To buy an argument. Why even consider tubes in a Pre-Amp, as Solid State devices work so much better in low level applications, lower Noise and Distortion, no Hum and no problems with Microphony. I firmly believe that tubes are superior to Solid State in the actual Amplifier Power Output stage, and also by necessity to get sufficient drive to the output tubes. I have just created a superb Commercial 60 Watt Monitoring Amplifier (KT88) for use in Recording Studios etc. It uses solid state Phase Splitter, and common garden variety 12AU7 tubes for voltage gain in the driver section, and for cathode followers. The voltage gain stage has local "Nested" feedback restricting the 12AU7 to a gain of 8. Tested 12 random 12AU7 tubes of various ages and makes in the voltage gain stage, and found a gain difference of less than 0.1 dB, and the plate voltage to come up within + and - 3 Volts of the designed 160 Volts DC. The Amplifier does have Bias Control for adjustment of Output Tube Cathode Current for each output tube, and AC Drive Balance, mainly to compensate for gain differences in the output tubes which despite matching and identical cathode current settings, still have slight gain differences. The Amplifier trims out to give 0.01% distortion at 1 Watt at 1 KHz and at 10 KHz. Changing driver tubes required a slight, but relatively insignificant "Tweak" to get identical performance from every one of the 12 tested 12AU7 tubes. I firmly believe that any healthy tube, of any make, should give identical performance in a correctly designed amplifier. If it does not, the design of the amplifier is suspect. Honestly, valve Pre-Amps, "Forget it", go for solid state any time.
