Tarheel, have faith my friend. I too have the HP and be live me rolling those two middle tubes V11 and V12 make a very noticeable difference. I use all NOS tubes. 1960s Mullard El34 power tubes 1950s RCA black plates to run the grids of the power tubes V9 V10 V13 V14 and I have a few sets for V11 and V12 1950s Mullard 12AU7 long plates, 1950sTelefunken ECC82 smooth plates, 1950s CBS/Hytron 5814A, 1950s RCA 12AU7 black plates, these all bring a little something different to the table. Andy at Vintage Tube Services and Brent at Brent Jesse Recording have been very helpful in guiding me and supplying my tubes. Very satisfied.
Have fun with
John