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Do tubes do anything well in circuits?

Brab

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Around here, my impression is that tubes are considered distortion generators and little else. In my time with tube amplifiers I remember reading that there were certain things that tubes do better than solid state components. I know nothing about electronics but am interested in whether there is any truth to that, and if so, could whatever that is be incorporated in circuit design.
 

MakeMineVinyl

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Around here, my impression is that tubes are considered distortion generators and little else. In my time with tube amplifiers I remember reading that there were certain things that tubes do better than solid state components. I know nothing about electronics but am interested in whether there is any truth to that, and if so, could whatever that is be incorporated in circuit design.
Tubes are not 'distortion generators' unless the circuitry is poorly designed or (common these days) deliberately designed to add distortion because of marketing expectations. In fact, tubes themselves can be more linear devices than transistors. They just don't have the gobs of gain of transistors and therefore don't have as much gain available for negative feedback to get distortion down to 0.0000x% levels. Still, distortion in well designed circuits can be at inaudible levels, and more importantly, tend to be low order harmonics which makes them even more inaudible.
 
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sergeauckland

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They'll stand a nuclear EM pulse much better than most SS device, so after WW3, you'll be able to use your Dynaco amp when all the others are burnt out.

Vacuum devices are still of use in very high power transmitters, and in generating microwaves, but for home HiFi, there's nothing I can think of where vacuum devices are better, except possibly looking great.


S
 

NiagaraPete

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Tubes clip nicely.
 

0bs3rv3r

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In fact, tubes themselves can be more linear devices than transistors.

Yes. Consider a triode used as a preamp. Power supply is typically a couple of hundred volts. For small signals, you are using only millivolts on the (typically quite linear) characteristic curve, out of a hundred volts or more. The linearity within such a small region is excellent.
 

Jim Matthews

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Not all tubes are well behaved.
Not all well-behaved tubes are expensive.

The real advantage that contemporary amplification has (over *most* tube designs) is that the output devices don't require a transformer and the power supplies are at lower voltages.

Solid state devices based on the transistor are smaller, less expensive and don't use much power (compared to tubes).

Beware any tibe device where the tubes are used as buffer stages, and don't actively amplify the signal.
 

0bs3rv3r

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The real advantage that contemporary amplification has (over *most* tube designs) is that the output devices don't require a transformer

This is only true for tubes driving low impedance - i.o.w. output stages of power amps. Tubes in preamps and lots of other applications do not require transformers at the output.



Beware any tibe device where the tubes are used as buffer stages, and don't actively amplify the signal.
Yes, the buffer stage (typically a cathode follower) is very transparent and doesn't have a "tube sound" (contrary to what most say about tubes)
 
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Brab

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My one remaining tube component is an EAR 834P phono stage, which I think has a 12AX7 cathode follower.
 

JeffS7444

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DIY with tubes can be lots of fun and more forgiving of rookie mistakes. And where modern electronics are usually "No user serviceable parts inside", not only are there user-serviceable parts in a tube amp, it's a part of the tube experience. Amp and preamp circuits are usually pretty simple and a good way to learn about how these things work.
 

DVDdoug

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Around here, my impression is that tubes are considered distortion generators and little else. In my time with tube amplifiers I remember reading that there were certain things that tubes do better than solid state components. I know nothing about electronics but am interested in whether there is any truth to that, and if so, could whatever that is be incorporated in circuit design.
Tubes and transistors (including FETs and MOSFETs) are are all "similar" in that they allow you to control a large voltage and/or current with a much smaller voltage/current, In other words, it's an amplifier.

An analogy is the gas pedal in your car. The pedal controls fuel to the motor to control speed of your car. The muscles in you leg aren't moving the car.

Any of these things can give you good sound but the older technology is more expensive (especially if you want good sound) and tubes are much less energy efficient. An op-amp costs a couple of dollars (or less) and it can contain hundreds or of transistors.

Tubes are also less stable. As the tube ages the characteristics change. That can be designed-around (with negative-corrective feedback, etc.). But some tube designs are intentionally designed to sound different when you swap tubes and that's not a stable design. Transistor/MOSFETs also very from part-to-part so again feedback (etc,) is used to get predictable performance, but sold state parts don't "age".

Jim mentioned output transformers (for power amplifiers). Again that's a very expensive item if you want flat frequency response and low distortion, and the more power you need the bigger and more expensive it gets. Some preamps use input & output transformers but they can be built without them. The smaller transformers also aren't cheap but they are more affordable than a power-output transformer. (Low-power audio transformers can be reasonably priced if you don't need good sound quality, but it's still an added expense.)

Overall the cost-per-watt is MUCH lower with solid state. And there aren't a lot of high-power tube amps. It's easy to find 1000W (or more) solid state amps but I don't know if I've seen a 500W tube amp,
 

MakeMineVinyl

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Tube power amplifiers were / are usually used with more efficient speakers with milder impedance curves which makes up for the power deficit. My HF horns for instance are driven by a 2 1/2 watt amplifier, and the LF is driven by 40 watts.
 

0bs3rv3r

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Tube power amplifiers were / are usually used with more efficient speakers with milder impedance curves which makes up for the power deficit.

True, but the trend to "needing" high power was caused by the emergence of high power solid state amplifiers. This allowed manufacturers to make inefficient speakers in their experiments to try to "improve" the sound. Until this happened, most speakers were much more efficient. Sort of self fullfilling, and not really a limitation of tubes.
 

syn08

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Yes. Consider a triode used as a preamp. Power supply is typically a couple of hundred volts. For small signals, you are using only millivolts on the (typically quite linear) characteristic curve, out of a hundred volts or more. The linearity within such a small region is excellent.

Dead wrong, and then wrong again. The linearity (or lack thereof) can be estimated by analyzing the behaviour in a small vicinity around the bias point. The usual tool is a series, and a quick math analysis will show that the polynomial coefficients of the expansion are proportional to the nth derivative of the transfer function and NOT by the absolute value of the bias point.

In this sense, it could be argued that a triode is more “linear” that a bipolar transistor (since the IV of a triode is parabolic, while a bipolar transistor is exponential) but certainly not more “linear“ than a JFET, which is parabolic too. But certainly the fact that tubes can be fed with high voltages is totally irrelevant from a “linearity” perspective.
 

restorer-john

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They'll stand a nuclear EM pulse much better than most SS device, so after WW3, you'll be able to use your Dynaco amp when all the others are burnt out.

But you'll have to dig out your turntable to play anything, on your generator, because all the AM and FM radio stations will be down, your CD player will be toast and as for the streamer and PC- let's not go there. All the power station will be 'offline'. Interent? Forgeddaboudit... ;)
 
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escksu

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They'll stand a nuclear EM pulse much better than most SS device, so after WW3, you'll be able to use your Dynaco amp when all the others are burnt out.

Vacuum devices are still of use in very high power transmitters, and in generating microwaves, but for home HiFi, there's nothing I can think of where vacuum devices are better, except possibly looking great.


S

Yes, fully agreed. Vacuum tubes are extremely resilient. They are still very common in satellites today.

https://spectrum.ieee.org/the-quest-for-the-ultimate-vacuum-tube
 

restorer-john

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I remember reading that there were certain things that tubes do better than solid state components

Tubes (valves) definitely are better for heating in winter than solid state, unless you are a SS Class A aficionado.
 

Jim Matthews

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Thanks, everyone, for taking my naive question seriously. The replies are very informative.
If you're serious about the pursuit, we mean to help.
 
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