Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
Tube Rolling:-
Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? and Hey Mr. Ian, you rock Sir |
#2
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
Sorry for the cross/double post. I am new to newsservers!
|
#3
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
"TheOctavist" wrote in message
4.90 Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objective evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. I'm sure the manufacturer's know, but don't want to talk. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. I know of no DBTn that was ever done to study that question. And would be the right way to do it. |
#4
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
On Apr 16, 5:14*am, TheOctavist wrote:
Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? and Hey Mr. Ian, you rock Sir If by 'objective evidence' you include measurements, you can generally say that performance differences can be measured with different tubes. As tube equipment is often designed with little or no feedback they are much more sensitive to individual tube parameters than ss equipment where the feedback makes sure that individual active device performance differences do not lead to measured or otherwise objective differences. jan didden editor/publisher Linear Audio |
#5
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
janneman wrote:
On Apr 16, 5:14*am, TheOctavist wrote: Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? and Hey Mr. Ian, you rock Sir If by 'objective evidence' you include measurements, you can generally say that performance differences can be measured with different tubes. As tube equipment is often designed with little or no feedback they are much more sensitive to individual tube parameters than ss equipment where the feedback makes sure that individual active device performance differences do not lead to measured or otherwise objective differences. Triodes already include quite heavy internal feedback because the anode potential affects the potential gradient between the cathode and grid. The screening grid of the tetrode and pentode removes that feedback to allow much higher voltage gain*. Because of this, triode circuits give reasonably stable gain without external feedback, whereas pentode circuits are more dependent on individual valve characteristics. A prudent audio designer always arranges feedback around a circuit containing a pentode (things are not as straightforward at R.F.). *The original purpose of the screen grid was to reduce the anode-grid capacitance (and the Miller effect) which restricted the H.F. amplifiaction of triodes. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk |
#6
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
On Apr 17, 9:50*am, (Adrian
Tuddenham) wrote: janneman wrote: On Apr 16, 5:14*am, TheOctavist wrote: Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? and Hey Mr. Ian, you rock Sir If by 'objective evidence' you include measurements, you can generally say that performance differences can be measured with different tubes. As tube equipment is often designed with little or no feedback they are much more sensitive to individual tube parameters than ss equipment where the feedback makes sure that individual active device performance differences do not lead to measured or otherwise objective differences. Triodes already include quite heavy internal feedback because the anode potential affects the potential gradient between the cathode and grid. The screening grid of the tetrode and pentode removes that feedback to allow much higher voltage gain*. Because of this, triode circuits *give reasonably stable gain without external feedback, whereas pentode circuits are more dependent on individual valve characteristics. *A prudent audio designer always arranges feedback around a circuit containing a pentode (things are not as straightforward at R.F.). *The original purpose of the screen grid was to reduce the anode-grid capacitance (and the Miller effect) which restricted the H.F. amplifiaction of triodes. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply)www.poppyrecords.co.uk- Hide quoted text - - Show quoted text - Ahh yes, good points indeed. But wouldn't you agree that in tube equipment, even in pentode/tetrode circuits, feedback factors are generally much lower than in ss? I mean, the fact that over the limited life time of tubes you can measure (some say hear) changes does point to equipment parameter variation with device parameters. And of course tube rolling would be senseless if device parameters were hidden by the circuitry! jan didden |
#7
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
janneman wrote:
On Apr 17, 9:50*am, (Adrian Tuddenham) wrote: janneman wrote: On Apr 16, 5:14*am, TheOctavist wrote: Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? and Hey Mr. Ian, you rock Sir If by 'objective evidence' you include measurements, you can generally say that performance differences can be measured with different tubes. As tube equipment is often designed with little or no feedback they are much more sensitive to individual tube parameters than ss equipment where the feedback makes sure that individual active device performance differences do not lead to measured or otherwise objective differences. Triodes already include quite heavy internal feedback because the anode potential affects the potential gradient between the cathode and grid. The screening grid of the tetrode and pentode removes that feedback to allow much higher voltage gain*. Because of this, triode circuits *give reasonably stable gain without external feedback, whereas pentode circuits are more dependent on individual valve characteristics. *A prudent audio designer always arranges feedback around a circuit containing a pentode (things are not as straightforward at R.F.). *The original purpose of the screen grid was to reduce the anode-grid capacitance (and the Miller effect) which restricted the H.F. amplification of triodes. Ahh yes, good points indeed. But wouldn't you agree that in tube equipment, even in pentode/tetrode circuits, feedback factors are generally much lower than in ss? Yes, larger numbers are used when describing external feedback in SS circuits, but they don't always accurately reflect what is really going on. Perhaps less external feedback is needed in a valve circuit because it already has enough internal feedback - or perhaps the valve circuit contains a transformer with phase shifts which limit the amount of feedback which could be safely applied around that stage - or perhaps the transistor circuit generates such a high distortion level that it only becomes acceptable with masses of feedback. In most cases the designer knows the answer (if he is doing his job properly), but the salesman is never going to let you find out. You have to be very careful how you define the level of feedback. Consider an amplifier which, without feedback, has 10 dB more gain at 1 Kc/s than it does at 100 c/s and 10 Kc/s (very poor) and you decide to flatten the frequency response by applying12 dB of feedback. The feedback at 1Kc/s would indeed be 12db, but at 100 c/s and 10 Kc/s it would only be 2 dB. Take another case of a Class-B transistor output stage where the gain varies according to the current in each of the devices. How much feedback are you really using when the loop gain, bandwidth and slew-rate all vary wildly throughout each cycle of the audio waveform? In both these examples, the true feedback is greatest under the maximum gain condition, which is not very helpful for counteracting the shortcomings at the low-gain ends of the performance (which is what feedback is often intended to do). Furthermore, you need to consider how much feedback already exists inside the device or its immediate circuitry, before you apply external feedback. You would find it difficult indeed to design a worthwhile one-transistor audio amplifier without any feedback at all, the distortion would be horrible at anything other than the smallest signal levels. In contrast, a single pentode without feedback gives quite passable results for domestic equipment - and single triodes were used in good quality professional equipment without external feedback for many years. One big advantage of external feedback is that it puts the overall performance of the circuit under the designer's control. He is not tied to a certain characteristic determined by the valve manufacturers' grid wire geometry. Worse still, the tolerances on semiconductors are so wide (and so temperature dependent) that it would be impossible to stay within any kind of worthwhile specification without feedback in SS circuits. I mean, the fact that over the limited life time of tubes you can measure (some say hear) changes does point to equipment parameter variation with device parameters. If the circuit is well designed, you should not hear any change until the valves degenerate to the point where they fall well outside their design characteristics. Even a small amount of feedback will take care of that. For triodes, which are used without external feedback, the grid geometry determines the amount of internal feedback (until the end of life) and that is unlikely to have any significant wear-out mechanism. You may well hear changes if pentodes are used without feedback, as in some domestic tape recorders and cheap P.A. amplifiers, but that is because the design was driven by the need for the minimum number of valves, not for a good specification and reliable long-term operation. And of course tube rolling would be senseless if device parameters were hidden by the circuitry! I'm not sure what you mean by 'tube rolling', but if you mean using the uncorrected large-signal characteristics of a valve to create distortion effects, then I agree with you. In that case you would definitely expect to hear changes as the device aged (more-so for a pentode than a triode). However, that is the exact opposite of what a good valve amplifier designer strives to achieve. Valves can be used for stable high quality audio amplifiers, they can also be used for effects units. Some poorly-designed amplifiers have unintentional effects units built into them by mistake and a few specialist musical instrument amplifiers have them by design. None of this says anything about the valve itself (as compared with the transistor), it is just a matter of how it is used. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk |
#8
