Is it possible to get output tube’s harmonic overtone

[Bman]

I don’t know if I’m describing the ‘phenomenon’ technically correct. When my tube amps have been cranked and the tubes are hot I get these overtones that I’ve yet to really hear in any of the modeler clips. Just wondering if that’s possible.

 

[Rex]

I don’t know if I’m describing the ‘phenomenon’ technically correct. When my tube amps have been cranked and the tubes are hot I get these overtones that I’ve yet to really hear in any of the modeler clips. Just wondering if that’s possible.

Without hearing a clip, it's hard to answer your question. There's no way to tell if you're talking about feedback, oscillation, microphonics, clipping, or...?

The tube modeling is wickedly accurate. Can you provide a sample of what you're talking about?

 

[chris]

I don’t know if I’m describing the ‘phenomenon’ technically correct. When my tube amps have been cranked and the tubes are hot I get these overtones that I’ve yet to really hear in any of the modeler clips. Just wondering if that’s possible.

were you near your amp and was the volume loud at the time?

 

[Sixstring]

Sounds like he is describing power tube distortion opposed to preamp. If that's the case just turn up the master in the amp sim, Anything over 5 on the knob starts to add this sound you are describing.

Simple way to hear the difference is to lower the preamp gain setting and crank the master volume. In most amp sims that have a MV you will hear a different sounding distortion.

 

[Rex]

Sounds like he is describing power tube distortion opposed to preamp.

Maybe. There are a lot of ways to interpret what he's saying.

 

[Bman]

It's difficult for me to describe. The amp or amps have been cranked to rehearsal levels. I am standing close enough to the amp to feed back but this doesn't happen early on when the amp hasn't been running for a while. It's only after the amp has been pushed loud for an hour or more. It's sounds like some overtones, especially when holding back on the guitar volume. The amp feels like it's being restrained but the tone that results has something 'special'. Both amps are Marshalls - EL34s.

I can sort of hear it in the tones of:

Angus -Back In Black (I've read that there was some accidental goodness that happened that pushed his amp a bit more).
Ritchie Blackmoore - Stone Cold (Marshall Major 200 watts... plays with his fingers and guitar volume varies)
Joe Bonamassa - Plays with 2 amps going, so that's a little tough. Always has a jubilee's pre-amp dist. going on though. But LOUD. A lot of headroom.


All 3 above are playing EL34 amps very loud. It could be an interaction with the pickups and amp but I've always noticed it about 1 or 2 hours into rehearsal. It's not ear fatigue either (I hope). Anyway, it's not something I'll be chasing with the AX8 because I believe it probably is relative to being in the room with a loud amp and the tubes are hot (I don't mean biased that way). I'll take a JTM or SuperLead model and crank the master and see if I can reproduce the condition. My mom's in town and I can't do jack-sh... for a week. I probably have no business posting since I can't go back and apply anything. I guess that's a high class problem, huh? No AX8 for a week!

 

[FractalAudio]

Tinnitus?

 

[Bman]

That or schizophrenia

 

[speedloader]

The tube modeling is wickedly accurate.

This, I must disagree with. Too little difference between tubes. If you swap real tubes it's often night and day. Load your preamp with JJs ECC83, then Tung sols 12AX7, first will be much more middy, muddy, creamy and biting, last will give much more gain, fizzier and colder, glassy. And the sovteks are kinda flat in the mids like the tung sol with more solid low mids and a darker top end (no ice peaks), more like the JJs yet with uncompressed, unbiting mids.. When I swap the virtual tubes, almost nothing changes, even when listening through a real cab. Maybe in the end, those tubes sound like tubes, but.. changing the tubes show that there's a significant room for improvement.

 

[Rex]

This, I must disagree with. Too little difference between tubes. If you swap real tubes it's often night and day.

That’s because, in Fractal products, the virtual circuitry is automaticall6 changed to accommodate the tubes you’re using. You don’t get that with a real amp; if you change out physical tubes in a real amp, you’re puttin* 5he new tubes into circuitry thats mismatched because it was designed for the original tubes.

 

[Rex]

It's difficult for me to describe. The amp or amps have been cranked to rehearsal levels. I am standing close enough to the amp to feed back but this doesn't happen early on when the amp hasn't been running for a while. It's only after the amp has been pushed loud for an hour or more.

If you only get feedback after your amp has warmed up, then your amp is increasing its gain when it gets hot. The AX8 can be set up to give you that feedback right away. No need to wait an hour for it to sound right.

