Can someone please explain to me what the difference between the two are? Once the signal enters the amp, what does each do? I've got an MPX3 which has one driver and two output tubes. Clueless as to what they do to the signal as it enters from the source and ultimately goes to the headphone out.
dont worry about that, plug your bits into the appropriate sockets and play some tunes.
if it is not good, plug different stuff in.
i would recomend reading the singlepower mpx3/supra tube guides though. it will at least help you avoid some truly doggish combos and terrible tubes in general.
The drive or input tubes amplify the low voltage signal that comes from a sources but this amplification doesn't have much power behind it. The signal is then sent on the a power/output tube that increases the signal from the driver/input tube with regards to power. As an example some tubes can put out 40 watts each as in a KT88. A EL34 will put out around 25 watts depending upon how they are biased, which is a different subject. So the signal now has some real drive behind it. Tube amps are able to put out voltage but lower current. Solid state amps tend to put out lower voltage but have higher current out so they can drive lower ohm speakers/headphones better. It is all a balancing act. I have seen power amps with 12 KT88's per channel, 24 tubes total because not only is voltage needed but current. I like high efficiancy speakers and with these tube amps of low output work great and they don't turn into a heater for the room.
In a single-ended design, we have 3 basic types of tubes; the input tube which does most of the signal amplification, the output tube which powers the speakers or headphones, and the driver tube which drives the output tubes and ensures they're under control.
We need driver tubes since output tubes, especially if several are paired up together will present a reactive load which is hard to drive. They require a fair bit of voltage swing along with a decent amount of current and a low output impedance, otherwise the Miller capacitances and other issues will conspire to roll off the highs and muck up the sound.
Input tubes as a family usually have a fairly high voltage gain, the flipside is their current capabilities are low and the output impedance is high, thus they will have trouble trying to drive an output tube. Look up the specs for a 12AX7 or 6SL7 for example. This is why we need driver tubes, these have a low to medium voltage gain but they have good current capabilities and a low output impedance. See for example the 6BX7 or 12B4A.
In a headphone amp, the input tube often performs driver tube duties as well. In the Singlepower, the input tube, usually a 6SN7, does the voltage amplification as well as driving the output tubes, whatever those may be. Since it's doing the amplification, the sound of the amp will be most affected by the input tube. If you want to blow a chunk of money on tubes, the input is the place to start.
Yes and then you have voltage gain stages and cathode followers (lower output impedence) and other tubes that are a voltage gain stage as a 12AX7 that follows a 12AU7. The 12AX7, 6SL7 has a higher voltage gain but lower current and just the opposite with the 12AU7, 6SN7 and other medium/low mu tubes.
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