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Truth In Car Tube Amp Designs - A Schematic Comparison

"A tube bracketed by semiconductors does not nearly comprise a true tube amp." June, 2006

To deliver the best possible sound quality and reliability in car audio is both the passion and the mandate of Milbert Amplifiers. A decades-long track record, patented designs, sound quality, and legendary reliability affirm this commitment.

Recently, some manufacturers have been putting out what they call "tube" amps, raising the question of what is a true tube amp, or, what role does the tube itself in fact play? The following illustrates the differentiation between employing vacuum tubes for the entire audio signal process (including power amplification) and transistorized designs where the tube(s) do not provide any power output to the speaker.

The Milbert Mobile All-tube Amplifier

Introduced twenty years ago to a stunned mobile audio industry, the original BaM-230 all tube car amp came from the world of high-end home audio. Designed and built for maximum reliability and sound quality without regard for cost, we feel the BaM-235ab continues to set the standard for genuine high-end sound quality and musicality in the automobile.

The patented, all-tube BaM-235ab has ten tubes and zero transistors or semiconductors in its two audio signal paths. All tubes are operated conservatively, with proper, regulated voltages and enormous power reserves. Proven over decades of time, the BaM-235ab design, with its high-end pedigree, numerous glowing reviews, repeat startling performances, and solid history of reliability and unmatched sound quality, remains the world's only all-tube mobile audio amplifier in continuous production since 1986.

Hybrid "tube" amps

Illustrated below is essentially what some manufacturers are calling a "tube" amp -- a hybrid, so to speak, as the tube is simply bracketed by semiconductors (e.g., within a feedback loop) and in fact does not provide any output power to the speaker. This embedded tube basically acts as a token, apparently intending "tonal coloration" but without real power amplification.

"Tube Driver Blue"®

As an example, Butler's "Tube Driver Blue"® utilizes the tube as a low-voltage diode might be and not as an amplifying element (i.e., grid connected to plate). Tubes were invented and used as diodes over one hundred years ago before DeForest and Armstrong recognized their benefits as amplifying devices. See How Tubes Work, Briefly for summary of how space charge produces degenerative feedback, apparently substantive to the diagram below, the patent for which claims, "The new method of utilizing vacuum tube thermionic emissions taught herein to provide a means of variable bias voltage and current for the output transistors greatly enhances the invention... According to yet another important invention taught herein, a vacuum tube with auxiliary illumination is also disclosed." (Trademarks are obviously the property of their respective owners.)


Material herein added and updated constantly; presented for inspirational and educational purposes per Fair Use.

Last modified 18 Feb 2014