After this, the second half output is reversed again, and the two halves are combined in a transformer. So a typical methodology is to use two tubes in a combination called "push-pull", where the top half of the signal is amplified by one tube, and the lower part is reversed and amplified by another. Taking this further, in real tube circuits the curves near the top (saturation) and bottom (cutoff) are seldom this identical. But imagine a situation where the signal is intentionally made so large, that it will be affected by the lower and upper parts of the transfer curve, where there is indeed much more curve! The effect would be to compress the lower and higher parts of the input waveform. Without getting too deep into complex theory, notice that the signal in this case has been "biased" (or positioned) at nearly the straightest point along this curve. Consider this example of one tube circuit's transfer curve. the nearly straight line linearity of most solid state devices, such as transistors and FETs. But the main difference between tubes and the majority of solid state amplification is the non linear transfer curve of a tube, vs. Of course there are many categories of both solid state and circuits that can affect tone and response, not to mention the many variations in speakers and cabinets. Cabinets are not really changeable but different cabinets can be used in different situations, and it's often possible to run more than one cabinet at a time to blend different sounds. open-backed, close-backed, ported)ĭrivers can be and often are switched out.
There are a few amps where the amp class is selectable. In amps with adjustable bias voltages, the power tubes can be swapped for a few other compatible tubes and of course the bias can be adjusted.
Power amp class (A and AB being the most popular by far).So you might have channels with different circuit designs in the same amp, but generally if you want a different preamp sound, you have to buy a different amp.Īspects of power amps that affect the sound include: You can swap out tubes for compatible tubes, with largely subtle differences in final sound. The main aspects of a preamp that affect the sound include:Īll three of those are essentially fixed for a given channel in all but a very few amps. We can divide any complete all-tube guitar amp system into three major sections, each of which has important effects on the final sound: The preamp, the power amp, and the speaker cabinet.Īll tube preamps almost always exclusively use dual-triode tubes that are either 12AX7 tubes or very similar (e.g., 12AT7).
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