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WRGKMC

Transformerless Tube Amp????

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I was looking for info on magnetic compression created by tube transformers and stumbled upon an amp design that uses tubes with

no output transformers and therefore has no coloration caused by the transformers inductance. as a bonus the amps will use just about any

power tube and have no speaker impedance limitations.

 

Because I'm an electronic tech this does sound like Voodoo magic to me. I need to find more information on it before I'd consider it

a good alternative to a traditional tube amp. Something must convert the high voltage, Low current from a power tube to low voltage high current.

We all know its the current that makes the speaker coils move, not the voltage.

 

I first found this article about the negative side effects of a tube transformer. http://milbert.com/tubes_vs_transformers

 

It has some valid points but its obviously written by someone who goes way overboard evoking science fictional magic mixed in with facts to hype the

design way beyond what's needed. When someone attempts to bash one technology to promote another it sets up red flags on my radar.

 

It may appeal to non technical types who are often willing to not only purchase snake oil but actually drink it, but its only going to alienate educated

electronic techs and engineers like myself who would normally promote new technical designs. We may find stuff like UFO's and Chariot of the Gods interesting

to ponder but we do need hard proof that isn't laced with snake oil to sway people into believing something's revolutionary. After all the laws of physics are based in truth, not fiction.

 

Here's one of the amps this company makes. http://milbert.com/gaga/?db=1

I'm still looking for some actual technical description one what's used to convert the high voltage to high current.

 

If a transformer isn't used then what is?

 

 

 

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... If a transformer isn't used then what is?

 

I'm super skeptical about this. My guess is that the 'tube amplifier' goes to a resistive dummy load and is then capacitor-coupled to a clean solid-state power amplifier. "Tube tone" is not necessarily tube POWER. The fact that the amp accepts "any speaker load" and has the same power rating(s) regardless of the tubes used makes me believe tube part is a basically a preamp that uses power amp tubes and that it's actually a very clean solid-state amp that pushes the speaker.

 

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Did a little more digging and found the patent. http://www.freepatentsonline.com/5612646.pdf

 

I suspected snake oil was at the heart of all the matter. Miller must be smoking diodes if he expects others in the industry to believe his claim in having a Transformerless design. That's about as close to claiming perpetual motion as you can get. No competent tech is going to believe those kind of voodoo statements and when people stoop to those tactics its usually to promote something that needs people to believe its something its not.

 

The amps do use transformers like any other high voltage amp. The only significant difference is the hybrid design. Many hybrid amps have solid state preamps and power tube outputs. This amp just does it in reverse. They use wide frequency transformers and put Mosfets after the transformer to drive the speakers. This really isn't any different then many Mosfet amps. Vox in fact uses something similar.

 

Sunn used this output design back in the early 70's in their Concert Lead amps using a transformer and Fets to mimic power tubes.

 

3YoNh.jpg

 

The thing is, any power tubes used in this amp are simply act as "preamp" tubes and not power amp tubes.

 

Its always the last stage of amplification that signifies what kind of amp it is. This one is just a little unique because it allows a great variety of preamp tubes to be used. The only other question that I couldn't tell from the schematic, was whether the tubes actually do run on high voltage or weather they are just another starved voltage design someone sticks an LED in back of the tube to make you think its running one high voltage.

 

Beyond that, the amp may actually sound great, but why hype it with half lies if it does sound good? Mosfet amps do sound great but you aren't going to convince tube lovers its anything more then it actually is, A SS hybrid. Bashing vintage tube designs in attempts to belittle their quality in order to promote your own design, no matter how good that design is isn't going to develop much respect .

 

There's a big difference between an advertisement that says clean tones move faster through the air. People get that joke. Washing the car cuts down on wind friction right? Using fact and fiction together to twist facts like that only makes working in this industry harder for everyone because you do find idiots who actually believe that crap. There's enough false info to deal with without intentionally drumming up half truths to promote sales.

 

The real facts on transformers are explained well here. http://education.lenardaudio.com/en/14_valve_amps_5.html

Edited by WRGKMC

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after reading your first post i thought without a patent number and not being able to review the patent description it can only be snake oil.

now with the information from the patent its just false advertising :)

 

first i thought maybe they invented something like the inverse of a switching power supply to get rid of the transformer, which itself sounds too good to be true, now its just some tube driver mosfet power amp whcih sounds really boring :D

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A tube requires 12 volts on the heaters and a lot more on the plate to function properly. Somehow those voltages have to be "transformed" and I doubt it's with resistors. I actually saw an amp design that used all transformers instead of coupling caps and resistors. That looked ridiculously complicated as it was.

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A tube requires 12 volts on the heaters and a lot more on the plate to function properly. Somehow those voltages have to be "transformed" and I doubt it's with resistors. I actually saw an amp design that used all transformers instead of coupling caps and resistors. That looked ridiculously complicated as it was.

