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Tubed Power Amplifiers. Are the disadvantages too great ?


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Had a thought yesterday about tubed power amps. I have many friends who will never consider a solid state power amplifier. I am not one of them. I certainly understand the fluidity and “beauty” of tube gear. Nevertheless, considering the great solid state amps out there, the question stands.

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Not sure what disadvantages are concerning you.  Yes, they use more power and generate heat.  Yes, you have to replace a valve VERY occasionally, but then there's fun in selecting different valves.  Yes, some speakers may not be suited for use with them, but then, with the right speakers, they sing better than with SS amps.

 

None of that puts me off in the slightest.

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Disadvantages?

Like being able to tune the sound to your liking to a high degree with just rolling some tubes? ( you don't need a tech for that or having to buy a whole new amp if you don't like the sound)

Or, like having the option to change the sound with different coupling caps? (Again, if you are a bit handy you can do that yourself. Not so easy in an ss amp)

Once you have a set of efficient tube friendly speakers there are only advantages.

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11 hours ago, Hibard said:

I certainly understand the fluidity and “beauty” of tube gear.

Most of us do.

12 hours ago, Hibard said:

Nevertheless, considering the great solid state amps out there, the question stands.

There indeed are (disadvantages) and I would ever consider tube amp for only certain kind of music. Like small combo of piano or guitar  and bass. Maybe vocal or soft piano trio.

 

And disadvantages are numerous.

Firstly - to my surprise - I have been told at a recent GTG, that when paired with very high efficiency speakers, tube amps hum. 

I did hear this on numerous occasions and always thought of this as either fault or due to interference induced into some non-shielded audiophile cables.

But apparently not so. 

My 100W/ch solid state EC amplification is dead silent when fully open and so is 40 years old Quad 45/405. Admittedly into much less efficient speakers.

 

Then, there is a fact of their high output impedance and hence unsuitability to be used in power amps. Even when transformers are used on the output, their control of bass driver is poor. 

 

Next disadvantage is their high cost.

Most of the time only simple single ended designs are built and in recent times I have seen only one balanced Sonic Frontiers pre-amp for sale here on SNA. I am sure that there are some very good balanced power amps too, but hardly any at a price lower than a car.

 

Durability is not great either. Not many survive in fully working order for decades without extensive renovations. That Quad 45/405 I mentioned above is 40 years old and started to hum after being left abandoned in a tin shed for 3 years. Replacement of two 47µF capacitors in the pre-amp (worth $1.50 in total) made it as good as new.

 

So despite their undeniable appeal there is a reason for valves' limited uptake.

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This seems to be a personal rather than a technical discussion--which is fine. There is only one compelling reason for my attraction to valve amps: they sound more like music to me. 

 

Unless you enter  the stratosphere of SS implementation. And not that all valve amps sound good. Or for every kind of music.

 

But even the amps of yesteryear like the Quad/Leak/Rogers/Dynaco sound very good to me, and as for the Shindo/Leben/Audio Note/Earle Weston/Supratek of today, then I just can't help smiling widely when I hear them!

 

Good thing I'm not an electrical engineer or I'd be worried about distortion and such...

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1 hour ago, rockeater said:

Firstly - to my surprise - I have been told at a recent GTG, that when paired with very high efficiency speakers, tube amps hum. 

I did hear this on numerous occasions and always thought of this as either fault or due to interference induced into some non-shielded audiophile cables.

But apparently not so. 

My 100W/ch solid state EC amplification is dead silent when fully open and so is 40 years old Quad 45/405. Admittedly into much less efficient speakers.

 

Yes, there's no reason valves should hum more than SS.  It just comes down to design.  Other noise, such as microphonics, can be more troublesome in valve design.

 

1 hour ago, rockeater said:

Then, there is a fact of their high output impedance and hence unsuitability to be used in power amps. Even when transformers are used on the output, their control of bass driver is poor. 

I currently bi-amp, and the bass channel is class D, for this very reason.

 

1 hour ago, rockeater said:

Most of the time only simple single ended designs are built

Not sure this is true.  I see lots of PP designs.  There ARE a lot of SE amps, but I think that's because some of us like the sound.

 

1 hour ago, rockeater said:

Durability is not great either. Not many survive in fully working order for decades without extensive renovations.

SS designs are just as bad.  Most SS designs contain MANY electrolytic caps and after a few decades, these need replacing, just like in valve amps.

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40 minutes ago, doogie44 said:

 

 

Good thing I'm not an electrical engineer or I'd be worried about distortion and such...

 

Don't worry.  Plenty of smart electrical engineers fully realise what's going on in hifi, and understand and accept why people like valve amps - and own valve amps themselves.   I know this is contrary to the ideas peddled by the science haters, but...

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14 hours ago, Hibard said:

Had a thought yesterday about tubed power amps. I have many friends who will never consider a solid state power amplifier. I am not one of them. I certainly understand the fluidity and “beauty” of tube gear. Nevertheless, considering the great solid state amps out there, the question stands.

The era of tubed amps created some of the very best circuit implementations , namely common grid and cascode stages. 

 

Solid State can also adopt the same implementations using transistors , however you need to research very well to find them.    https://www.passlabs.com/press/cascode-amp-design    There is I should warn often misuse of the word cascode , which gets tumbled to include cascade implementations. When reviewing schematics if you wish to take it that far - the upper transistor with cascode has its base of gate ( as a fet or mosfet ) at a low voltage potential which can include both negative and ground potentials.  Cascade is more the series joining of devices. 

