Dr_john:
1) Audio Oracle sold VAC at both Innovative Audio and Sound by Singer in Manhattan for fifteen years and knows what he is talking about.
2) There's a bit more to the issue of getting good bass from a ported speaker like the Sophia when it's driven by a tube amp than just choosing a high powered amp that uses pentodes. Most 300B's do tend to be a bit fat below 30 Hz., yes, but the bass quality you get with a tube amp will be more dependent upon the quality of the output tubes you choose for it, and especially, the quality of the amp's output transformers and size of its power supplies - you can't just think about the damping factor of pentodes vs. 300B's and the choice of speaker cables. You will get better bass if you use a premium 300B like the KR Audio, E.A.T., and to a lesser extent, the better Chinese tubes (Sophia carbon plates or Shuguang Black Bottles). Also with respect to tube quality, it's important to point out that the Renaissance amps feature a push-pull circuit that is demanding on output tubes, running them at 95% of their maximum plate voltage at all times due to the Class A biasing, and for this reason, it's a necessity that carefully selected 300B's be used. I'm not just talking about choosing the right brand of tube (i.e., buying premium brands and staying away from most production coming out of Reflector or Shuguang), but making sure that the actual tubes to be used in the amps test strongly enough to withstand the circuit. In other words, each individual 300B that you put in the amp must first be carefully tested at plate voltages which resemble the voltage 300B's are run at in the Renaissance circuit in order to ensure that they will be able to handle the circuit -- this means that you have to choose a tube vendor who has appropriate testing equipment and who has integrity. Generally, as for transconductance, 300B's for the Renaissance amps should test in the 3,000-5,000 range. In addition, the plate-to-cathode voltage for 300B's in the Renaissance amps is approximately 430 volts dc, with idle current approximately 85 to 90 milliamperes in a self-bias (cathode bias) circuit. Again, this is approximately 5% below the maximum rating for the WeCo spec 300B (PS - only classic "WeCo spec" 300B's can be used in the Renaissance amps, as meshplates cannot handle the voltage, and "super 300B's" like the KR "BLX" have excessive filament current and will fry the amp). Milliamp and transconductance testing for purposes of matching must be done at these voltage levels, and many 300B's, even the best brands, will not make the cut (some KR's, which are very expensive tubes, will not meet these criteria, while a few EH's, which are very cheap, will -- the point is, each individual tube to be used in the amp must be tested in order to determine whether it meets these criteria). Sophia Electric used to market special quartets and octets for the Renaissance amps that met these heightened standards. Once you get a high quality, carefully matched set of 300B's, they last a very long time (8,000+ hours) and are linear into extremely demanding loads (they can drive 1 Ohm loads for short periods). VAC's own 300B's are rebranded Shuguang tubes that are very carefully selected, last a long time, and sound good in the Renaissance amps, but they are not the equal of carefully selected KR's or EAT's.
Regarding the crucial issue of output transformers, the output transformers are better on the Renaissance amps than the Phi amps - they are very expensive, which is the biggest reason these amps cost $14,000 twelve years ago. Before you buy a Phi amp, you should probably talk to Kevin Carter of K&K Audio - he designed the VAC Renaissance amps and can talk to you about the extreme parts quality that they featured. Years ago, when Sound by Singer started to carry Pipedreams, they were trying to find a tube amp to use with the big Pipes for purposes of demo'ing the speakers. They assumed that the VTL Brunhilde monos, a speaker that outputs 750 watts/channel, would be a good choice, but having mediocre output transformers, those amps would not drives the big Pipes. Out of curiosity, and knowing that the 70/70 is a beast (it's totally dual mono, all the way down to dual power cords and dual on/off switches, and has 1-2 Ohm taps), they gave it a try - the 65 watt/channel 70/70 drove the big Pipes beautifully.
The Renaissance amps are special - don't give up so soon.
