I recently re-capped my RD50 (Rev-B) I replaced all of the electrolytic capacitors. I upgraded C33&34 to 100uf, c35 to 20uf. I then did the BobW mods. The only other mods I have done are to bring the rest of the board to Rev E spec. That included diverting C23 to pin 2 on IC_2 from Pin 1 and changing R1, R21 and R22 to the Rev E values.
The result is that I now have a much nicer sounding amp with far less low end hum, it has a much nicer distortion on the limiter channel - previously it was very dark and muddy. The two channels are much more evenly matched in tone.
I do have a problem, however, at higher volumes or gain on the limiter channel. Above 3 or 4 on the master volume I start to hear a blooming in the low end on lower notes and then above 5 or 6 the output valves appear to be self-oscillating - I can see a blue ring appear when this happens. I have tried different valves, limiter and output, that I have spare and not much difference apart from the fact that with some different ECC83s the oscillation will start earlier or later on the volume dial which I guess is down to different amounts of gain in the valves.
I am a tube-modding newbie so please be gentle. I am amazed at the difference I have made in tone but would like to sort out the problems at the louder settings so any help would be much appreciated.