Future of Tubes is TODAY

[Chuck H]

A solid state device requiring a heater?

I'll wager the heater voltage is rectified, regulated and used in some other non filament capacity inside the "toobs".

(As they should hensforth be known so that we may differentiate them from "tubes" without having to say "amt tubes" or "transistor thing in a tube shaped case that fits a noval socket" )

[nickb]

I use what this patent calls prior art. FIELD EFFECT SEMICONDUCTOR DEVICE HAVING AN UNSATURATED TRIODE VACUUM TUBE CHARACTERISTI
As far as I know, nobody makes the parts that would be covered by the patent.

The parts I have are tricky to bias, you need an opamp to force them to behave, but it works flawlessly. I couldn't have done this without my trusty Tektronix 576 curve tracer. The only parts I use that were not available in the 1980's are the output transistors.

Anybody in the Dallas area PM (not email) me and we can setup a demo. Bring your camera.

Well do tell us more...

[tedmich]

I'll wager the heater voltage is rectified, regulated and used in some other non filament capacity inside the "toobs".

pretty LED!!

[carlg]

I use what this patent calls prior art. FIELD EFFECT SEMICONDUCTOR DEVICE HAVING AN UNSATURATED TRIODE VACUUM TUBE CHARACTERISTI
As far as I know, nobody makes the parts that would be covered by the patent.

The parts I have are tricky to bias, you need an opamp to force them to behave, but it works flawlessly. I couldn't have done this without my trusty Tektronix 576 curve tracer. The only parts I use that were not available in the 1980's are the output transistors.

Anybody in the Dallas area PM (not email) me and we can setup a demo. Bring your camera.

Sounds interesting. This patent is about the VFET (or SIT) devices Nelson Pass discusses in that link above. NOS pieces were still available until quite recently, but they were getting very expensive, like $40 a piece.

[Chuck H]

pretty LED!!

I actually thought that was a nice touch.

It's pretty damn easy to demonstrate how your transistor reacts very "similar" to a tube with the same power supply and power amp sag applied to both UNTIL YOU START CLIPPING THEM!!! That's when things get real. Show me the clipping characteristics of these devices compared to tubes in the same environment. If their at all similar, then I'll be impressed. It's too easy to fall back on common audio "standards" when it comes to presenting a product like this because that's all that's ever been offered for tubes as well. Tubes went out of tech at a time when clipping the amplifiers wasn't the goal. This makes a modern comparison based on antique standards a cake walk. I'll need a real life "as used in a guitar amp" comparison that includes every drive level. If it's at all "similar" under these conditions, then I'll try them.

[carlg]

Absolutely agree, that's pretty much the entire point yeah? But if you think there's some type of "magic" happening with a clipping tube that can't be clearly understood and reproduced then I'm not with you on that. Electronics is math, pure and simple. It's not powered by magic. It's all measurable, explainable and reproducible. Maybe not by me in my tiny little shop!, but the things electrical engineers have managed to build at this point in history SO wildly eclipse the job of reproducing a humble 12ax7 that it makes no sense to imagine the 12ax7, of all things, is an impossible challenge. I mean, ICs can easily have 3 million components in them. A 12ax7 does something nice with only a single component and there's a romantic quality to that, but come on, the EXACT same clipping behaviour has to be possible to reproduce when you have 3 million components at your disposal that can be arranged with computers and punched out for fifty cents a piece. It's only a matter of paying someone who knows more about electronics than leo could have ever dreamed of to get the design done. If you're a billion dollar company that seems very achievable, so I have to say again this seems much more like a marketing direction than a technical one.

[GainFreak]

It's pretty damn easy to demonstrate how your transistor reacts very "similar" to a tube with the same power supply and power amp sag applied to both UNTIL YOU START CLIPPING THEM!!! That's when things get real. Show me the clipping characteristics of these devices compared to tubes in the same environment. If their at all similar, then I'll be impressed.

From what I know these AMT "SS tubes" were developed and marketed to be direct replacements in guitar amps so they would behave as tubes not only with clean HiFi audio but will have the same clipping behavior otherwise what's the point.
Only an A/B test will prove if this is so or not.

