Solid-State TUBES !!

[GlennSprigg]

A lot of places are now developing Solid State 'Tubes', although with no need for a vacuum inside.
We are not talking about modified circuitry to change over to semiconductor equivalent circuits, but a solid state construction that is inside of a glass envelope, (for looks), and with the standard 'Tube' BASE, that just plugs right in to replace the original tube!!  Of course there will be the arguments about purity/quality of sound, (for true valves), but these just plug right in to the original socket, as a replacement!
"Bones of contention" expected... Need a light globe inside, to look like a Filament!!   

[frozenfrogz]

A lot of places are now developing Solid State 'Tubes', although with no need for a vacuum inside.

Please define "a lot of places" and "now".

A several years ago some of those solid state 12AX7 / ECC83 retrofits have been on the market, AMT being one of the more prominent manufacturers.
https://amt-sales.com/other/tubes/amt-12ax7-warm-stone-tube/

However, in the past couple of years (3-5?) I was not able to track down anything on the market.
I would have been interested in buying a couple of these to knock down the current consumption of the +15VDC rails in several Ampeg SVT 7 pro amplifiers (pretty buggy designed). These are solid state Class D amplifiers with a single 12AX7 in the preamp stage. Getting rid of the heater current by replacing the valve with one of those solid state retrofits would have saved me a lot of trouble.

[Gyro]

Look up 'Fetrons', they were manufactured over 50 years ago! 

[Cyberdragon]

I hate these things, t throw em away if I see em in anything.

Get your damn trannies outta my shit.

[TimFox]

I remember when the Fetrons first came out.  One was a cascode device to replace 6AK5/5654 pentodes, which were extremely common in military RF devices.

[wraper]

Solid state replacement for tubes is ridiculous. You get the worst of two worlds. Not to say operation voltages are very sub-optimal for semiconductor amplifiers. You'd be far better with conventional semiconductor amplifier and fake tubes with fake LED filament for aesthetics.

[T3sl4co1l]

What's suboptimal about it?  Transistors amplify hundreds of volts just fine.

The main difficulty is, commercial devices aren't usually dimensioned to cater to such applications.  There aren't many 600V 100mA 10pF 20W MOSFETs, for example.

You are quite correct, it is easier to re-engineer the application, than design and order custom transistors with such ratings, when a suitable match is unavailable.

Tim

[wraper]

There aren't many 600V 100mA 10pF 20W MOSFETs, for example.

Another issue is how are you going to dissipate that power in tube package. Semiconductor operation temperature is much lower compared to tubes.

[6h8c]

Personally, I am against such substitutes. It's like choosing a cheap wine instead of Château Margaux from 1787

[james_s]

Some tubes such as power rectifiers are easily replaced with solid state, others are much harder. I recall there having been several attempts at making solid state tube replacements but only a few types had any real success. While they perform similar functions, the characteristics of tubes and transistors are just too different in many ways to make a direct substitution work.

I think it's largely kind of pointless anyway though. I mean if you want solid state gear just buy solid state gear, it's cheaper anyway.

[bob91343]

I have one of those fetrons meant to replace a 12AX7 if I remember correctly.  It is all metal outside and smaller than a tube, with no intent to fool anyone.  I suppose it works, never tried it.

[John B]

What's the market for them? Due to the packaging of them, it looks like it's supposed to have aesthetic appeal along with function, so is it aimed at the audio market? If so, that market would be the most likely to keep valves for the reason that they are valves, myself included.

If it was a retrofit to get an old piece of test equipment working, it could be done with a PCB with pins out the bottom or right angle to plug into the existing socket.

[Red Squirrel]

This could be a new trend in audiofoolery.  "Built with solid state vacuum enclosed audio grade transistors".  Essentially a transistor inside a vacuum tube with an actual vacuum.  The vacuum could somehow be said to affect the performance of the transistor by providing it a consistent atmospheric environment, or some wizbang theory like that. 