 

Quad's triple stage in the 303 , and current dumping in later models, began again 1967 on-wards to interpret good implementations, related to the requirements of solid state. This was very much Peter Walker's ( Quad founder, often referred to as the Quadfather ) passion to achieve the best possible amplification. Peter was always striving for the lowest distortion against other amplifier manufacturers ( Leak Point One as example ) 

 

Douglas Self's examination of what is referred to as the blameless amplifier gives excellent review of each contributing stage that makes up a power amplifier. http://www.douglas-self.com/ampins/dipa/dipa.htm

 

Solid state amps exhibit better power delivery into low impedance loudspeakers <8, whereas tubed amplifiers do the opposite exhibit better power delivery into high impedance loudspeakers >8.   A tubed amp is a great choice if your loudspeaker has impedance above 8 ohms. 

Edited by stereo coffee
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@Hibard, you said you have many friends with valve amps. What do your ears tell you when you listen to their systems? Maybe you could mention the names and models of some of the amp and speaker combos you've listened to? 

The main disadvantage is a lot of commonly available speakers aren't designed with valve amps in mind. And a lot of speakers don't come with meaningful specs, let alone test results and graphs. And the same can be said for valve amps, especially in regards to the actual output impedance at the tap. That is also too seldom specced. Manley Labs are one of the few who provide those vital numbers up front.

But get the amp/speaker interface sorted, your music collection and ears should be well served.

I got hooked on valve amps a decade ago but gave ss another turn 5 years ago. Yeah, nah.

 

Edited by deanB
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1 hour ago, deanB said:

 

The main disadvantage is a lot of commonly available speakers aren't designed with valve amps in mind. And a lot of speakers don't come with meaningful specs, let alone test results and graphs.

I have never gone wrong just making sure they are the correct nominal impedance, and of suitable efficiency/sensitivity to make loud enough noise given the power of the valve amp and the size of your room.  Nearly all speakers give you impedance and efficiency - if they don't, then don't buy them :) 

 

For example, normally you would say an inefficient 83 db 2-way bookshelf speaker would be no good paired with a 2.5 watt triode amp - however, when used in an office with the speakers in a bookshelf about 1 meter away from the desk, even these speakers are plenty loud enough and sound great.

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9 hours ago, rockeater said:

 

 

And disadvantages are numerous.

Firstly - to my surprise - I have been told at a recent GTG, that when paired with very high efficiency speakers, tube amps hum. 

I did hear this on numerous occasions and always thought of this as either fault or due to interference induced into some non-shielded audiophile cables.

But apparently not so. 

 

Like I said at that particular GTG, the hum is mostly due to the 300B ac heater supply. For various reasons some builder shy away from dc supplies.

I use DC supply on my builds and I do not have any hum through my 99db speakers.

I have to get you to come and have a listen to my SET Rockeater.

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9 hours ago, rockeater said:

Firstly - to my surprise - I have been told at a recent GTG, that when paired with very high efficiency speakers, tube amps hum. 

In my experience, it's more of a hiss than a hum. At leas that's what I hear with my high efficiency speakers (~105dB).

 

But unless you have an edge case (like mine), it's unlikely that you'll hear anything of concern with a well designed tube amp

Edited by sir sanders zingmore
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15 minutes ago, Ihearmusic said:

Like I said at that particular GTG, the hum is mostly due to the 300B ac heater supply. For various reasons some builder shy away from dc supplies.

I use DC supply on my builds and I do not have any hum through my 99db speakers.

I have to get you to come and have a listen to my SET Rockeater.

 

Using a pot to balance the heater ac supply gets me there, but nothing is as quiet as DC, true.  In practice, you absolutely cannot hear any hum unless you stick your ear right into my speakers.

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3 hours ago, aussievintage said:

Nearly all speakers give you impedance and efficiency

I never said they didn't. I want more information than that. 

3 hours ago, aussievintage said:

f they don't, then don't buy them :)

Don't talk to me like I'm a peanut.

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14 minutes ago, deanB said:

I never said they didn't. I want more information than that. 

Don't talk to me like I'm a peanut.

Wow, sorry.  Never meant it that way at all.      Hence the smiley...

 

My point was that it isn't as hard as some say to get a valve amp working with a given speaker, even with little info.

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On 30/01/2020 at 6:41 PM, Hibard said:

Had a thought yesterday about tubed power amps. I have many friends who will never consider a solid state power amplifier. I am not one of them. I certainly understand the fluidity and “beauty” of tube gear. Nevertheless, considering the great solid state amps out there, the question stands.

Yep as other's have suggested many variables at play. Speakers, Music Preferences, Budget, Maintenance etc.

 

An option might be to consider a Hybrid Power Amp. I put my Hybrid Mono Blocks into one of my Set-ups recently, sound very nice. Personally I think the Thrax Hybrid Teres Mono blocks may be the best Power Amps I have experienced.

Edited by initforthemusic
Needed to put Hybrid after Thrax.
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  • 2 weeks later...

High voltage caps in a SET design can have difficulty with our wandering line voltages. I got sick of replacing caps (and fried resistors) in my Audio Aero monoblocs and bought a Furman voltage regulator to solve the problem of a design operating rather close to tolerance limits. No problems since.

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2 minutes ago, Super Mustud said:

High voltage caps in a SET design can have difficulty with our wandering line voltages. I got sick of replacing caps (and fried resistors) in my Audio Aero monoblocs and bought a Furman voltage regulator to solve the problem of a design operating rather close to tolerance limits. No problems since.

A very generalized statement. Properly rated components can handle wandering line voltages. Your amp may have another problem or it is just a bad design.?

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15 minutes ago, Ihearmusic said:

A very generalized statement. Properly rated components can handle wandering line voltages. Your amp may have another problem or it is just a bad design.?

 

Yeah, I have made many different SET and SE style amps and NEVER blown a cap.  It's poor design I'll bet

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