How would pure power tube distortion sounds like?

[thinkingchicken]

Yes, but with the caveat that the Express blended distortion is in a way that is like no other amp. When the Express is in its sweet zone, the top half of the output waveform is pure EL34 power stage clipping and the bottom half is pure PI clipping underneath the power grid clipping threshold. That's why as raised in the other thread that when overdriven, one power valve in the Express is working really hard and the other isn't. That's because one is overdriven into grid clipping and the other is not. If you overdrive a Plexi far enough, the PI distortion overlays on the power valve distortion on both sides of the waveform.

Oh I see that's why you only mentioned Marshall 18 watt but not the Plexi when you're talking about which amp produced a pure power tube distortion. There is no question Trainwreck Express amps are so unique compared to the other amps. I just remember that Trainwreck amps are intentionally designed to mismatch the power tubes so the power tubes will clip first. Phase inverter distortion sounds just like the preamp distortion if I'm not mistaken so I can see that's why it sounds more aggressive than the power tube distortion. I just compared the distorted sounds of cranked Marshall 18 watt to some overdrive pedals on Youtube by listening to them.

The Express amp topology has a higher gain (as in voltage signal multiplication) between the input and the power grids than say a Plexi. So it can overdrive the power stage more (longer time in class AB1 grid clipping per cycle). That's nothing to do with the blended distortion. To get a Plexi to sound more distorted you need to drive it harder (upfront boost) or modify it to have more gain between the input jack and the power grids. But the amp topology is such so that will only go so far before other stages (PI and then the preamp) will overdrive. That will make more distortion of course, but blended rather than pure power stage.

Is there a gain limit to how much pentodes such as EL34 and EL84 can handle? I mean if we drive EL34 and EL84 to maximum, what will they sound like? Is a Trainwreck Express already reached the maximum gain possible for EL34? How extreme will EL34 and EL84 output tubes distorted if we keep increasing the gain? Can they actually reach the aggression of a typical high gain distortion of a solid-state electronics or preamplifier tubes that are abundant in harsher forms of rock music such as modern metal or punk music for example like this https://youtu.be/nxRe99Tjlwg and https://youtu.be/u09wrNjMA1g solely on their own without the aids of PI and preamp tubes and just by increasing maximum possible gain between the input jack and the power grids (or by setting the screen compression up to the highest maximum), or is the pure power tube distortion of Marshall 18 watt the true representation of absolute limit for extremely high gain power tube distortion thus the only way for EL34 and EL84-based non-master volume amps to have such distortion is by adding solid-state electronics and preamplifier tubes?

It's all about the clipping curve or transfer characteristic. As I said before my favourite amps use real pentodes and have them set up for a fair amount of screen compression leading into clipping. This is different to compression like from a compressor, which is like a form of averaging automatic gain control. Screen compression acts every cycle without an averaging effect, and softens the transition into grid clipping which can be seen in the waveform. Beam tetrodes don't draw the same screen current leading up to and in grid clipping, so they don't have as much screen compression effect. A Fuzz Face has none. When comparing square waves, you've got to zoom in on the corners and see how sharp/soft they are. That equates to a difference in harmonic content that doesn't look like much but makes a big difference in tone. Actual tone shaping of the amp or pedal circuit before and after the clipping is another factor on top of this as well that can change the tone completely.

What makes preamp tubes such as 12AX7 to be more aggressive when it comes to distortion compared to power tubes such as EL34, EL84 and the others? Out of all these components between preamp tubes, phase inverters, power tubes and solid-state components, which one of them can or will produce the loudest possible highest gain distortion sound in any amp at their maximum? I believe one of them will sound very harsh if they reach the maximum gain which make them more favorable to the heavy metal and hardcore punk fans.

[brewdude]

I think there is some confusion with regard to terms—gain is not the same as distortion.

[thinkingchicken]

I think there is some confusion with regard to terms—gain is not the same as distortion.

Isn't it that in order for power tubes to be very hard clipped or very distorted sounding at their most maximum, more gain should be applied?

[brewdude]

I would say that one increases distortion by increasing gain, but to me gain is more like signal “volume“ which may raise the distortion level. The problem to me is that when guitarist think “high gain“, they are usually talking about high distortion generated somewhere in the preamp of a master volume amplifier.

Gain is an increase of signal level (clean) that can generate overdrive (clipping) further downstream.

[katopan]

Good point Brew and thanks for the clarification. Other things come into play too, like available headroom. Say you design some LTP PI variant that somehow has massive gain. But if the maximum output signal swing available isn't enough to overdrive the power grids, you won't get power stage distortion from the massive gain driving into it.