[Cyberdragon]

Some tubes such as power rectifiers are easily replaced with solid state, others are much harder. I recall there having been several attempts at making solid state tube replacements but only a few types had any real success. While they perform similar functions, the characteristics of tubes and transistors are just too different in many ways to make a direct substitution work.

I think it's largely kind of pointless anyway though. I mean if you want solid state gear just buy solid state gear, it's cheaper anyway.

The original FETrons weren't meant to fool anyone. But these fake tubes with the terribly painted on "getter" just are just for hipster audiophile wannabes (or potentially audiophools as mentioned). These also seem a lot more dangerous. With tubes if something goes wrong it gets hot and eventually burns out, with this crap is seems like one problem and BANG! , total carnage, goodbye to itself and any transformers if the FETS short due to improper bias or internal failure.

[GlennSprigg]

Personally, I am against such substitutes. It's like choosing a cheap wine instead of Château Margaux from 1787

'Wine' like most things in life is very SUBJECTIVE...   
I personally am NOT a fan of 'vintage' French/Italian wines. And I'm not talking about the taste of Toe-Nail clippings and uncontrolled Toe-Jam Fungai in their home-stomped 'vinegar'/bowel-clensers!!   
I know such 'tubes' are not for everyone, especially for serious 'restorers', but when someone wants to just 'plug-in' a replacement without historical genuine parts to make something work, then the alternatives are there.
MY 'reds' are full-bodied, dark, black-currant flavored, with no sharpness...  You can drink your own poison 

[peter-h]

I used to design with valves. EF80, ECC83, EL84, KT66, KT88, even the big 807 for pirate radio transmitters

A valve is basically a depletion mode N channel mosfet. Like the mosfets we have today but if Vgs=0 it is fully conducting, so the gate needs to go negative to get into the controllable region.

Hence valve circuits, to avoid a negative rail, have a resistor in series with the cathode, which lifts the cathode up by some 10-20V, so if the grid is near ground you have in effect a negative Vgs.

The only advantage of valves is that they were electrically very robust, and short of mechanical destruction they would be very hard to damage. This was good for rudimentary EMP protection

Valve amps are crap. It is purely a fashion thing. Many years ago, QUAD did a blind test of their 1950s valve amp and the then state of the art 405 amp. The audience was a load of hifi press VIPs. Nobody could tell the difference, statistically, between the two amps. The THD was a few % versus 0.01% or so...

[T3sl4co1l]

The audience was a load of hifi press VIPs. Nobody could tell the difference, statistically, between the two amps. The THD was a few % versus 0.01% or so...

And double-blind tests have been banned in hi-fi circles ever since.*   That tells you, basically all you need to know.

*I mean, I don't know that this story is true and the origin of that aversion, but it's the general idea in any case.

Tim

[engrguy42]

Anyone notice how discussions of analog stuff like scopes and tubes invariably end up with justifications like "it's like a fine wine" or "it's like driving a Bentley or a Mercedes" or  dissing those who buy "cheap plastic toys from China"?

Please, tell me there's more to it than that 

Look, if you like it just cuz you like it then admit it. No need to search for irrelevant and meaningless justifications to make it look more honorable.   

Reminds me of the PC techies who pee in their pants when a "faster" GPU with more fans and shiny lights comes out. Even if it's only 10% faster, with software that hasn't been developed yet. "Ooooo, more POWER !!!"   

[Tomorokoshi]

I don't need solid-state tube replacements. I tracked down the problem 2D21 just fine. What I really need is a schematic for the thing. Otherwise obscuriorata is difficult to fix.

[frozenfrogz]

Valve amps are crap. It is purely a fashion thing.

I do not fully agree.