 

They say no OUTPUT (speaker) transformer. It's very possible to couple the A.C. audio component of the signal coming off of a tube plate with a capacitor and amplify that signal with a solid-state amplifier. A capacitor will block the high B+ voltage but allow the AC audio through.

 

Of course it will need a transformer (or switchmode power supply) to provide the voltage for tube heaters.

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IIRC back in the 60's a bunch of "transformer-less" tube amps came over from Asia. Most of them caught fire, many of them burning down houses. I can't remember the details, but I believe UL/CSA refused to allow them to be sold after a while because they were considered so dangerous.

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Sorry to revive an old thread, but I might be able to add some clarity to this subject.

 

Transformerless tube amplifiers do in fact exist, and are among the most highly respected audiophile amplifiers in existence. I've had one since roughly 2003, a US Amps TU-600, that is by far the best sounding automotive amplifier I have ever heard. One of the most respected home amplifiers of the current era, the Tenor 350M, also uses the same topology.

 

As someone above mentioned, the trick with a tube is that they are incapable of amplifying current, as current can't jump the gap in a vacuum tube. What they are extremely good at is accurately amplifying voltages, and they can perform large amplifications in a single stage, whereas solid state amplifiers need a cascade of transistors to achieve this. The two amplifiers above use tubes to amplify voltage, then a solid state "following circuit" to apply current without using a transformer.

 

The main benefits of this design are that it reduces the number of components in the signal path, and allows for the elimination of an Automatic Gain Control (AGC) circuit. An amplifier without an AGC is sometimes referred to as a "single ended" design. For those not familiar with it, an AGC is required in solid state amplifiers to keep the cascade of transistors from destroying themselves if too large of a spike appears in the input signal. The unfortunate side effect is that an AGC is effectively an input driven variable compression circuit, and it is always active to some degree, which takes the teeth out of transients.

 

I can tell you from experience with the US Amps design that is does not sound even remotely "warm" or "mellow". It is the most ruthlessly accurate amplifier I have ever heard, and provided a kind of attack on transients I didn't even know was possible. I went from a vaunted McIntosh MC431 to the TU-600, down over 100 watts in rated output, and it sounded as if I went up in power by a factor of 2. The first time I listened to it, the first snare shot actually made me flinch it was so in your face. Totally blew my mind.

 

So, it is certainly possible. I can't comment on whether the OP's mentioned design is correctly executed or not though.

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Hate to bust your bubble but the US Amps TU-600 is not a tube amp, its a Hybrid.

 

It uses a couple of preamp tubes run at very low voltages to give the signal some tube tone. They don't actually amplify anything.

 

The amplification is 100% solid state from there on so other then some crappy tube coloration (and it is usually crappy at low voltages) its essentially a SS amp.

 

And by the way it does use a transformer. That big donut in the center of the circuit board is a toroidal transformer likely used to step the current up for all those output transistors.

 

http://i754.photobucket.com/albums/xx187/n2bmrs97/IMG_0517.jpg

 

 

There's allot of these low voltage tube preamps being sold in pro audio. They are no more then snake oil designed to rip off low information buyers.

 

Cars did use all tube radios when I was a kid. Some actually sounded great. The tubes were specialized for that job and they ran on much lower plate voltages. They didn't put out more then a watts or two, but that's all you needed to run a dash board speaker that reflected the sound directly in your ears. They did use transformers for stepping up the plate voltages and an output transformer to match the speaker impedance. (I used to repair them when I first became a tech)

 

They used to make portable tube radios that ran on batteries too. They used a low voltage (usually 6V) battery for the heaters. Then they'd used something like a 36V battery for the bias voltages. The 36 V battery simply contained a bunch of small 1.5V in series to add up to the plate voltages needed.

 

The bias voltage doesn't require allot of current, usually in milliamps so the batteries usually lasted quite awhile. The output transformer was used to convert the high voltage to high current needed to move the speaker's electromagnetic piston.

 

The thread was about high wattage Pro Audio gear however, specifically guitar amps running off a wall outlet, and specifically the output transformer that moves the speaker. You need high current to move an electromagnet.

 

Tubes run on high voltage low current. A step down transformer isn't the most efficient device made for that change but its still the best thing made for the specific tubes still available. Tube technology is essentially a dead technology. Unless someone was investing big bucks in R&D designing new tubes you aren't going to see any changes to the transformers used to drive speakers. We already have transistors that do that job and they are by far more profitable.

 

You can take enough batteries and string them together and operate a tube amp without its AC transformer. You only need about 15, 12 volt batteries (Preferably wet cell batteries that can be recharged) It just isn't the best option for a musical band. You'd still need an output transformer to convert the high voltage to high current with tubes to drive the speakers. Transistors are by far much more efficient and light weight because you aren't converting to high and low voltages. Transistors run on DC and can drive speakers directly without a transformer.

