Re: 50w 5150 iii clean channel.
To the OP: Don't you have a mini Jubilee? That amp will do an astonishing clean with kT66 tubes. It doesn't kill the drive channel either. The overdrive is just a little different in a plexi kind of way. Throw a reverb in the loop and you will have an impressive clean tone. And you will forget that there is shared input gain and EQ between the two channels.
The downside is that you can't put the amp back in the head shell without notching the mounting frame for the back grill with most KT66s. And you will need to remove the bear trap tube retainers with kT66s. Alternatives to the KT66 such as the KT77, 6L6/5881, or 6550 might give you that without needing any modifications though. The amp responds nice with 6CA7s too, with deeper, tighter bass, but the cleans on the 6CA7 may be too dark for channel switching. The mini Jubilee is cathode biased and can safely take any those above tubes with out adjusting the bias. Just swap em out.
