tweaking a '59 RI Bassman LTD

[tubeswell]

To cut a long story short, see: http://music-electronics-forum.com/t27114/

I'd really appreciate any comments on the questions I posed in that thread in the above link, mainly:

1) Can I go up to ~250pF for the plate-to-plate shunt capacitance for the LTP Phase inverter without noticeable effect on the audible high guitar frequencies? (presently has 47pF)

2) Can I put 250pF shunt caps from the grid-to-ground on the 6L6s (as Merlin outlines in Chapter 9 (Fig 9.11) in his first book (to 'slug' the dominant NFB pole as he puts it), but have them going from grid to cathode (where the cathode is riding on a 1R bias resistor) so I can mount them on the tube socket pins?

3) is adding and extra 47-100R at the G2 pins for the 6L6s going to help at all with stray RF coupling? (The 470R grid resistors are mounted on the main board in this thing).

(I tried a cut-and-paste to copy the whole spiel here, but it exceeded the character limit)

[sluckey]

1) Can I go up to ~250pF for the plate-to-plate shunt capacitance for the LTP Phase inverter without noticeable effect on the audible high guitar frequencies? (presently has 47pF)

I think you'll hear a difference, but just try it.

2) Can I put 250pF shunt caps from the grid-to-ground on the 6L6s (as Merlin outlines in Chapter 9 (Fig 9.11) in his first book (to 'slug' the dominant NFB pole as he puts it), but have them going from grid to cathode (where the cathode is riding on a 1R bias resistor) so I can mount them on the tube socket pins?

Yes.

3) is adding and extra 47-100R at the G2 pins for the 6L6s going to help at all with stray RF coupling? (The 470R grid resistors are mounted on the main board in this thing).

I don't think so. The strength of stray RF you're likely to encounter would be a factor back in the preamp where the intended signal is weak. But I don't think it's a factor at the PA.