[teemuk]

Don't know about these AMT "WarmStones" but when the similar RetroValve / Jet City product got on discount they started to sell like hot cakes. On a certain forum they were momentarily the "flavour-of-the-week" -product and about everyone's experience was that they were as good as generic vacuum tubes they replaced, with the exception that they don't wear out and travel more safely as backups in a gig bag. But if the price is too high no one buys them and we only get the opinion of prejudiced people who never even try this type of stuff in the first place.

Yes, the modern SS tube replacements try to more realistically mimic a vacuum tube, including all characteristics that could be considered "flaws". It's a new approach to initial mindset of replacing the vacuum tube with a solid-state device that performs better than the tube. For example, Fetron's, althoug commonly a substitute for triode tube, were actually designed to mimic pentodes because pentode characteristics offered more efficiency than a triode. Their designers would have laughed at concepts like deliberately mimicking triode-like distortion or clipping characteristics. Today they are quite well researched topics and we have very genious engineers that develop solid-state circuitry that nails characteristics of particular tube type to very close detail, likely in about same tolerance as generic vacuum tubes coming from different manufacturers.

In the end my ears don't really care whether electrons genuinely flom from cathode to plate or whether there's a complex integrated circuit and solid-state electronics involved in processing the audio signal, as long as outcome is the same.

[Chuck H]

Well, here I'm going to treat ya'll to the ramblings of an experienced layman observer without all the tech to satisfy questions.

What I've seen as the primary problem facing the guys that want to turn transistors into more tubey sounding circuits is that the two different amplifiers require different support systems. The higher voltage and lower capacitive power environment that tubes operate in responds differently to current demands than do power supplies appropriate for transistors. At face value this seems like it would be easy enough to replicate, but as it happens, not so much. The differences compound into "responses to responses and so on" by the two devices question. Differences in power supply impedances and time constants for the two circuits breaks down into managing those anomalies in the signal chain and then how it again affects the power supply. At face value this seems like it should be manageable, but it's not. You can't just build a power supply with same failings or advantages and expect it to respond to all circumstances the same because, again, the devices don't operate exactly the same. To me this seems horrifyingly daunting. Which is probably why the approach so far has been to analog model what seems like the most important audio anomalies. Like an impressionist painting of an image. Or to digitally sample them. Like a photo would be as compared to looking at the real thing. Both these approaches fail to make the actual amplifiers react in kind to the actual operating environment. Which is probably why they'll never sound just right. The action/reaction and response of all the circuits needs to be an actual, rather than simulated affect to sound natural. Maybe.

EDIT: I just wanted to add that I think creating actually analogous responses between tubes and "toobs" should be easier in the class A environment of the preamp. Except that the behavior of a preamp tube operating at, say, 200V at idle and then how it changes at only 150V when the amp is loaded is a real problem because a transistor responds differently to a variable voltage environment and that again changes how the amp is loaded and now we're back into an avalanche of different reactions.

[uneumann]

Well, here I'm going to treat ya'll to the ramblings of an experienced layman observer without all the tech to satisfy questions.

What I've seen as the primary problem facing the guys that want to turn transistors into more tubey sounding circuits is that the two different amplifiers require different support systems. The higher voltage and lower capacitive power environment that tubes operate in responds differently to current demands than do power supplies appropriate for transistors. At face value this seems like it would be easy enough to replicate, but as it happens, not so much. The differences compound into "responses to responses and so on" by the two devices question. Differences in power supply impedances and time constants for the two circuits breaks down into managing those anomalies in the signal chain and then how it again affects the power supply. ...

The action/reaction and response of all the circuits needs to be an actual, rather than simulated affect to sound natural. Maybe. ...

Fully agree with your ramblings, Chuck... shifts due to power supply are important, and so are shifts due to most all the coupling and bypass caps in the circuit. The open loop nature of tube circuits allows these to arise and ripple throughout an amp and produce a "springiness" that's unique and hard to capture and emulate in SS systems. One point I want to make though - and that is there is no one "magic" response or tube characteristic. There is no point in *EXACTLY* simulating or reproducing any one tube or complete amp system. Every tube you buy has tolerances and there are plenty of tube amp circuit variations out there that sound good. So it seems clear that a wide range of "tube effects" work well. Exact reproduction of any component or subsystem doesn't seem to matter. That means non-tube systems have plenty of room to produce similar (not-exactly the same) but still good sounding systems.

