Tube amps have more than one tube?
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- KVRAF
- 16891 posts since 8 Mar, 2005 from Utrecht, Holland
Firstly there's more than one amplification stage: a preamp stage (raise guitar level to line level or hotter) and the power amp stage (raise to speaker levels).
But there are also designs in which two tubes are used for each stage: one for the negative half and one for the positive half of the signal. Or use two amp circuits in parallel to give more power...
Some amps also have tubes in the cirquit that deals with the power supply.
But there are also designs in which two tubes are used for each stage: one for the negative half and one for the positive half of the signal. Or use two amp circuits in parallel to give more power...
Some amps also have tubes in the cirquit that deals with the power supply.
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- KVRAF
- 16891 posts since 8 Mar, 2005 from Utrecht, Holland
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- KVRist
- 490 posts since 8 Mar, 2005 from Helsinki, Finland
My Echocord Super S65 tape echo (that also acts as a preamp) has a total of seven tubes inside 
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- KVRist
- 187 posts since 20 Jul, 2004
Tube-based gain stages can be a bit tricky to design, for example the input impedance of a stage will usually decrease if it's configured for large gain (this happens to transistors too btw, OP-amps otoh are much easier to work with). One solution to this might be to place a buffer stage before the first gain stage in order to get a high input impedance (which is generally desireable), this will of course add one tube per channel. Furthermore certain gain stage designs will require the use of several tubes (e.g. the push-pull output stages that BertKoor mentioned or darlington-style stages). Also, to get control over the amount of distortion in an amp designed to provide this effect, there might be a separate stage for this which might utilize yet another tube.
If you add up all these stages you might find 1 (input buffer) + 2 (darlington-style gain stage) + 1 (clipping stage) + 2 (push-pull output stage) for a total of of 6 tubes in the amp, although some tubes provide two separate channels in one package so the number of physical tubes found might be smaller.
Also, there are certain advantages to design rectifier bridges using tubes (the "standard" solution would use diodes instead, BertKoor mentioned this too since the rectifier would be part of the PSU), a tube based-rectifer would add another four tubes to the amp (I would guess that other parts of the PSU might utilize tubes instead of more modern components, but I'm not sure about this).
If you add up all these stages you might find 1 (input buffer) + 2 (darlington-style gain stage) + 1 (clipping stage) + 2 (push-pull output stage) for a total of of 6 tubes in the amp, although some tubes provide two separate channels in one package so the number of physical tubes found might be smaller.
Also, there are certain advantages to design rectifier bridges using tubes (the "standard" solution would use diodes instead, BertKoor mentioned this too since the rectifier would be part of the PSU), a tube based-rectifer would add another four tubes to the amp (I would guess that other parts of the PSU might utilize tubes instead of more modern components, but I'm not sure about this).
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- KVRist
- 234 posts since 11 May, 2005
I would have thought using a valve rectifier would simply require a single rectifier valve? any PSU schematics only seem to requre transistors or a valve for the rectifier, everything else being passive components.pilgrim_heart wrote:a tube based-rectifer would add another four tubes to the amp (I would guess that other parts of the PSU might utilize tubes instead of more modern components, but I'm not sure about this).
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- KVRist
- 187 posts since 20 Jul, 2004
Damnit! I just noticed that none of us really answered your actual question, eheheh...
The effect on sound from use of tubes will vary wildly depending on where they are utulizid. If you have a unit with just one tube I'd say it's reasonable to assume that this is used for clipping which can be nice but it wouldn't exactly give what people might refer to as "tube sound".
In tube stages designed not to clip (e.g. in mic preamps) the use of tubes shouldn't really produce a very different sound at all from other solutions if properly designed. One thing I've speculated about though is whether tubes might make a difference anyway when working with "untamed" signals whith a lot of short peaks since these peaks might produce clipping momentarily which tubes would generally handle more gracefully than transistors or OP-amps.
In guitar amps the "tube sound" would usually result from certain compressor-like effects that arise primarily in the output stage, for example many such designs will be "flawed" in that their input impedance will start decreasing if the stage is driven to hard. Another possible source of compression can occur in amps using tube-based rectifier bridges, if the output stage tries to draw more current than the rectifier can deliver it compression will occur (a diode-based rectifier would not be able to handle this and would be destroyed).
Tube based output stages will usually be isolated with transoformers, and these also colour the sound in certain ways which I would guess would be part of what people refer to as "tube sound".
The effect on sound from use of tubes will vary wildly depending on where they are utulizid. If you have a unit with just one tube I'd say it's reasonable to assume that this is used for clipping which can be nice but it wouldn't exactly give what people might refer to as "tube sound".
In tube stages designed not to clip (e.g. in mic preamps) the use of tubes shouldn't really produce a very different sound at all from other solutions if properly designed. One thing I've speculated about though is whether tubes might make a difference anyway when working with "untamed" signals whith a lot of short peaks since these peaks might produce clipping momentarily which tubes would generally handle more gracefully than transistors or OP-amps.
In guitar amps the "tube sound" would usually result from certain compressor-like effects that arise primarily in the output stage, for example many such designs will be "flawed" in that their input impedance will start decreasing if the stage is driven to hard. Another possible source of compression can occur in amps using tube-based rectifier bridges, if the output stage tries to draw more current than the rectifier can deliver it compression will occur (a diode-based rectifier would not be able to handle this and would be destroyed).
Tube based output stages will usually be isolated with transoformers, and these also colour the sound in certain ways which I would guess would be part of what people refer to as "tube sound".
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- KVRist
- 187 posts since 20 Jul, 2004
NoBrain2k:
Hmm, I guess this might be true. I'm far from an expert on these matters so there's probably tons of shit I don't know and have missed here. My immediate guess would be that there are certain tubes designed to provide a complete rectifier bridge in one package (using for channels in one tube) but I would not exclude the possibility of there being other reasons that I simply haven't heard about.
