Is the power tube cathode bypass cap still 25uF? If you wanna add some heft, try bumping that cap to 100uF! I tried this on my Allen Classic 10 and if got rid of some of the boxiness these amps are famous for, gave it an 'Oomph' I always though it lacked. It's subtle, but appreciable. A word of warning though, in my amp I cut bass earlier in the circuit first before I did this. The first cathode bypass is 10uF and the first coupling is 10nF. I think it's best to trim bass earlier and let it out at the end. it"s funny but the most bass attenuation in these Tweed circuits is at the power tube cathode bypass cap.