For hifi stuff, I do not see much benefit in tube technology either and there is a sh*tload of voodoo devices with tubes in it, that do not actually give any benefits aside from looks and marketing blerb. However, I really like playing tube amplifiers on electric bass and electric guitar.
Yes, there are some digital modeling amps that can pretty much reproduce what the original tube amplifier sounds and feels like. However, these are expensive AF and just do not "click" with me. It is a bit like using the screwdriver on a multi-tool. It gets the job done, but a dedicated screwdriver with a nice wooden handle makes the job more fun.
There is nothing more satisfying than playing through my Mesa Bass 400+ or Peavey 3120.

[peter-h]

This is old stuff but valve circuits generate lots of even harmonic distortion which sounds less harsh than the mostly odd harmonic distortion from badly designed transistor stuff.

But anything that valves do one can do with transistors, fets, software, etc

[Cyberdragon]

But anything that valves do one can do with transistors, fets, software, etc

Except survive an EMP.

[retrolefty]

I don't need solid-state tube replacements. I tracked down the problem 2D21 just fine. What I really need is a schematic for the thing. Otherwise obscuriorata is difficult to fix.

 Boy the 2D21 brings back memories in the Air Force 66'-70'. They had a handful of them in the off-line KL-7
off-line cipher machine that were used to step the rotors.  https://en.wikipedia.org/wiki/KL-7

[Tomorokoshi]

I don't need solid-state tube replacements. I tracked down the problem 2D21 just fine. What I really need is a schematic for the thing. Otherwise obscuriorata is difficult to fix.

 Boy the 2D21 brings back memories in the Air Force 66'-70'. They had a handful of them in the off-line KL-7
off-line cipher machine that were used to step the rotors.  https://en.wikipedia.org/wiki/KL-7

The failed 2D21 was in the reset circuit of a counter I'm working on. The plate shorted to the heater, so it took down the +100V supply every time it triggered. It glows a nice purple from the xenon fill when that happens. I borrowed one from the HP 405CR, where it runs the autoranging stepper, so now I need to get a couple replacements. And to think I replaced a Nixie in it only a week ago, and now I'm borrowing parts out of it already.

[james_s]

Anyone notice how discussions of analog stuff like scopes and tubes invariably end up with justifications like "it's like a fine wine" or "it's like driving a Bentley or a Mercedes" or  dissing those who buy "cheap plastic toys from China"?

Please, tell me there's more to it than that 

Look, if you like it just cuz you like it then admit it. No need to search for irrelevant and meaningless justifications to make it look more honorable.   

Reminds me of the PC techies who pee in their pants when a "faster" GPU with more fans and shiny lights comes out. Even if it's only 10% faster, with software that hasn't been developed yet. "Ooooo, more POWER !!!"

This just sounds to me like someone who either can't afford nice things or who has never bothered to try complaining about others who do see value in it.

Have you ever driven a high end luxury car? Have you ever had good wine or an expensive steak? Have you ever used top quality tools? It has nothing to do with honor, some of us just enjoy nice stuff and I don't see what the issue is with that. Is there nothing in this world that you are enthusiastic enough about to dig into the finer nuances? Have you really never been tempted to spend more to get that extra 5%? Do you see no value in quality, fit & finish and attention to detail? Do you not appreciate the engineering and craftsmanship that goes into it? Or are you one of the masses of people who always shop purely by price and buy the cheapest stuff you can find in all categories while pretending it's as good as anything else around?

I don't mindlessly "diss" people who buy cheap toys from China. I mean I also buy cheap toys from China, a lot of cheap crap is completely usable within its limitations. I do look down upon those who mindlessly sneer at anyone who can see the value in better quality equipment though.

[engrguy42]

james_s, before you get offended, I think you're missing my point.

I certainly get that people think the old equipment is well engineered and high quality. In many cases I tend to agree. But folks here seem to be unable to comprehend how others might value things differently and have different priorities.

