Preamp / tubes question

[bsee]

Okay, so I will shortly have an F2-B. My intent is to cascade the channels looking for a more tube-power-amp tone than I was getting from the pure F-1X. This, I believe, will be similar to the way my Fender TBP-1 is *supposed* to work.  
 
My experience with the TBP-1 has been that the second gain stage breaks up too much and not in a musical fashion. I fear that possibility, or at least that it will be very touchy, on the F2-B, and so we get to the questions...
 
Might it be appropriate to put some kind of lower gain tube in the second stage? Would something like that improve the preamp's ability to generate a warm tone without completely breaking up? Do I need to reduce my on-board preamp gains to give the tube preamp gains more room to work? Any recommendations for specific tubes, or issues with running lower gain tubes in such a preamp circuit? I was thinking about a 12AT7 or 5751, is there much gain difference between them, or are they close enough that it will just be a matter of taste?
 
I realize that the F2-B wasn't designed for it, but is it possible to modify one to make cascading easier and/or to make it so that the second stage could be in/out based upon a footswitch? I suppose this could be done with some sort of A/B switch outside the box, so I'll have to consider that, but the further away it is from the amp, the more wire the signal is going to have to go through.  
 
-bob

[pace]

Bob, don't over-think this!!!!
 
I cascade the channels on my F2-B, and every setting I've settled on sounds musical and warm. An AT7 or AU7 might give you a different gain structure, but there's enough wiggle room in the F2-B's circuit that you probably won't need to swap out a channel.  
 
If you use the M(mono) out of the preamp, you'll only need to control switching from the front end. A Morley A/B/both switch along with a bypass switch in the cascade would give you every possible option.  
 
For guitar, I've been running my F2-B in stereo out to a Superfilter w/ channel A in high-pass mode to help focus the bottom end, and channel B in band-pass mode to narrow out the content of the gritty channel.

[sonicus]

I have recently obtained several sets of Telefunken 12AX7 tubes .
They were produced in the smooth plate and ribbed  plate variety in different runs of production .  I have both kinds and have been swapping them back and forth in my F-2B.   Smooth plates win !

[edwin]

While it's very possible to get excellent tones from cascading channels, it's not the same as power amp distortion. Power amp sections not only have tubes like the preamp sections, but also have output transformers. Because of the different way the tubes are used in a power amp section, they saturate differently and when you add that to output transformer saturation, you have some pretty different. There are some rigs, like the SWR Interstellar Overdrive, that do set this up as a preamp (or very low power practice amp) and it works quite well.
 
That said, if it sounds good, it is good!