I have this amp, which has new caps, tubes, 3-prong power cable, etc. It is really bright and sound great for clean tones, but it sounds sort of dull whenever running any kind of drive pedal through it, almost like you're hearing it through dynamic mic or speaker simulator. I just recently replaced the speaker with a Green Beret, as I am a fan of the "british" sound, and it was a big improvement to the sound overall. I have 4 different drive pedals and I can get them all to sound good through it now... but it still lacks bite in the high end. Do you think I should have tried a different replacement speaker, or is it likely to be a matter of the amp's design? Maybe there's a mod I could do to the circuit, or maybe I need a new transformer? The schematic is so simple that I don't see anything obvious that would be acting like a low-pass filter or anything.
Here's the schematic for reference:
http://www.0rigami.com/gg/ga5_crest.pdf