That is why I have my Ceriatone built Express to make changes to for experimenting besides the Express amps I built and it has been fun to have that additional amp to experiment with. The changes have allowed much more bass response to my ears by a simple swap of caps.
I never did look to see if I have two primary taps on my PT I will have to take it back out of the head cabinet once again to see, might go with 6k6 too.
I may be incorrect, and sorry if I am, but I recall reading that Ken used a 4x12 with heavy magnet greenback celestions (I think they're the 30w versions) in it when tweaking express amps.
If that is true it would really change the way that he would have tweaked the circuit. I have a 4x12 with those speakers in it (a great deal that I lucked into) and it has A LOT more bass output than most other cabs that I've had. I've yet to try it with an express style amp, but it may be a part of the puzzle.....
I think I will try a resonance control once i get the master volume installed. still anticipating a decrease in high end with one installed.
-The amp has been used so far in the practice space which is a big empty room and live on stages with pro pa gear. sits perfect just could use a nudge more low end...or at least more control over the resonance of the low end.
-I had a bad cat head case sitting around. Gonna retolex and redo the plate.
-i use a 4x12 orange cab with h30's and celestion 75's in a x pattern, though i have tried an original greenback cab and prefer the setup i have now.
-i also use it in conjunction with a vox ac30 and it is just killin it right now!!!!
-there will be some studio recording done soon with my setup, I'll send a link as soon as done