For example, I'm not a car guy. Yeah, I see how some cars are high quality and well engineered, but for the most part I don't give a rip about a Bentley or Mercedes. And while the old Tektronix analog scopes I used years ago are high quality, I don't care. I'm unwilling to invest money in them for a number of reasons. That doesn't mean I don't respect quality, it just means I'm not interested in investing in stuff solely because it is perceived as "high quality" or "well engineered". To me there are far more important criteria for judging stuff that I'm going to use and rely on. 

I'm an engineer, and if I need to use something on a practical and regular basis like a car and a scope I tend to value cost vs. benefit, not that it's old stuff that was well engineered. I value stuff that will last and be up to date and has the functionality I need.

Nor do I value fine wines. I don't like wine. So sue me. Instead I used to spend crap-tons of money going around the world doing scuba diving. Different people have different values. Would I ever recommend that everyone needs to spend all their money going around the world scuba diving, and search for a bunch of irrelevant reasons to justify my recommendations? Hell no. It's a dumb idea, and a waste of money. I freely admit it. And if you told me, "dude, you freakin' wasted tens of thousands of $$ with nothing to show for it", I'd be the first to agree.   

Now if others do value the old analog electronics stuff because it was well engineered then that's fine. I just wish people would be honest and say "yeah, basically I like it cause I like old stuff. And honestly, I don't think it's appropriate to recommend it to newbies (or anyone else) because, even though I like it and value it, it's probably not the best choice for someone starting out, for a number of reasons. Nor is it appropriate to look down upon those who have different values and priorities".

Now if someone actually believes that it's a good idea to recommend those old analog devices, then that's fine. As long as we're being honest and considering others' needs, not just our own biases.

Instead, as in most tech discussions all over the universe, it comes down to "I like it, therefore everyone should value the same thing and like the same thing", and people get upset when others disagree.

 

 

[sam[PS]]

vs 

valve circuits generate lots of even harmonic distortion

Please provide an actual frequency analyser plot to back up that, i'm very curious about is as all those i seen don't actually show that.

even harmonic distortion which sounds less harsh than the mostly odd harmonic

Please provide evidence, of course that's very subjective but still some protocole exist to get data on subjective things.

mostly odd harmonic distortion from badly designed transistor stuff.

Ha ok now i see so well designed tube circuits tend to sound better than bad designed transistor circuits. Well let's take the words "transistor" and "tube" out of there and that still stand true. Invert them and that still stand true. So yeah that's a good news for competent EE designer, there is still work for us.

And yeah that odd harmonic vs even harmonic thing is an argument that's been repeated a lot over the years. You ear/read that all the time whenever the subject of tube is put on the table. But actual measure are not consistent to it so...

Odd vs even harmonic is mostly a matter of topology i.e. single ended vs push pull, that's just basic mathematics (taylor series anyone ? ).
If you build a simple single stage triode common cathode voltage amplifier and a similar Jfet common source or a bjt common collector voltage amplifier, the three with the same voltage gain (under load please) and you just plot the harmonic content at the output using a frequency analyser  (the fft function of any decent digital scope will do just fine). You will see difference in the harmonics generated by those three circuit but those are most of the time nowhere near the statement you make. From the measure i seen and some i made triode tends to generate more harmonics both odd and even than the solid state counterparts but their harmonic spread is very focused on low order harmonic while solid state tends to generate more high order harmonic. Now with a penthode i got about the same spread as the Jfet, just more of it. I'd have to redo this experiment and document it one day, probably won't stop the myth to spread, actually it have been done several time in electronic magazines and the myth is still alive. Now it's an EE forum here not an audio forum, so please behave as an engineer and before spreading things get some measure done. 

Don't get me wrong i love tube. I play electric guitar and playing thru my all tube head give me thrill. And one of my curent electronic project is recreating original Beatles's era abbey road REDD .47 all tube mic preamps. But that's about mojo not EE !!!! I do believe mojo is something of importance in music, musician do play slightly better when they feel the look of the instrument they have in hand is cool. But that has nothing to do with the quality of the instrument. Same goes for tube vs solide state. 

