I restored the original AC15 values for the filtering capacitors, as well as the coupling capacitors. As I performed the replacements at the same time, it is difficult to say which contributed most but I can confirm that the amplifier feels more dynamic and the sound is fuller and smoother, without compromising brightness if that's what you are going for. The replacement values I used are the following:
Signal Caps:
- C13: 220pF
- C22: 100pF
- C21: 500pF
- C23: 47pF
- C24, C25: 22nF
- C7, C10: 100nF
- C12, C14, C27: 47nF
Filter Caps:
- C1, C2, C19: 16uF
- C5, C6: 8uF
- C3, C4: 100nF (note: those are not electrolytics)
At the same time, I decided to implement the following mods:
- I replaced the Normal channel's volume pot with a Push-Pull pot and put R17 on its switch. R17 is the limiting resistor that is permanently reducing Normal channel's gain.
- I replaced the Top Boost channel's volume pot with a Push-Pull pot and put the bright cap (C22) on its switch. Since the Bright cap is so small in value, the difference is very subtle but still it's a nice option to have.
- I replaced the A200K Master Volume pot with A500K. This solves the problem of reduction of volume even when the Master Volume is fully clockwise compared to the non-master. The downside is that the Master Volume taper is a bit steeper (not as gradual) but I do not mind.
Lastly, I replaced the Celestion G12M speaker with a Celestion G12-35XC which complements the amp very nicely (there was nothing wrong with the G12M mind you).
All in all, the improvement is quite drastic and I am really happy with the amp now.