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
"janneman" wrote in message
On Apr 17, 9:50 am, (Adrian Tuddenham) wrote: janneman wrote: On Apr 16, 5:14 am, TheOctavist wrote: Tube Rolling:- Valves have certain specs, which all manufacturers of, say, an ECC83 adhere to in terms of gain, bias sensitivity, mutual conductance etc. All manufacturers have production spreads, so that a valve may have low gain, another of the same type higher gain, but still within the acceptable spread. Is there any objectove evidence that a say, Mullard, ECC83 is any different in spreads and performance than any other manufacturer's. Is there any objective evidence that a say, Mullard, valve will sound any different to another manufacturer's valve. Is there any objective evidence that valve circuits are so sensitive to changing valves unless it's clear that it's due to the valves being at opposite ends of their production spreads. Or is it yet another audiophile myth? If by 'objective evidence' you include measurements, you can generally say that performance differences can be measured with different tubes. As tube equipment is often designed with little or no feedback they are much more sensitive to individual tube parameters than ss equipment where the feedback makes sure that individual active device performance differences do not lead to measured or otherwise objective differences. That tubed equipment has less loop feedback and often has less local feedback than SS gear is a matter of scientific fact. I'm old enough that my formal education started with tubes and SS was sort of an add-on. The first thing we were told was that the transfer characteristics of transistors were much like pentodes, and that transistors had far less built in resistance and local feedback than tubes. Triodes already include quite heavy internal feedback because the anode potential affects the potential gradient between the cathode and grid. Right and quality tubed audio gear used lots of triodes. Furthermore, the classic tubed preamp used cascaded triodes with loop feedback, either for RIAA equalization or tone controls. The screening grid of the tetrode and pentode removes that feedback to allow much higher voltage gain*. Tetrodes and pentodes usually ended up in power amplifiers where they were typically enclosed in feedback loops. Because of this, triode circuits give reasonably stable gain without external feedback, Nevertheless quality equipment often put its triodes inside feedback loops. whereas pentode circuits are more dependent on individual valve characteristics. A prudent audio designer always arranges feedback around a circuit containing a pentode (things are not as straightforward at R.F.). RF amplfiers in tuners often had "neutralization capacitors" hooked from the plate to the grid. This is inverse feedback. *The original purpose of the screen grid was to reduce the anode-grid capacitance (and the Miller effect) which restricted the H.F. amplifiaction of triodes. Agreed. Ahh yes, good points indeed. But wouldn't you agree that in tube equipment, even in pentode/tetrode circuits, feedback factors are generally much lower than in ss? This is true, but open loop gain and open loop nonlinearity is often greater in SS circuits. I mean, the fact that over the limited life time of tubes you can measure (some say hear) changes does point to equipment parameter variation with device parameters. Agreed. And of course tube rolling would be senseless if device parameters were hidden by the circuitry! The renewed interest in tubed circuits with no loop feedback seems to be pandering to tube rollers. |
#9
Posted to rec.audio.tech
|
|||
|
|||
Valve Questions
"Arny Krueger" wrote in message
That tubed equipment has less loop feedback and often has less local feedback than SS gear is a matter of scientific fact. Correction: That tubed equipment has less loop feedback and often has *more* local feedback than SS gear is a matter of scientific fact. Reality is that SS technology has made it economical to build audio gear that is incredibly linear by the standards of the days of vacuum tubes. It didn't start out that way, as the early SS gear had similar amounts of distortion as the vacuum tubed gear it replaced. But tubes were near the end of their development cycle and SS was near its beginnings at that point. These days an audio op amp that doesn't get under 0.001% THD @ 1 KHz gain = 10 probably won't sell at all. Too crude. I think that the newest chips are 10 or 100x better. I don't know how anybody would build a vacuum tube gain of 10 stage with even 0.001% THD. If memory serves, even getting much under 0.03% @ 1v from a tubed preamp was rare. Some old timers like to pretend that this kind of performance is some kind of a trick or a lie. It is achieved the old fashioned way - build something as linear as you can, and then improve it with feedback. If there has been a shift, the shift is from less local feedback to more loop feedback. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Reason 3.0 Install Questions, questions... | Pro Audio | |||
Jolida 502a ----Chassis is missing C7.....Questions questions..... | Vacuum Tubes | |||
Not valve again :-) its | Vacuum Tubes | |||
Why Valve? | High End Audio | |||
valve questions | Tech |