Now the OP's subject is interesting could we please come back to it, and please talk a little more about EE and a little less propagating myths.

[John B]

I see nothing wrong with preferring tubes in an application where particular shaping or distortion of the waveform is the goal, ie a bass/guitar amplifier.

[Circlotron]

The best thing about valves is how they made you feel when you were a little kid, peering in the back of a running radio or tv, wondering just how it worked, smelling the warm transformers and dust. Now we're adults and that magic feeling has slipped through our fingers and we just want to relive it again. It's not technology, it's psychology.

[peter-h]

I think the last two posts above are spot on

[engrguy42]

The best thing about valves is how they made you feel when you were a little kid, peering in the back of a running radio or tv, wondering just how it worked, smelling the warm transformers and dust. Now we're adults and that magic feeling has slipped through our fingers and we just want to relive it again. It's not technology, it's psychology.

Perfectly legitimate. No question.

As long as everyone realizes and accepts that "how they made you feel" refers to how they made YOU feel, not the rest of the world.

[GlennSprigg]

(O.P. here).  Wow... Everything people are saying has merit/truth.
It gets down to 'young-un's' VS 'Oldies' here I think.  I didn't want to get into the 'finness' of the 'Sound'. As some people have touched on, some of us 'oldies' just love the LOOK & feel of old valve/tube equipment. NOT just for Amps, (with audio considerations) but even the likes of old Signal Generators, or Frequency Counters etc etc.  I don't care how long it takes to 'Warm Up', I just like the historical oldness of the construction, and the warm glow of the filaments, and the virtual 'artistic' beauty of the construction of some tubes! It excites us!!  And I know some tubes have limitations.

For instance... some people may not have known/grasp why we have/had 'Tetrodes' instead of just 'Triodes', especially for higher frequencies?  A 'Transistor', being so internally small/compact with it's P/N/P etc construction, doesn't have the SAME (keeping it simple here!) Reactances between the relatively 'large' mechanical design/size/spacing plates & components within a 'Tube'.  At higher frequencies, (in a typical 'Tube'), there is a now CONSIDERABLE amount of CAPACITANCE between the Grid & the Anode, to VASTLY effect the circuitry!!  The EXTRA Grid, (Screen Grid), is designed to cancel out, or at least greatly minimize this inherent internal capacitance...  (Typically held at about 70% of Anode voltage). MY POINT here, is to highlight that a lot of this 'WIZARDRY' is due to the PHYSICAL problems associated with some Vacuum Tubes. HOWEVER, we love to see the GLOW, as it brings us many memories of what once was!!   

[bobdring]

It is interesting that here we are seeing the valve transistor debate continue.
Being of the older generation I too remember valves. Then again I am firmly into solid state now.
Let me explain my current quandary:-

I recently acquired an elderly Leader LSG11 RF signal generator. It’s valve based.
I only got it because I wanted one in my youth and couldn’t afford it.
There is an article available about converting this SG to solid state and it then runs on a ht of 9V. The conversion needs other component changes.

I have three choices

1. Find 2 new valves and leave it original.
2. Convert it to solidstate as per the article and so make it not collectable
3. Come up with a plug in solidstate conversion that works at the original ht of around 100v.

I’m leaning towards #3 if I can dream up a circuit. I could then put valves in a bag inside the case  to allow for the future return to valve operation.

Any ideas?

Bob

[wraper]

3. Come up with a plug in solidstate conversion that works at the original ht of around 100v.

I wonder why would you bother with that nonsense which would be a piss poor hack and not original. I googled a bit and replacement tubes are easily available. And even when they are not, usually you can use a socket converter and use a different tube.

