[darkmonohue]

I just got a 601A, and I'm enjoying it enormously.  I've heard that the sound of the 601A can be improved by swapping in a 12AU7 for the 12AX7 that comes stock. Has anyone tried this? With what results?  Any particular brands of 12AU7 that work well?  Thanks.

DM

[Bill Baker]

Greetings,
   Due to the different parameters of these two tubes, I do not recommend installing the 12AU7 in place of the AX7. I have done this in Jolida's Hybrid designs and even in the tube amps but don't recommend it. The 12AU7 would produce more distortion in these circuits as they are not designed for optimal use with the AU7.

[darkmonohue]

Thanks for the heads-up.  Is there a 12AX7 you particularly recommend?  I'm using a cryo'd JAN right now, which seems to me a big upgrade from stock.  

Greetings,
   Due to the different parameters of these two tubes, I do not recommend installing the 12AU7 in place of the AX7. I have done this in Jolida's Hybrid designs and even in the tube amps but don't recommend it. The 12AU7 would produce more distortion in these circuits as they are not designed for optimal use with the AU7.