This review page is supported in part by the sponsors whose ad banners are displayed below

This overview on the previous page gave us a different perspective on what happened way back then. Nevertheless, it took yet another 20 years before the first 300B saw the light of day. Its initial design and construction method are still in practice today and in increasing numbers even. Contrary to what should be expected, the number of tube manufacturers has risen over the years. Notable is that many tube manufacturers owe their existence to personal conflicts, deceit and the 'borrowing' of designs and ideas.

Back to our quest for why tube rolling creates differences. We stumbled upon another remarkable viewpoint, this time by Eduardo de Lima of Audiopax, a tube maven from Brazil. He is know for his use of pentodes in amplifiers that act and sound like triodes. On the subject of tube rolling, Eduardo theorized and then built up a theory with lots of math to show that the effects of tube rolling amplifiers are based on added distortion! There you have it. Add distortion and it makes its own sauce. Here follows a brief overview of Eduardo's theory.
It is well known that tubes add signal distortion, especially in single-ended circuits without negative feedback. Everyone who reads magazine measurements has seen their high THD figures. By comparison to solid-state amplifier measurements, tube amplifiers seem like utter nonsense and should not even be considered now that transistor amps are
widely available. This conclusion of course is solely based on measurements. How to correlate those to the fact that tube and especially SE tube amplifiers sound so wonderful? Is it because of the clearly measurable distortion being mostly even-order? But why would high THD sound good to the ear? Isn't distortion inherently bad? Shouldn't sophisticated listeners abhor it?
How does the ear measure such distortion? It doesn’t single out the amplifier. It listens to a complete system and how its various components interact. In fact, this includes the recording microphone all the way through the studio recording equipment and pressing plant. And now guess where the very most distortion occurs? At the end of the chain in the loudspeaker. So even if our chain were built up of the lowest distortion equipment possible, it is invariable ‘noised up’ at the end. When loudspeaker distortion is measured, it appears to be predominantly low-order second and some third harmonics. Yet when we measure low-distortion electronics, i.e. non-tube components, their distortion even though low in amplitude is of higher harmonics to which our ears are highly (and negatively) susceptible.


Now Eduardo reminds us that single-ended tube amplifiers also exhibit low-order 2nd and 3rd-order components just like loudspeaker. Hence two distortions interact in a very intimate way. They can either amplify each other, cancel out or anything in-between. The determinant is phase. At 0-degree difference, there is full reinforcement, at 180 degrees, complete cancellation. Any degree between the two extremes will produce partial cancellation and partial amplification.

Eduardo's theory continues from here into complex mathematical terrain but the basic premise is that different tubes generate different distortions at different phase angles, hence interact with the distortion inherent in the loudspeakers they are coupled to and influence the sound that is finally perceived at the ear. The upshot is simply that each and every audio system with its particular assembly of components will react differently. The same tube will have a different aural effect from one system to the next. Isn't this hobby grand?


Against this background, we can now try to make our system -- from source to loudspeaker and room as a whole -- as neutral as we like. The oft-perceived overly warm, romantic and colored sound of tube-based systems is by no means necessary. The trick is in finding the right combination and tube rolling is one of the fine-tuning mechanisms. And it's fun, too.