[vk6zgo]

It is interesting that here we are seeing the valve transistor debate continue.
Being of the older generation I too remember valves. Then again I am firmly into solid state now.
Let me explain my current quandary:-

I recently acquired an elderly Leader LSG11 RF signal generator. It’s valve based.
I only got it because I wanted one in my youth and couldn’t afford it.
There is an article available about converting this SG to solid state and it then runs on a ht of 9V. The conversion needs other component changes.

I have three choices

1. Find 2 new valves and leave it original.
2. Convert it to solidstate as per the article and so make it not collectable
3. Come up with a plug in solidstate conversion that works at the original ht of around 100v.

I’m leaning towards #3 if I can dream up a circuit. I could then put valves in a bag inside the case  to allow for the future return to valve operation.

Any ideas?

Bob

I also have a Leader LSG11,which I bought at a Hamfest for no other reason than that it was dirt cheap.

I've had a lot of use of it, but it is now awaiting recapping & ditching the selenium rectifier.
The Mains wiring is a bit "iffy", so I am thinking about fairly radically revamping that so that there is a power switch on the back, along with a IEC socket with built in fuse.

I think I might use the existing switch pot to turn the HT on & off, but that is probably too much of a "nicety" for an old "roughie".
Or I could just ditch it & buy a higher spec but still old sig gen.

The tube complement of the Leader is another thing----I've probably got a 12BH7 in my odd valves, but a I doubt there is a 6AR5 there.

I did "solid state" a dipmeter, but that was to eliminate the power cord limitation on where I could use it.

[floobydust]

Leader LSG-11 converted to solid state back in 1970. The wheel must be reinvented lol. It does run off a 9V battery now instead of mains.
If you left it with tubes but go from selenium to silicon rectifier, I end up adding a zener like 150V or 200V 5W to keep B+ from going too high. Or resize the 3kΩ resistor.

[b_force]

I don't understand the whole negative and snarky vibe in this topic?

After a week of working with all kinds of micro's, DSP and multi-layer boards, I sometimes like to dive into some tube circuits, old tube radios and builds as well.
Why?

Because it's simple, straightforward and you can basically draw out an entire circuit on the back of an envelope.
You can also assemble and work on it on the fly basically, without having to stare at a monitor screen for hours.
The mechanical structures just looks a lot better than an unknown blob of something on some kind of multi layer PCB.

Is it "better", more efficient etc? No of course not!
It's just pure interest and fascination of technology and history in general.
For the same reason I have also converted solid state circuits to tube sockets, just simply to match the look-and-feel of the whole device.

Not everyone who works with tubes/valves is a total audiophool lunatic.
And still, what if someone is?

The very vast majority of engineers have a oscilloscope and DMM/benchmeter that they purely bought for kicks, specs and looks.
Most people don't even use 1/100th of the capabilities or barely know of all its functions.
In fact, I know and have seen many people who don't even use them at all!

Other people buy a fancy car, sofa or motor bike for no particular reason.

Same thing, just different.

[wraper]

I don't understand the whole negative and snarky vibe in this topic?

It's about making a stupid drop in solid state replacement for tubes rather than tubes as such.

[floobydust]

It was already tried with Fetrons, look at the claims of millions of $ to be made in telecom swapouts.
Teledyne Fetron (late 1960's) but they flopped due to price, crazy expensive. I thought ~12x the price of a tube. It's too bad, the ENIAC surely could have used some There were some HP400 and Tektronix 500 CA series upgrade kits too.
It may have been the high labour costs in making them, or the price point was too greedy I'm not sure.
Example inside they used 2N4881 HV JFET's 300V TO-5 I_DSS 0.4-2mA along with a small 2N3823 for the input. JFETs from Teledyne (Amelco databook).
Today, you can find HV depletion-mode MOSFET's by IXYS to 1,700V. If that's your thing.
In winter time I get 100% efficiency with tube gear heating my house 

[EPAIII]

The idea has been around for quite some time. It probably started with rectifiers.

The big problem is they don't heat the room in the winter like real tubes do. Or in the summer for that matter.