Vacuum Tube
Audio Equipment for
Cars & Guitars		 
BaM-235ab All-Tube Car Amp • the most musical car amp

The BaM-235ab mobile vacuum tube amp

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. The enhanced BaM-235 followed a few years later. The new BaM-235ab supersedes both. The home audio amplifier that has inspired all three was Stereophile magazine's reference amp for several years. 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.

In June, 2005, The Robb Report magazine wrote in its Great Machines Special Issue, "If musical accuracy is what you are seeking, the Milbert is most certainly the Holy Grail of auto sound."

  Features & Improvements

The BaM-235ab, significantly advances its renowned predecessors.

  • Auto-Plasma-Bias ™
  • Adjustable feedback
  • Selectable grounding
  • Doubled internal energy storage
  • Noticeably improved materials
  • RF design and layout

  • 1. AUTO-PLASMA-BIAS ™

    Output tube bias is sonically important.

    Somewhat like a car's engine idling, output tube bias is a small idling current that keeps the tubes at the ready to respond to audio signals.

    The patented BaM-235ab operates conservatively, runs cool, lasts long, and remains free from audible microphonic noise from vibration. Our tubes last many years, even decades, and are usually changed preemptively by choice rather than technical necessity. This contrasts most tube amps which can be expensive, noisy, wasteful and extremely inconvenient.

    Auto-Plasma-Bias (patent-pending) allows the BaM-235ab to automatically bias itself. Designed and tuned to sound best at its default bias setting, the Auto-Plasma-Bias Point is also user adjustable.

    Auto-Plasma-Bias keeps the output tubes biased properly so they operate and sound their best at all times. Obviating match tubes and manual bias adjustments, Auto-Plasma-Bias automatically adjusts for tube aging and replacement, compensates for imbalances, and adapts to changes in the car's electrical system. In development and testing for several years, Auto-Plasma-Bias is remarkable, fresh and unique to Milbert and now in production.

    As always, the signal path is 100% all tube, and the tube input stages and drivers operate in Class-A mode. In fact, there are ten tubes in the BaM-235ab and zero transistors in its dual audio signal paths.

    An evolutionary step above its two predecessors and built on their twenty-year track record of reliability, sound quality and rave reviews, the first truly "set and forget" tube amp, the BaM-235ab, is the most musical car amplifier.

    2. ADJUSTABLE FEEDBACK

    The BaM-235ab allows operation with or without negative feedback. We think a small amount of feedback is useful, but this is entirely subjective and your system (and ears) may vary. Negative feedback should be subtle and applied sparingly: a good amplifier should work well without any negative feedback to begin with. The BaM-235ab ships with a meager 6dB of negative feedback; whereas, most transistorized or hybrid amps require many times that amount to reduce distortion and prevent oscillation. In the BaM-235ab, feedback is adjusted via a simple jumper, and it can be changed independently per channel. We've not seen this capability elsewhere.

    In fact, removing or defeating the relatively huge amounts of negative feedback in transistorized amplifiers --which are by nature highly non-linear (transistors being inherently semi-conductive switches)-- usually sends them into immediate instability and ultimately self-destruction. In stark contrast, not only can its negative feedback be removed but the BaM-235ab can play into a dead-short without blowing up.

    3. MORE STORAGE + IMPROVED FILTERING

    Radio-frequency designs and more, bigger and better capacitors yield broad sonic and technical benefits. More filtering reduces noise and unwanted interactions among system components while audibly improving performance.

    The BaM-235 already held an extreme amount of energy. A new extreme, the BaM-235ab internally stores and tightly regulates over 100 joules energy (a joule is one watt second of energy). This bottomless energy reserve surpasses and obviates "farad storage caps": It's not just more, it's much more, tightly regulated at ultrasonic frequency, and available precisely when and where necessary.

    4. SELECTABLE GROUNDING

    Installer-selectable grounding circuitry helps reduce ground-loop noise or other system- or installation-specific problems. Yet another useful Milbert first.

    5. TECHNOLOGY & CONSTRUCTION

    We've upgraded technology where it delivers real improvement: ultra high-frequency capacitors, large metal switching transistors (power supply), multi-stage regulation, and custom magnetics. While some of this stuff is rocket science, even seemingly mundane details such as mounting hardware and heat transfer pads are top quality.

