Advice for gain stage and Master output with tube preamp

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Would moving the 1M resistor to ground (R1) before the 68k change anything? If it's ok I could mount it on the input jack t save space...



Shouldn’t hurt anything and that’s how Marshall and Fenders  are set up
 
This is all basic audio level control. Why so many questions??

This preamp can make output over 40V peak; "must" go there to get "the tone".

You can't possibly need more than 2V-3V for any next stage (except the guts of a Fender).

So you want roughly 20:1 loss.

You mention frequency response from a too-high value pot feeding a line. So don't use the 1Meg pot, that's just wrong. Even when driving just a foot of wire a 1Meg at half-gain will roll-off the top of the audio band.

The 12AX7 stage is taken from a handbook and actually aimed for a 220k load. When you figure a lot of Fenders you see that Leo knew that and often got pretty near.

220k and 10k pot is 20:1 loss and <10K line impedance for all practical purpose.
 
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