Charles1dad 6-28-2017 It is my understanding that the VAC Phi series of amplifiers are class AB and not pure class A circuits.
I’m pretty certain that this comment by Charles is correct. One indication of that can be inferred from the ratings of the mains fuses that are used, which can be seen in rear panel photos that are available on the web. For 120 volt operation the Phi 200 (for which the two channels are rated to provide a combined total of 200 watts) uses a 5 amp fuse, and the Phi 300.1 (for which the two channels are rated to provide a combined total of 300 watts) uses an 8 amp fuse. Assuming something like a 2:1 margin between the current rating of the fuse and the actual amount of current it would be conducting, that would mean a maximum AC consumption of about (120 x 5/2) = 300 watts for the Phi 200, and (120 x 8/2) = 480 watts for the Phi 300.1. Those consumptions are **much** too low to be consistent with pure class A operation for the specified output power ratings. A pure class A 200 watt tube amplifier would probably consume somewhere between about 800 and 1000 watts continuously, while a pure class A 300 watt tube amplifier would probably consume somewhere between about 1200 and 1500 watts continuously. Those kinds of AC power consumptions would blow the specified fuses almost immediately.
Regards,
--Al