What tubes are being used with Sonic Frontiers L1

Your best bet is to put the better tubes in the back as they affect 85% of the sound by accounts that I've heard. I have 4 NOS Russian mil-spec tubes in the front four and a pair of early 70's Siemens E88CC's in the rear. Granted my CDP (Musical Fidelity A3CD) doesn't have a great deal of slam to begin with it is my opinion that if you are looking for slam that you should look beyond these tubes as well. Having said that, these tubes do sound much better than the stock ones. Good luck.

Cosmic is correct regarding the rear most tubes affecting the sound most of all. I have used Siemens, Telefunkens, RCAs, Amprex and Sovteks. Each had their own characteristics and they are all subjective. I personally really liked the Siemens, RCAs and Telefunkens.

A local Line1 guru who spent a year trying every NOS tube out there saved me the effort, I went with his recommendations, though have tweaked the sound depending on which tubes are in which locations. Tungsrams give an almost-startling amount of image dimensionality and sizing, a smoother treble while still retaining the solid-state bass slam of the Line1. Electro-Harmonix are a slightly faster cleaner sounding Sovtek. I use the Tungsrams in the back (V1) and front (V3), with the EH in the center (V2) locations. Depending on your tastes, running the EH in both V2 and V3 may sound better, and be cheaper too (EH are in production at about $12, tungsrams can be $40+ ea). My understanding with Bugle Boys would be to use them in either the front or rear only in combination with 4 EH. I haven't yet heard this combo, or for that matter any of the 100 other combos that others can offer up. But I am quite happy with the sound of the setup I described...

I recently tried Siemens CCa (late 60's) and Telefunken E188CC in V1. The CCa is already very good but after using the E188CC in V1, the sound changed so greatly as if I had changed a new audio system. The power of the Telefunken E188CC is so great that I immediately ordered one more pair. I am using Amperex 6DJ8 orange globe logo in V2 & V3. Will change them to 6922 version later as 6DJ8 has shorter life.