Having a blast with my recently completed TC-15! Just to pass along some info and favorite mods:
1) Having really good luck with a Winged-C brand EF-86 tube (tried another by EH and it was problematic).
2) Love the compression on EF-86 channel with the suggested mod of R33 to 220K and R34 to 1M. With the original grid resistors, the EF-86 channel sounded very much like the 12AX7 channel. Now with new grid resistors, it's got a great, sustaining compression that reminds me of the Vince Gill and Brad Paisley Tele sound.
3) Decided to change up the tone controls a bit. I put a Matchless Spitfire-style tone on the EF-86 channel... 1-meg pot with .01 cap to ground... then I modified the contour switch to 3 positions and put it in the 12AX7 channel as a mid control. Using a pot in place of the R10 10K pot, I found that I liked the mid-boost at 10K, 15K and 20K. Put those values on the contour switch... and now I can switch-in the standard 10K mid value, or "hotter and hottest" mids with the 3-positions. I located the switch in the channel's low gain input hole - I never used it anyway.
I have an original 67 Fender Princeton Reverb, an R.I. Fender Bassman with a point-to-point board and a kit-built 18 watt TMB... but now the TC-15 is my favorite of the bunch. Thanks for a great kit, Trinity!