Originally Posted by phase_accurate
I tend to the same answers as tinitus:
Did you make a coarse check of frequency response ? Maybe some coupling C is too small or something else is giving you a insufficient low-end response.
As already mentioned the frequency response of guitar pickups is very load dependant. Electrically (i.e. without looking at things like PU position, pole size, single-coil or humbucker etc) they usually form a second order lowpass with a peak before the final drop. Your amp might be unluckily loading the PU(s) in such a way that you end up with the peak in an unpleasant frequency range.
Thanks for the response, yeah checked cap sizes coupling and cathode decoupling, and the bootstrap cap is ok (thanks to the other thread). The load on the guitar is a 1M grid leak resistor and then a 47k grid stopper to the grid itself, which is not in the least biased hot, so not leaky.
I covered 3/4 of the back of my cab and it's sounding much better, so i suspect it's cab and speaker issues.