Let's start with the tubes.when i first purchased my 5's,I used tesla el34's did not care for them,bass was muddy and the tubes are very unreliable,called conrad johnson and they put me in touch with BILL THALEMAN,the electrical designer of these amp's,after the modification's bill recommended the svetlanas el34's,the mids are very warm,the treble to die for extremly liquid and absent of any grain,the bass is very musical a great improvement over the tesla's.cost of mod's will run about $500 a pair,i supplied the pwr cords.
turnaround time can run 3 to 4 week's.my amp's were in a a/b comparisons with the CJ8a's which retail for over $15000
tha 8a's were a little better in the bass department that's about it.