    Uncommon materials further enhance performance. Our superior circuitboard material eclipses the overly-touted "mil-spec glass-epoxy" that nearly everyone uses. Truth is, it's tough to find lower-quality material than the industry-standard, so the hype has always been false. The material we use --for its benefit to sound quality-- is thicker, higher-temperature with measurably superior properties and massive copper traces. It's like a car made out of better metal, and it improves everything. Another Milbert first.

    Niceities like durable stainless steel fasteners and hardware, ceramic tube sockets, gold/copper Teflon input connectors, expensive potentiometers, large output terminals, Kimber Kable and Teflon wire were chosen for top quality, reliability and (obviously) never to "save a buck." All pioneered decades ago as Milbert firsts.

    The result is the BaM-235ab, an amplifier not just worth owning but worth keeping. There is an important difference. Many customers have kept their Milberts through several cars. A few have reported their Milberts happily survived wrecks that "totalled" their cars and, in one case, a dune-buggy.

    Top quality parts. Smart, patented designs. Decades of proven performance. Numerous glowing reviews. At this level of excellence every detail matters, and we believe we have them just right. No other car-audio anything that we know of has been in production for twenty years, and we think that this fact alone says quite a lot about our designs and products.

    TIMELESS SOUND QUALITY

    With most everything else becoming generally cheaper and homogenous (including, inevitably, sound), the BaM-235ab is an investment in your aural well-being. In development and testing for five years, we've carefully maintained sound quality and reliability while at the same time advancing state-of-the-art in the current production model BaM-235ab. The BaM-235ab is the most musical car amplifier.

    A BaM-235ab was recently reviewed (June, 2005) by The Robb Report Collection, Great Machines magazine: "If musical accuracy is what you are seeking, the Milbert is most certainly the Holy Grail of auto sound." That's a strong statement and high praise, and we love that part because we feel it commends our ongoing efforts and dedication in bringing reliable, true high-end sound quality into the automobile.

    Plasma Bias, Auto and Automatic Plasma Bias are a trademarks of Milbert Amplifiers.

  BaM-235ab Facts

The patented, all-tube BaM-235ab has ten tubes and zero transistors 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 car tube amp in continuous production since 1986.

Sound & Other Qualities

  • BaM-235ab has 10 tubes, 100% pure tube signal path with no semiconductors.
  • Patented circuitry. High-end audio pedigree. Numerous glowing reviews.

  • Only real, all-tube car amp in the world made and sold worldwide since 1986.
  • Not much stays in production for two decades; we did it right to begin with.

  • 20 years on, we think it still has unmatched sound quality.
  • 25 pounds and shoebox size, it consistently delivers the best sound possible.

  • Impervious to microphonics (noise from vibration).
  • Any audible noise is extremely low, even on sensitive horns.

  • 100% hand-made in USA, highest parts and build quality possible.
  • Proven 10+ year tube lifetimes. Proven stable, durable and road-worthy.

Power Consumption

  • Remote turn-on current draw is approximately 20mA, very small.
  • Idle current is approximately 5A, about the same as one headlight.
  • No special needs or requirements beyond any typical car amp.
  • Regulates and stores over 100 joules of energy internally at high voltage.

Mounting & Temperature

  • Shock resistant neoprene "well-nuts" are provided for mounting.
  • Can be mounted in all but the upside-down position.
  • Heat limiter shuts the amp down at about 100degC.
  • Sturdy, aircraft-aluminum chassis dissipates heat.

Inputs

  • Chassis fuse in negative line; positive line fuse is required near car's battery.
  • Undervoltage lockout shuts the amp down if input power drops below about 10-Volts.

  • Signal input connectors are gold/teflon RCA jacks. 100kOhm input impedance.
  • Full power output (input sensitivity) from 1- to 10-Volts, adjustable.

Outputs

  • Output connectors (and power connectors) are #8 barrier strips, easy to use.
  • Output impedance is selectable among 16-, 8-, 4-, 2-, 1-, and 1/2-Ohm.
  • The amp's two channels may be "paralleled" to double the output power.
  • 30 watts, 2 channels. Can sustain direct shorts --the amp can not be "blown out" in any traditional sense.