Hmm, I guess this might be true. I'm far from an expert on these matters so there's probably tons of shit I don't know and have missed here. My immediate guess would be that there are certain tubes designed to provide a complete rectifier bridge in one package (using for channels in one tube) but I would not exclude the possibility of there being other reasons that I simply haven't heard about.
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- KVRist
- 187 posts since 20 Jul, 2004
Think I might have found the answer (or more probably one of a number of possible answers), wikipedias article on rectifiers http://en.wikipedia.org/wiki/Rectifier has a schematic of a fullwave rectifier using one dual-anode tube. Looks pretty cool.
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- KVRAF
- 8389 posts since 11 Apr, 2003 from back on the hillside again - but now with a garden!
nice thread 
DSP
DSP
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- KVRAF
- 6478 posts since 16 Dec, 2002
[note, I'm only talking about preamps here]camsr wrote:I didn't know that before. What does using more than one tube do for the sound?
quite the blanket question. in traditional design number of tubes would be directly correlated to amount of gain really, and will not affect the sound mentionably. More tubes would be needed for higher output driving capability. Note, that does *not* mean drive as in distortion, but "driving" the impedance of the output transformer and output.
A great tube amp basically has no sound, but simply superior audio reproduction compared to opamps an transistor designs.
Depending on the design topology 3-5 tubes is pretty much the average for a good clean sound and linear gain, say 3 gain stages (usually feedback based) and a cathode follower to increase output driving capabilities, add a few more for push-pull (which is highly unnecessary in preamps for example). Tube rectifiers are rarely used these days in PSUs. In reality this means 2-3 tubes for a good preamp, as most of the time dual tubes are used (ie. two in one tube).
I'll have to repeat this as the current market has completely distorted the meaning of tube (pre)amp: A great tube preamp basically has no sound, but simply superior audio reproduction.
If we do away with feedback stages in the amp, the tube will act more "true to it's nature" and more non-linear distortion will be produced (more gain as well in fact). This is highly unorthodox in great preamps though, as goal will generally be clear linear sound.
Generally people don't know this, but in hi-end tube preamp designs the step-up and step-down transformers are usually the two parts that affect the sound most, and they can be quite expensive (some designs feature interstage trafos as well but these are generally esoteric and unnecessary topologies nowadays). The step-up and step-down trafos are also quite necessary as tubes work at such high potential compared to mere mic and line signals, and as we generally want a balanced output.
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- Banned
- 1149 posts since 7 Mar, 2004
Transformers and the way they are driven.
My JCM 800 was modded with a solid state rectifier for punch, i left there old the tube one so i can switch bettwen both.
Also cabinets are a major factor on how they sound. Hook a tiny 100watt 30th anniversary combo to a 4x12 closed back cabinet and you get a whole different beast.
the thing with the tubes is quite simple: its distottion is musical because the overtones (harmonics) enhanced are the fifths oposed to solid state wich enhances major thirds producing a less musical effect... i would say defect.
Another issue is the dynamic response of tubes wich makes then a lot more versatile.
Tubes are also used to drive spring reverbs, modern designs with multi channel pres use more tubes for cascading them, ence the possibility of generating huge amount of gain or bounce bettwen different channels.
My JCM 800 was modded with a solid state rectifier for punch, i left there old the tube one so i can switch bettwen both.
Also cabinets are a major factor on how they sound. Hook a tiny 100watt 30th anniversary combo to a 4x12 closed back cabinet and you get a whole different beast.
the thing with the tubes is quite simple: its distottion is musical because the overtones (harmonics) enhanced are the fifths oposed to solid state wich enhances major thirds producing a less musical effect... i would say defect.
Another issue is the dynamic response of tubes wich makes then a lot more versatile.
Tubes are also used to drive spring reverbs, modern designs with multi channel pres use more tubes for cascading them, ence the possibility of generating huge amount of gain or bounce bettwen different channels.
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- KVRist
- 230 posts since 27 Oct, 2005
I welcome anyone who would like to learn how to design and build tube amps to visit AX84.com- a site I created in 1998 to promote such things.
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- Rad Grandad
- 38041 posts since 6 Sep, 2003 from Downeast Maine
great post, it's been explained to me several times that guitar rigs boasting one tube (like digi-tech stuff) will not produce the same clipping as two or more tubes. However there is a "warmth" created by my Presonus Blue Tube on vox, but overdriven it doesn't cut it.pilgrim_heart wrote:Damnit! I just noticed that none of us really answered your actual question, eheheh...
The effect on sound from use of tubes will vary wildly depending on where they are utulizid. If you have a unit with just one tube I'd say it's reasonable to assume that this is used for clipping which can be nice but it wouldn't exactly give what people might refer to as "tube sound".
In tube stages designed not to clip (e.g. in mic preamps) the use of tubes shouldn't really produce a very different sound at all from other solutions if properly designed. One thing I've speculated about though is whether tubes might make a difference anyway when working with "untamed" signals whith a lot of short peaks since these peaks might produce clipping momentarily which tubes would generally handle more gracefully than transistors or OP-amps.
In guitar amps the "tube sound" would usually result from certain compressor-like effects that arise primarily in the output stage, for example many such designs will be "flawed" in that their input impedance will start decreasing if the stage is driven to hard. Another possible source of compression can occur in amps using tube-based rectifier bridges, if the output stage tries to draw more current than the rectifier can deliver it compression will occur (a diode-based rectifier would not be able to handle this and would be destroyed).
Tube based output stages will usually be isolated with transoformers, and these also colour the sound in certain ways which I would guess would be part of what people refer to as "tube sound".
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