[mhuss]

Transistors schmansistors - soon it will be all software-based with very accurate (and continually improving) modelling going through FRFR amps and speakers. Look at the Kemper (aka "the devil's toaster" ) or the new BiasFX box. Maybe they're not quite 'there' yet...maybe. But every year they get an order of magnitude better. How soon before it's impossible to tell the difference in a double-blind test?

I build tube amps and am part owner of a company that sells tube amps, but as an ex-programmer, I'm seeing (hearing?) the writing on the wall.

[bea]

While this is technically correct, i do not believe that tubes will die, at least soon.
First thing: longevity. Tube amps have the potential to be usable or reparable over several decades (older, discrete transistor amps as well). Will the modern stuff survive, say, 15 years?
Tube amps are "stylish" - old technologie, yet fascinating also younger people, relatively easy to understand and to build.

[mhuss]

Theoretically, this is true. But (for example) try to find a replacement power MOSFET for an amp from the 80s. Or, try buying NOS beam tubes (KTs or say, ECG Phillips 6CA7s) - again, almost extinct, and priced accordingly. It's a good thing we all use 12AX7/ECC83s, else there wouldn't be enough market to make and sell them. I'm not giving up on tubes yet, but I see the future, and it's ... different.

[bea]

A problem i am well aware of - two of my amps use ECC808 in the input stages...

But at present there are plenty of rebuilds of more than the standard types available.

[loudthud]

Well do tell us more...

There are certain unwritten rules that most solid state designs follow. (Group Think) My design breaks most of them. If the design was sold to an amp company, they would try to "improve" it and totally kill the magic. One of the rules that Juan likes to tout is that you should never drive the power amp to clipping. My design slams the rails and makes the power supply sag. That's part of the magic. That's where the FEEL of a tube amp comes from. As good as Juan's amp sounds in the video he recently posted, I'm not hearing the tube amp feel in the clip. It could be that I need to be in the same room with the amp or actually play it to see how it feels. You can't really tell much from videos posted on the internet. Would you buy a car on the internet?

Link to Fahey amp video, post 19: http://music-electronics-forum.com/t41444/

But my design suffers from many of the limitations of a tube amp. Crank the Master Volume down to bedroom levels and it doesn't sound as good, it looses the feel, just like a tube amp. Because you can overdrive the power amp input, there is not as much gain available as you turn the Master Volume down. You can crank the line voltage down to about half (1/4 power) and it sounds ok.

I looked at every JFET I could get my hands on. The ones that behave the most like triodes are switching JFETs operated well below Idss. These JFETs are fairly low noise. I did lots of experiments to find ways to bias them. Some biasing methods are discussed in this thread: http://music-electronics-forum.com/t39927/ Some of the things I tried were rejected because they didn't track the power supply, required a trimmer pot, or just plain sounded bad. Some of this was discussed on SSGuitar forum. Link: Look Ma, NO POTS! I eventually settled on two designs, one for the first stage that has the same headroom of a 12AX7 and a second stage that has more gain. Grid current simulation is accomplished with diodes. With these building blocks I made a Blackface Fender preamp and a 5F6A dual channel preamp.

The power amp is a whole nother can of worms. Over the years I built quite a few. The design I'm using is deceptively simple. It uses only 5 transistors, it has a gain of 100, no AC feedback, the input impedance is 220K, output impedance (not load impedance) is about 45 Ohms and it produces a non-symmetrical square wave when over-driven. Lots of even order distortion. It produces 50W at 4 Ohms and is loud as hell when it's slamin the rails. What got me started on this design was a thread on DiyAudio about building a power amp into an Altoids tin. This thread also provided inspiration: Tube sound from a transistor amp, it's possible - diyAudio but in the end, Nelson Pass played the biggest role. I have 97 posts in this thread: Amp Camp Amp - ACA - diyAudio but I used a class AB output stage.

Some people that played the 5F6A amp wanted more gain so I installed a switch that lets you place the two input channels in series. In that mode the overall gain with all the pots maxed is about 100dB. Overall 12 transistors and 3 opamps. The opamps and 3 of the transistors are not in the signal path.