Edited by WRGKMC

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On 6/1/2017 at 6:05 PM, 1001gear said:

Skewz me. You are describing car audio?

Sorry to revive a zombie thread, I just stumbled across this again.  Amplifiers are amplifiers.  Some are specialized for different purposes of course, but they still do the same job.

 

On 6/1/2017 at 11:13 PM, WRGKMC said:

Hate to bust your bubble but the US Amps TU-600 is not a tube amp, its a Hybrid.

 

It uses a couple of preamp tubes run at very low voltages to give the signal some tube tone. They don't actually amplify anything.

 

The amplification is 100% solid state from there on so other then some crappy tube coloration (and it is usually crappy at low voltages) its essentially a SS amp.

 

And by the way it does use a transformer. That big donut in the center of the circuit board is a toroidal transformer likely used to step the current up for all those output transistors.

 

http://i754.photobucket.com/albums/xx187/n2bmrs97/IMG_0517.jpg

 

 

There's allot of these low voltage tube preamps being sold in pro audio. They are no more then snake oil designed to rip off low information buyers.

 

Cars did use all tube radios when I was a kid. Some actually sounded great. The tubes were specialized for that job and they ran on much lower plate voltages. They didn't put out more then a watts or two, but that's all you needed to run a dash board speaker that reflected the sound directly in your ears. They did use transformers for stepping up the plate voltages and an output transformer to match the speaker impedance. (I used to repair them when I first became a tech)

 

They used to make portable tube radios that ran on batteries too. They used a low voltage (usually 6V) battery for the heaters. Then they'd used something like a 36V battery for the bias voltages. The 36 V battery simply contained a bunch of small 1.5V in series to add up to the plate voltages needed.

 

The bias voltage doesn't require allot of current, usually in milliamps so the batteries usually lasted quite awhile. The output transformer was used to convert the high voltage to high current needed to move the speaker's electromagnetic piston.

 

The thread was about high wattage Pro Audio gear however, specifically guitar amps running off a wall outlet, and specifically the output transformer that moves the speaker. You need high current to move an electromagnet.

 

Tubes run on high voltage low current. A step down transformer isn't the most efficient device made for that change but its still the best thing made for the specific tubes still available. Tube technology is essentially a dead technology. Unless someone was investing big bucks in R&D designing new tubes you aren't going to see any changes to the transformers used to drive speakers. We already have transistors that do that job and they are by far more profitable.

 

You can take enough batteries and string them together and operate a tube amp without its AC transformer. You only need about 15, 12 volt batteries (Preferably wet cell batteries that can be recharged) It just isn't the best option for a musical band. You'd still need an output transformer to convert the high voltage to high current with tubes to drive the speakers. Transistors are by far much more efficient and light weight because you aren't converting to high and low voltages. Transistors run on DC and can drive speakers directly without a transformer.

Again, sorry to revive an ancient thread.  I guess I forgot to click the notify button last time. 

 

We could go round in circles on the semantics of tube amp vs tube hybrid all day.   You could call it a tube hybrid, but most amplifiers referred to as tube hybrid do not function in the same way.  Most are what is referred to as a "tube-preamp", where the tubes just step up in input voltage to what amounts to an otherwise normal, solid state amplifier. 

 

The designs I mentioned are not related to the "tube-preamp" style that people are used to seeing, though.  The big change in the amps mentioned is that the solid state output stage does not function like a normal solid state output stage.  It isn't actually amplifying the voltage of the signal, just the current.  They essentially replaced the output transformer with a solid state circuit that does not step down the voltage in order to convert it to current.  Instead it passes that voltage along cleanly, and adds in the matching current to follow the input signal.  The main benefit is the elimination of the coloration and damping effect of the transformer, though in the case of a guitar amp, there are obvioous other practical benefits such as the removal of a huge chunk of steel and the associated weight.  

 

They are not using the tubes to "color" the sound in this case, they are using them for their accuracy, and ability to limit the number of components in the signal chain. 

 

An interesting side note, is that in the TU-600 at least, this enabled them to eliminate the AGC circuit.  AGC, short for Automatic Gain Control, is basically a feedback elimination loop circuit that attenuates the input when the output starts to get too high.  Solid state amps are prone to what is called a cascade effect overload.  The long chains of transistors, each amplifying the signal from the former and passing it on to the next, can sometimes run amok when too large an input signal is applied, and end up destroying the weak link in the chain.  The AGC is like a compression circuit, that cuts the peaks down to prevent an overload.  Unfortunately, this also limits dynamics.  Elimination of the AGC yields an amp with much more impressive attack and dynamics.

 

Again, sorry for the zombie thread, I just came across this again today while looking for something else.  

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personally i find no fault in zombie thread resurrection when pertinent or new information is brought to light...   rather than “LOL” and a smiley...  

thanks for the info...

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