[katopan]

Is there a gain limit to how much pentodes such as EL34 and EL84 can handle? I mean if we drive EL34 and EL84 to maximum, what will they sound like? Is a Trainwreck Express already reached the maximum gain possible for EL34? How extreme will EL34 and EL84 output tubes distorted if we keep increasing the gain? Can they actually reach the aggression of a typical high gain distortion of a solid-state electronics or preamplifier tubes that are abundant in harsher forms of rock music such as modern metal or punk music for example like this https://youtu.be/nxRe99Tjlwg and https://youtu.be/u09wrNjMA1g solely on their own without the aids of PI and preamp tubes and just by increasing maximum possible gain between the input jack and the power grids (or by setting the screen compression up to the highest maximum), or is the pure power tube distortion of Marshall 18 watt the true representation of absolute limit for extremely high gain power tube distortion thus the only way for EL34 and EL84-based non-master volume amps to have such distortion is by adding solid-state electronics and preamplifier tubes?

In Class AB1 where you aren't driving any significant current into the power grids in clipping, driving harder just means a bigger clean signal swing going into them, so after the grid clipping the signal just spends more time in the clipped region. ie. Steeper slope on the vertical bits of the square wave. In theory there is no limit to this. In practice the valve has a rating that will eventually be exceeded, but also you can only get so much signal swing out of a phase inverter before it starts to clip. One of the reasons why an 18 Watt has the EL84s so overdriven by the time the PI starts to clip that it doesn't matter is the available signal swing out of the PI vs. the EL84 grid clipping threshold (same as its grid to cathode bias voltage - something around 12V). Compare that to a Plexi where the output of the PI isn't that much greater (the PI supply rail voltage) but the EL34 bias and therefore grid clipping threshold might be something like 35V. Straight away a Plexi power stage not only has less gain available (as in clean voltage multiplication) but also less overdrive into the power grids before the PI runs out of clean headroom (available output swing). Getting more output swing from the PI becomes impossible due to PI valve rating and the fact that the PI power node is derived from the main HT supply, and therefore can't be higher than the power valve plates and screens anyway.

What makes preamp tubes such as 12AX7 to be more aggressive when it comes to distortion compared to power tubes such as EL34, EL84 and the others? Out of all these components between preamp tubes, phase inverters, power tubes and solid-state components, which one of them can or will produce the loudest possible highest gain distortion sound in any amp at their maximum? I believe one of them will sound very harsh if they reach the maximum gain which make them more favorable to the heavy metal and hardcore punk fans.

Their transfer characteristic, the fact that the cut-off side of the waveform sounds different to the grid clipping side, the smaller clipping threshold compared to the available output signal swing.

Any amp is loudest when the power stage is being overdriven. Otherwise clipping is occurring at a lower than maximum output power to the speaker.

Highest gain distortion sound can be produced by any stage, it just depends on what tone you want. The more distortion, the harder it is to get it to sound good. Even the heaviest metal bands use less distortion live than what most people think of when they think brutal tones. A lot of it has to do with pre-distortion and post-distortion EQ.

Modern metal tones are proven to be best created with preamp valves and/or solid state, most often with a very clean or only slightly overdriven output stage. There are plenty of designs to reference. Hardcore punk, modern metal and vintage metal are all different tones made in different ways.

[thinkingchicken]

In Class AB1 where you aren't driving any significant current into the power grids in clipping, driving harder just means a bigger clean signal swing going into them, so after the grid clipping the signal just spends more time in the clipped region. ie. Steeper slope on the vertical bits of the square wave. In theory there is no limit to this. In practice the valve has a rating that will eventually be exceeded, but also you can only get so much signal swing out of a phase inverter before it starts to clip. One of the reasons why an 18 Watt has the EL84s so overdriven by the time the PI starts to clip that it doesn't matter is the available signal swing out of the PI vs. the EL84 grid clipping threshold (same as its grid to cathode bias voltage - something around 12V). Compare that to a Plexi where the output of the PI isn't that much greater (the PI supply rail voltage) but the EL34 bias and therefore grid clipping threshold might be something like 35V. Straight away a Plexi power stage not only has less gain available (as in clean voltage multiplication) but also less overdrive into the power grids before the PI runs out of clean headroom (available output swing). Getting more output swing from the PI becomes impossible due to PI valve rating and the fact that the PI power node is derived from the main HT supply, and therefore can't be higher than the power valve plates and screens anyway.

Ok let see if I understand what you're saying, a Trainwreck Express is only producing pure output valve distortion until we drive the volume pass 12 o'clock where the PI and the third preamp stage started to change in waveforms. Correct? What is the function of the third preamp stage when we started to overdrive the power amp? Does it act as a clean boost?

