I'll probably just muddy the water but here goes:
IMO, thinking in terms of "the grid and cathode are in-phase with each other and out-of-phase with the plate" can make your head spin regarding LTPIs. For me, the key was taking the following as truth regarding triodes (and it is the truth):
A signal input at the grid is amplified out-of-phase at the plate.
A signal input at the cathode is amplified in-phase at the plate.
In a LTPI, there is no cathode bypass cap so there is signal on the cathode and both cathodes are tied together. So the input for the second (bottom) triode is at the cathode...therefore the amplified signal at the second plate is in-phase with it (which is the opposite phase of the first plate).
Amps with no NFB usually just have the tail directly grounded...that 47ohm ground resistor in a BF Fender is just part of the NFB voltage divider (820 and 47 ohm). No 47ohm resistor and there would be no NFB since it would then be directly grounded. If you'll notice, BF Fenders that take an 8ohm speaker have a 47ohm ground resistor and ones that take a 4ohm speaker have a 100ohm...because there is more NFB voltage coming from the 8ohm tap.
Hope that helped...but I have a feeling I completely missed the point.
IMO, thinking in terms of "the grid and cathode are in-phase with each other and out-of-phase with the plate" can make your head spin regarding LTPIs. For me, the key was taking the following as truth regarding triodes (and it is the truth):
A signal input at the grid is amplified out-of-phase at the plate.
A signal input at the cathode is amplified in-phase at the plate.
In a LTPI, there is no cathode bypass cap so there is signal on the cathode and both cathodes are tied together. So the input for the second (bottom) triode is at the cathode...therefore the amplified signal at the second plate is in-phase with it (which is the opposite phase of the first plate).
Amps with no NFB usually just have the tail directly grounded...that 47ohm ground resistor in a BF Fender is just part of the NFB voltage divider (820 and 47 ohm). No 47ohm resistor and there would be no NFB since it would then be directly grounded. If you'll notice, BF Fenders that take an 8ohm speaker have a 47ohm ground resistor and ones that take a 4ohm speaker have a 100ohm...because there is more NFB voltage coming from the 8ohm tap.
Hope that helped...but I have a feeling I completely missed the point.
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