  BaM-235ab FAQ

What's the difference between the newer BaM-235ab and the older BaM-235 and BaM-230?
The BaM-235ab offers several substantial improvements, including auto-bias, improved design and internal construction and larger energy storage. The BaM-235ab supercedes both the BaM-235 and the original BaM-230. Upgrades are available.

What's the rating?
30 watts per channel, 20Hz -- 20kHz, -3db, 3%THD Some owners have reported that the BaM-235ab's "30 tube watts sound much more powerful" than comparably-powered amps. This is often attributed to the soft-clipping nature inherent in its design. Unlike transistorized amps which smack into the rails and crackle with abrupt, awful distortion, the BaM-235ab exhibits a graceful, smooth overdrive into clipping. Technically, it's not the same thing as "headroom," but audibly it's much more valuable.

How much current does it draw?
5 amperes at idle, which is about the equivalent of one headlight; 20 amps at full power; the power supply is current-limited to and fused at 25 amps.

How often do the tubes need to be changed?
"Need" is subjective. Some owners elect to change tubes yearly. However, the tubes are operated conservatively and enjoy correspondingly long usable lifetimes: running the original tubes for ten years or more is not uncommon.

What about recent competitors?
The basic BaM-235ab design has been in production since 1986 and is still the only all tube mobile amplifier with proven reliability and legendary sound quality. We predicted at the time it would be the industry standard for 15 years; it remains unequalled.

The BaM-235ab is at ease in the finest high-end home systems. Parts of its audio circuitry have decades-old roots in high-end home audio equipment. It was reviewed by several high-end home audio journals, including the "International Audio Review" and "The Absolute Sound." Car Stereo Review printed, "The Milbert BaM-230 is unlike all other car power amplifiers that we know of." IAR said, "The tube sound qualities of the Milbert really do make an important musical difference, compared to solid state amps. Instruments sound sweeter and more liquid, in a musically correct way. Singers have a richer body to their voice, which gives their lyrics better projection. Music is simply more natural all around...The Milbert won." Stereophile magazine wrote of its home-audio version, "This amp really flies."

Some "tube" amps sport a tube or two inside, apparently tokens attempting to emulate the sound of a real tube amp. They offer nowhere near a track record, appear to be diabolically redesigned frequently, and attempt to conjur "tube sound" through circuit alchemy.

In contrast, the BaM-235ab is an all-tube amplifier with only tubes --and no transistors-- in the audio signal path. This makes all the difference: The BaM-235ab's sound is tube sound, and only tube sound.

The BaM-235ab uses a total of ten tubes to perform all audio amplification. Designed right the first time, it remains true to our original intent of reproducing the best possible sound quality in the automobile.

What's the design history?
The BaM-235ab incorporates audio circuitry that has been used in high-end home tube audio equipment for decades. It is the mobile version of a high-end home amplifier which was J. Gordon Holt's (Stereophile magazine) reference amplifier for several years. We know of no similarly pedigreed mobile amplifier; moreover, now in continuous production for twenty-years, we know of no other car audio anything having a similarly proven road-worthy record.

What's the one outstanding subjective goal?
Musicality: Engaging liveliness with natural and unmistakably, palpably lifelike voices, instruments and music.

What's the one outstanding objective goal?
Reliability. Several customers over the years have crashed their autos (and one dune-buggy) but found their Milbert BaM amplifiers unharmed and still working well. Just imagine our reliability in uncrashed cars.

What about microphonics...in a car, with all the vibration?
Audible microphonics is absolutely non-existent in the BaM-235ab, due to our patented designs and conservative operation. You can shake and jar the amplifier yet not hear a single hint of microphonics.

In fact, people often notice the absolute quietness of the BaM-235ab. Even on sensitive horns, hiss or noise is extremely low, bordering on inaudible.

The BaM-235ab is a stereo amplifier with a total of ten tubes: the entire audio path is tubed; there are no transistors in the audio path.

How long does it take to warm up and play?
Under 30 seconds normally, and up to 60 seconds in sub-freezing temperatures.

How about heat?
Mounting the BaM-235ab in the car's trunk works fine. There's no overheating problem at all, and in fact the BaM-235AB runs so cool that it doesn't even have a fan like other car amps. The heavy chassis acts as the heat sink and remains only warm to the touch. That said, leave enough clearance around the amp above its grill, and do not mount it upside down: There should be some clearance (more is better) around the amp for heat dissipation. The BaM-235ab has a thermal cut-off that will power down the amp if it gets too hot, but we've never heard of a problem from anywhere on the planet in twenty years.