I never play an EL34 Trainwreck Express in person, I just watched some demo of it and it sounds different from Marshall 18 watt especially when the volume pass 12 o'clock. People always thought someone put a fuzz or an overdrive pedal into the TW Express but as we already understand, pass 12 o'clock on volume the TW Express is always producing blended distortion after that. Some people even thought the distorted sound of Trainwreck Express especially with the volume pass 12 o'clock is purely output valve distortion but then I listened to fully cranked Marshall 18 watt and it sounds nothing like that.

So despite the higher gain of TW Express, in terms of pure output valve distortion, does it sounds basically the same as the output valve distortion sound of Marshall 18 watt even if we overdrive it beyond its limit? I never heard the TW Express producing distortion purely from the output valves so far.

Their transfer characteristic, the fact that the cut-off side of the waveform sounds different to the grid clipping side, the smaller clipping threshold compared to the available output signal swing.

Any amp is loudest when the power stage is being overdriven. Otherwise clipping is occurring at a lower than maximum output power to the speaker.

Highest gain distortion sound can be produced by any stage, it just depends on what tone you want. The more distortion, the harder it is to get it to sound good. Even the heaviest metal bands use less distortion live than what most people think of when they think brutal tones. A lot of it has to do with pre-distortion and post-distortion EQ.

Modern metal tones are proven to be best created with preamp valves and/or solid state, most often with a very clean or only slightly overdriven output stage. There are plenty of designs to reference. Hardcore punk, modern metal and vintage metal are all different tones made in different ways.

Speaking in layman's terms, if I strictly want to get that modern metal high gain distortion tone by using EL34 Trainwreck Express amps or clones, there is no way I can get the tone of modern metal by only relying on the distortion of the EL34 itself even if someone had modified it to have highest maximum gain between the input jack and the power grids so I have to drive it to the max where blended distortion of output valves, PI and third preamp stage eventually happens and then put a distortion or boost pedal into it? Isn't it?

No matter how high the gain is available for output valves i.e EL34 or EL84, is the distorted output valve sound always going to sounds like those of Marshall 18 watt? Remember, here we are talking about purely output valves and this excluded the PI and preamp stages.

[brewdude]

It seems to me that if you are looking for modern metal sounds, “pure power amp” distortion is probably not the right goal. I would think that a clean, strong, loud power amp with lots of headroom, and a thoughtfully designed cascaded multistage preamp (or a well chosen pedal) would work better.

[thinkingchicken]

It seems to me that if you are looking for modern metal sounds, “pure power amp” distortion is probably not the right goal. I would think that a clean, strong, loud power amp with lots of headroom, and a thoughtfully designed cascaded multistage preamp (or a well chosen pedal) would work better.

I see. So, a power tube (or valve) distortion alone no matter if it is modded to have the highest gain ever for power tube distortion will never going to give a high gain distorted 90s to 2000s or basically modern metal tone. From what I've just learned when I saw a statement in some forums "typically in an EL34 amp running the plates from 400 to 460 volts, the power tubes when the speaker impedance is matched, want to see a primary resistance of 3.4 to 3.6K. On Trainwrecks, Ken used 6.6K primaries which is similar to plugging into a cab one step impedance higher. So in a nutshell Trainwreck EL34's see impedance of 8,16,and 32 ohms when plugged into 4,8,16 ohm cabs. This results in a loss of power output (35 watts) but results in more mids and upper mid emphasis and harmonic overtones".

That means the lower the watt, the more distorted the power valve tones? Does that also means just because the 100 watt amp is much higher in gain than the lower watt amp, it doesn't mean that the 100 watt amp is going to be more distorted than the lower watt amp?

[thinkingchicken]

Another thing to add, "The secret to a Trainwreck is the output transformer. The impedance ratio is about twice that of other amps. I.e. typical 50W Marshall has a primary impedance of about 3200 ohms. A Trainwreck is about 6500 ohms. The causes the power tubes to clip much sooner."

What is the highest possible impedance ratio for EL34 Trainwreck Express amps?

[brewdude]

Wattage rating on a tube power amp is a measure of how loud it can get before it begins to distort. It is not a measure of how distorted it can get.

[thinkingchicken]

Wattage rating on a tube power amp is a measure of how loud it can get before it begins to distort. It is not a measure of how distorted it can get.

But at lower watt, the breakup happens much sooner compared to higher watt amps.

