Pulling 2 tubes loses 3 dB, not enough to really hear. It warms it up a bit perhaps. Using 6V6s or EL84s (with Yellowjackets) will drop it to 30-40w, which is about 6 dB and will be audible but not earth shatteringly different. Part of the problem is that the robust power supply still gives you a hard attack on notes, unlike the power supply of most 30-40w amps. Still more reduction would require an attenuator (another 6-12 dB will be quite audible and won't tax the amp) or modding the amp for cathode bias or triode mode switches. With cathode bias, triode mode, 6V6s you'd be pushing about 15-18w (or pulling two tubes and triode mode, 6V6s). Remember, if you pull tubes, you have to set the output impedance to twice the cabinet value (16 ohms setting for an 8 ohm cabinet).