  BaM-235ab Specifications

The BaM-235ab mobile vacuum tube amplifier is not a typical car amp. Its smooth and luscious sound is a delightful relief from typical car audio. We feel that there is no other car audio amplifier in the world that sounds as good as the BaM-235ab.

Its revolutionary, patented design, found in high-end home audio equipment, greatly reduces wasted idling current, heat, and eliminates microphonics (noise from vibration). Dropping or kicking a BaM-235ab while it's playing will not damage it nor reveal even a hint of noise. Its rad-hard vacuum tubes last ten to fifteen years --nearly a decade longer than most home tube amps-- and can even continue playing in the unhappy event of a nearby nuclear blast. See EMP and Effects.

The BaM-235ab's stout power supply stores and recharges over one hundred joules of energy at supersonic frquency, maintaining proper, regulated high voltages even under full load. The BaM-235ab compensates for supply fluctuations and protects against overheating, excessive currents and reverse voltage. It's an excellent power supply.

All component parts have been selected by ear for good sound. The BaM-235ab will supply full power into 16, 8, 4, 2, 1, and 1/2 Ohm and will sustain without damage direct speaker shorts or disconnections, even under full power and for extended periods of time. Its rugged chassis sports high-quality gold/Teflon RCA jacks and #8 terminal blocks to accommodate large spade lugs without disfigurement. A front-panel attenuator adjusts input sensitivity from 300mV to 10Vrms. Teflon-over-copper Kimber Kable is used throughout.

Built for the car yet comfortable even in the finest home or studio audio systems, the BaM-235ab is one tough amplifier with finesse. At last, true high-end, home-quality sound for the car.

Size and weight: 4.5 in. H x 18 in. W x 6.75 in. D; 15lbs.
Power consumption: 5A at idle (no signal); 20A at full power
Power output: 30wpc into 16, 8, 4, 2, 1, 1/2 Ohm
Frequency response: 20Hz -- 20kHz -3dB
Hum & noise: -90dB from 20Hz -- 20kHz (unweighted)
Warranty: one year parts & labor; return freight paid

  BAM-235ab Purchasing & Upgrade

The BaM-235ab is available directly from the factory and from authorized dealers worldwide: Call or email.

An upgrade is available for BaM-230 and BaM-235 owners. It's a substantial upgrade that involves changing almost everything inside including the tubes, sockets, power supply, etc. It's nearly a new amp. If you have a BaM-230 or BaM-235, this upgrade brings your amplifier up to newest specification and performance. The attendant improvements are definitely worthwhile. Call or email for details.

  BaM-235ab Press & Reviews

From The Robb Report Collection

Automotive Audio: Tubed Tunes on the Go
Jeff Dorgay 06/01/2005

Milbert BaM-235 Car Amplifier
Many of today's mobile audio magazines feature rock stars and athletes who have invested the equivalent of a sizable down payment for a second home in their automotive playback systems. Most of these offer multiple large amplifiers and gigantic woofers, capable of achieving earsplitting sound pressure levels. Unfortunately, when compared to even basic home hi-fi systems, they often fall woefully short in fidelity. However, there is an alternative approach. Maryland-based Milbert Amplifiers handbuilds vacuum tube–powered car audio amplifiers that are similar in approach to the best audio amplifiers designed for home use. Rumor has it that Eric Clapton has a pair of Milberts in one of his favorite cars.

Milbert's recent amplifier, the BaM-235, is an evolutionary design that steadily improved over 19 years. The stereo power amplifier, which is built to military specifications, generates 30 watts per channel and can be bridged to be a single-channel monaural amplifier capable of 60 watts. Just remove the cover to reveal the same high- quality components you would find inside an amplifier from Audio Research or Krell. Thanks to a new auto-biasing circuit, the output tubes will never need adjustment during their 10-year lifespan.