[brewdude]

At lower volume

[statorvane]

I've never heard a Marshall 18 Watt or Trainwreck Express / Liverpool in person, only audio clips on YouTube. However, I built a clone Marshall 2061X - with slightly reduced plate voltage at 350 VDC. Pretty sure with one triode of gain into the a PI, then EL84 tubes, what I am hearing cranked is power tube distortion. Maybe some PI contribution there, but in any case this little monster really screams. Sounds very cool. With the simple volume / tone control of the lead channel and large bright cap, setting the tone on "10" and the volume on "1" it really cranks. As the volume is increased the tone fattens up and adds a little more volume. The two are really interactive in a good way I think. The sound is frankly glorious. I'm not much of a player, but when my son plugs into it - holy cow....

You can hear Phil's team demonstrate it - jump to around 04:40: https://www.youtube.com/watch?v=JAajlPABSHA Even the drummer was impressed.

I'll have to dig out the scope and see what it really going on there.

[thinkingchicken]

Is there a gain limit to how much pentodes such as EL34 and EL84 can handle? I mean if we drive EL34 and EL84 to maximum, what will they sound like? Is a Trainwreck Express already reached the maximum gain possible for EL34? How extreme will EL34 and EL84 output tubes distorted if we keep increasing the gain? Can they actually reach the aggression of a typical high gain distortion of a solid-state electronics or preamplifier tubes that are abundant in harsher forms of rock music such as modern metal or punk music for example like this https://youtu.be/nxRe99Tjlwg and https://youtu.be/u09wrNjMA1g solely on their own without the aids of PI and preamp tubes and just by increasing maximum possible gain between the input jack and the power grids (or by setting the screen compression up to the highest maximum), or is the pure power tube distortion of Marshall 18 watt the true representation of absolute limit for extremely high gain power tube distortion thus the only way for EL34 and EL84-based non-master volume amps to have such distortion is by adding solid-state electronics and preamplifier tubes?

In Class AB1 where you aren't driving any significant current into the power grids in clipping, driving harder just means a bigger clean signal swing going into them, so after the grid clipping the signal just spends more time in the clipped region. ie. Steeper slope on the vertical bits of the square wave. In theory there is no limit to this. In practice the valve has a rating that will eventually be exceeded, but also you can only get so much signal swing out of a phase inverter before it starts to clip. One of the reasons why an 18 Watt has the EL84s so overdriven by the time the PI starts to clip that it doesn't matter is the available signal swing out of the PI vs. the EL84 grid clipping threshold (same as its grid to cathode bias voltage - something around 12V). Compare that to a Plexi where the output of the PI isn't that much greater (the PI supply rail voltage) but the EL34 bias and therefore grid clipping threshold might be something like 35V. Straight away a Plexi power stage not only has less gain available (as in clean voltage multiplication) but also less overdrive into the power grids before the PI runs out of clean headroom (available output swing). Getting more output swing from the PI becomes impossible due to PI valve rating and the fact that the PI power node is derived from the main HT supply, and therefore can't be higher than the power valve plates and screens anyway.

What makes preamp tubes such as 12AX7 to be more aggressive when it comes to distortion compared to power tubes such as EL34, EL84 and the others? Out of all these components between preamp tubes, phase inverters, power tubes and solid-state components, which one of them can or will produce the loudest possible highest gain distortion sound in any amp at their maximum? I believe one of them will sound very harsh if they reach the maximum gain which make them more favorable to the heavy metal and hardcore punk fans.

Their transfer characteristic, the fact that the cut-off side of the waveform sounds different to the grid clipping side, the smaller clipping threshold compared to the available output signal swing.

Any amp is loudest when the power stage is being overdriven. Otherwise clipping is occurring at a lower than maximum output power to the speaker.

Highest gain distortion sound can be produced by any stage, it just depends on what tone you want. The more distortion, the harder it is to get it to sound good. Even the heaviest metal bands use less distortion live than what most people think of when they think brutal tones. A lot of it has to do with pre-distortion and post-distortion EQ.

Modern metal tones are proven to be best created with preamp valves and/or solid state, most often with a very clean or only slightly overdriven output stage. There are plenty of designs to reference. Hardcore punk, modern metal and vintage metal are all different tones made in different ways.

Take a look at this quote I got from a different forum,

"In some respects, a tube is just a tube: we could cascade 5 or 6 EL34s in a preamp-like circuit to mimic a master-volume preamp, where each stage contributes a little distortion per stage to build up a smooth high-gain sound (just like a Mesa preamp, or a SLO preamp, or a Marshall preamp, etc). Nobody does this because it would cost a lot more than using the usual small-signal preamp tubes, power supply requirements would be obscene, and a preamp for our "power-tube preamp" would be required to get signal levels large enough to drive each tube to distortion."

Given that we have enough power supply requirements and enough signal levels to drive each EL34 to extreme distortion, will it actually produce a similar high gain preamp distortion sounds that are produced by modern Mesa preamps and other high gain amps despite the differences in characteristics between pentodes and triodes?