R13 is shown on the layout as 3M3 but on the schematic as 47M. Is this a typo or is any large value ok here? I can't find a 3M3 so was planning to substitute 4M7.
Also, what voltage is likely to be across the paralleled C15 10 pF?
I don't think a 4.7M is a good idea. You have to remember that Fender really tweaked the values of the parts in these amps. In the case of the 3.3M resistor, you have to remember that this is the non-reverb guitar signal path to the PI. Yep, it passes through the 3.3M resistor and that 10pf cap is a treble bypass cap. If you want to ruin the sound of a Fender reverb equipped combo amp try a 50pf cap across the 3.3M. Virtually every part of the circuit has already been tweaked by the original designers, keep this in mind.
I don't think a 4.7M is a good idea. You have to remember that Fender really tweaked the values of the parts in these amps. In the case of the 3.3M resistor, you have to remember that this is the non-reverb guitar signal path to the PI. Yep, it passes through the 3.3M resistor and that 10pf cap is a treble bypass cap. If you want to ruin the sound of a Fender reverb equipped combo amp try a 50pf cap across the 3.3M. Virtually every part of the circuit has already been tweaked by the original designers, keep this in mind.
My best advice: Find a 3.3M resistor.
yes, that would be the same! for the 10pF you can use anything rated above 400-630V