Skeptics might be wary of the durability of vacuum tubes when used in an automotive environment, but Michael Milbert assures that I could dropkick the BaM-235 while in operation without affecting performance. While I did not take this extreme, a drive on the most tortuous roads in my BMW equipped with aftermarket (i.e., stiff) sport suspension did not affect the system's performance in any way. Anyone installing a Milbert in a luxury car should have no worries at all.Because an amplifier designed with vacuum tubes has a much gentler distortion characteristic than a solid-state amplifier, such amps tend to sound louder—per watt—than transistor amplifiers. Don't be fooled by the modest power output figure of the BaM-235. With a pair of very accurate two-way speakers and a modest subwoofer, a system built around the Milbert will outperform one of those big multiamplifier systems. If musical accuracy is what you are seeking, the Milbert is most certainly the Holy Grail of auto sound.

At $2,995, the Milbert BaM-235 carries a very high price per watt, but considering its sublime performance, it is one of the best buys in car audio today.

Milbert Amplifiers, 301.963.9355, www.milbert.com

BaM-235ab press releases also appear in 12volt News, Celebrity Car magazine, Enjoy The Music, 21 HiFi, and others as well as various sites and forums online.

  • Related Reviews:
    • The Robb Report Collection, "Great Machines," June, 2005 "...Milbert is most certainly the Holy Grail..."
    • The Absolute Sound magazine PDF "...Milbert...soundstage in the car is uncanny..."
    • International Audio Review PDF "...the Milbert won..."
    • Car Stereo Review magazine PDF "...Milbert...is unlike all other car power amplifiers..."
    • Car Audio and Electronics magazine PDF "...Milbert tube amp...you just can't beat the sound..."
    • Soundslike magazine PDF "...simply more pleasant to listen to..."
    • AutoStylin magazine PDF HTML "Nothing can beat this amp."
    • snippets & quotes

    •   BaM-235ab Press Release

    For immediate release:

    Germantown, MD, June, 2005, Milbert Amplifiers introduces its BaM-235ab car tube amp, the evolutionary third model in its 20-year-old line of automotive vacuum tube amplifiers, which offers several improvements including patent-pending "auto-plasma-bias" (TM) circuitry which Milbert claims adapts to music levels and maintains proper bias at all times while also automatically compensating for tube aging and obviating any need for using matched tubes or manual tube bias adjustments.

    According to Milbert, other improvements in the BaM-235ab include radio-frequency layout and design techniques, additional energy storage, adjustable feedback, adjustable grounding, and "above-mil-spec" circuitboard material that is thicker, able to sustain higher temperatures and carry more current than standard "glass-epoxy." Christopher Milbert explains, "it's like a car made out of better metal, and it improves everything."

    "BaM car tube amps have always been impervious to microphonic noise from vibration," continues Mr. Milbert, "and they also offer ten-year-plus tube lifetimes --practically unheard-of in home or studio, and definitely unique in the harsh car enviroment. With a high-end home audio pedigree and numerous strong reviews and industry awards, the BaM sound quality is renowned. Automatic Plasma Bias, adjustable feedback, adjustable grounding, improved layout and more energy storage --all of which provide real and audible benefit-- result from our ongoing honing and improvement of our classic tube car amp, now available in its third and newest incarnation, the BaM-235ab."

    Based largely upon its predecessors yet recently reviewed as "most certainly the Holy Grail of auto sound," the 30-watt-per-channel stereo BaM-235ab uses ten vacuum tubes, class-A input stages, an 100% all-tube audio signal path, and patented designs to eliminate microphonic noise from vibration and maximize sound quality.

    Milbert Amplifiers has been building vacuum tube car audio equipment just outside of Washington, DC since 1986, with its single model car tube amp (in three consecutive versions) in continuous production for nearly twenty years. The BaM-235ab is available directly from Milbert's website or from dealers worldwide.

    Press pictures and details available at milbert.com/BaM235ab

    Large promo photo: http://milbert.com/BaM235ab/BaM235ab-TubesGloves-300d.jpg
    Product photo 1: http://milbert.com/BaM235ab/press/BaM-235ab-1.jpg
    Product photo 2: http://milbert.com/BaM235ab/press/BaM-235ab-2.jpg
    Product photo 3: http://milbert.com/BaM235ab/press/BaM-235ab-3.jpg

      BAM-235ab Owner's Manual, Notes and Technical Support

    A comprehensive Owner's Manual is available online for Registered Owners. Please register and login for access.

    Technical Notes are available online for Registered Owners. Please register and login for access.

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