Could be that the amp is biased a little hot. You might want to check the bias setting of the EL-34 output tubes. David Manley, the fellow that started VTL in 1989, suggests in his book that 27mA is the ideal setting for EL-34s and I have found that this setting gives that tube a nice rich sound. Measure the mV from pin 8 of each EL-34 to ground and divide that number by the value of the cathode resistor (Ohm's law I=V/R) to come up with the bias setting.
signs your pramp and power tubes need replacement
Having a little early fatigue from listening to newly aquired tube amp.