1) There are only 14 volts across the plates of the tube. According to my friend, something like 300 volts is required to make it act as a tube should in the circuit if it were going to have any effect.
This is both an incorrect measurement/value and an incorrect understanding of tube theory.
Firstly, the
MAXIMUM from cathode to anode when the tube is in
CUTOFF is ~300 volts. In this condition the tube will
not pass signal).
Secondly, the load line and transfer function curve spans from zero volts to 300 volts with varying grid bias and plate currents. Linear operation can occur at any place along the valid curve. How linearity is managed depends on the circuit design, local feedback, and what the designer intends the circuit to do in both the linear as well as the non-linear range. Under "ideal" conditions for maximum VOLTAGE gain, the plate is generally biased at around 150 volts in the highest (safe) voltage circuit. Without delving into propriatary design information, the theory of relativity applies here as well... what the plate and bias are relative to is critical to understanding any circuit.
I designed the circuit to be relatively insensitive to the possibly wide variations in tube parameters and aging. Once we developed the sound/feel that we desired, we wanted this to be consistent over a reasonably wide range of tube parameters that occur during the manufacturing and grading process. Critical parameters can vary by as much as 100%, so why should some customers receive amps that are "worse" that other customers when we have some control over this in the design process?
2) The grid is wired to the cathode. The plates are out of the circuit and have no effect on the sound. There is no gain generated by the tube.
This is also incorrect. I suggest that your friend remove the tube and confirm his incorrect assumption. Perhaps he may have an incorrect pinout of the 12AX7 or is looking at the pinout upside down. There is a voltage to current to voltage function going on that he is missing. This is critical to the feel and quickness at low frequencies.
The tube is one component of the overall sound and performance of the ENTIRE amplifier. The circuit is designed specifically to be responsive for bass players needs, to exhibit low microphonics under the high vibration environment of bass amplification. Additionally, unlike a guitar amp, the overdrive characteristics necessary for bass applications requires a little different (though classical) approach to the design. We built up many different tube circuits and this is the one that was most preferred for sound and feel.
If any of you know how to verify this please let me know. I really want to like this head but am starting to feel like I bought something that is more hype ( look it has a tube!!! ) than actual engineering.
Either you like the amp or you don't. I personally assure you that plenty of actual engineering and play testing went into the design decisions for all signal paths. I am also an electrical engineer with over 25 years designing products for the pro audio, guitar and bass amplification industries. I also have plenty of pro audio touring/support experience. The rest of the design team has just as much experience in their respective areas.
johnny a. staind
