. .....My question is, do I need to change wiring on the 6SC7 socket to get the adapter to work?? Anyone familiar with these?? thanks jack