 

[speedloader]

That’s because, in Fractal products, the virtual circuitry is automaticall6 changed to accommodate the tubes you’re using. You don’t get that with a real amp; if you change out physical tubes in a real amp, you’re puttin* 5he new tubes into circuitry thats mismatched because it was designed for the original tubes.

Can Cliff confirm that? Then what's the point of having the choice if the circuit changes to make tubes sound the same? Sounds fishy honestly. The point of changing tubes is to change the tone. Plenty of amps benefit from changing the stock tubes for another combination. I'd rather put Tung Sols in an Atomica, JJs in a Deliverance... and hear the improvement.

 

[Bman]

If you only get feedback after your amp has warmed up, then your amp is increasing its gain when it gets hot. The AX8 can be set up to give you that feedback right away. No need to wait an hour for it to sound right.

When I think of feedback I think about the result of standing next to a loud amp and the amp squealing or singing...either way it’s the interaction between the pickups or a microphone and an amp/speaker. This would NOT be what I’m talking about.

Is there a more technical definition of feedback other than the obvious one that comes to mind?

 

[Rex]

When I think of feedback I think about the result of standing next to a loud amp and the amp squealing or singing...either way it’s the interaction between the pickups or a microphone and an amp/speaker. This would NOT be what I’m talking about.

Is there a more technical definition of feedback other than the obvious one that comes to mind?

We need a recording of what you're talking about. Without that, we're grasping at straws.

 

[Rex]

Can Cliff confirm that? Then what's the point of having the choice if the circuit changes to make tubes sound the same? Sounds fishy honestly. The point of changing tubes is to change the tone. Plenty of amps benefit from changing the stock tubes for another combination. I'd rather put Tung Sols in an Atomica, JJs in a Deliverance... and hear the improvement.

You'll often read that 6L6's sound "full" whereas EL34's have more midrange and other colloquial descriptions of the tone of a power tube. These myths are perpetuated by forum dwellers, uninformed tube "experts" and even amp manufacturers as marketing tools.

Well, the fact is that power tubes do NOT sound different. They do not have any intrinsic tone.

"But I can hear the difference when I change to a different type of power tube. How can that be?"

A power tube has a very flat frequency response and they all clip roughly the same. If you put a resistive dummy load on a tube power amp (assuming it doesn't have any intentional frequency shaping) it will measure very flat. However a speaker is not a resistive load. A speaker is a highly reactive load. As I've mentioned in the other threads in this forum section a speaker has an impedance that is sort of scooped at the midrange frequencies.

It is the impedance of the speaker that affects the tone of the amp and different types of power tubes react differently with that impedance. As I've mentioned before a power tube is nearly a current source. The operative word here is "nearly". No power tube has an infinite plate impedance and that's why power tubes sound different. A current source has infinite output impedance, an actual power tube has a finite output impedance.

The output impedance of a power tube (or any active device for that matter) is defined as delta V / delta I which is the change in voltage vs. the change in current.

Let's take a 6L6 for example. Let's assume that the tube has a quiescent operating point of 300V and let's assume we swing +/- 100V around that point. If we look at the plate graphs for a 6L6 at a bias of -10V we see that the plate current at 200V is 95 mA and at 400V it's 105 mA (roughly). Using our formula for impedance we get 200/0.01 = 20 Kohms.

Now let's take an EL34. At 200V the current is 130 mA and at 400V the current is 150 mA. The plate impedance is therefore 10 Kohms which is half that of the 6L6.

This lower output impedance "de-Q's", or flattens, the speaker impedance. Essentially the EL34 has a higher damping factor than a 6L6. This higher damping factor reduces the mid-scoop due to the speaker impedance. This makes the tone have more midrange.

There's a little more to it as the output transformer plays a role as well and 6L6 power amps typically have a slightly higher impedance ratio. There's also different operating voltages and bias points but I'm trying to keep this simple.

You can simulate changing power tubes in the Axe-Fx by simply increasing or decreasing the LF and HF resonance values.

 

[speedloader]

Funny because I swapped them myself frequently enough to hear the difference. Being an ex MTS user at least taught me about the effect of tubes and cap/transistor materials on tone.

I don't care if tubes have any intrinsic tonal difference. That's plying with words. What they do to the circuit is more than what swapping virtual tubes and tweaking the preamp hardness do in the models.

Furthermore, I'm talking about preamp tubes. Not power amp tubes.

 

[Smittefar]

He's not really talking about that. He is talking (writing) about changing to the same type of tubes. In the preamp section, we get the choice between 4? different 12AX7/ECC83 tubes. I hear very little difference, when I switch between these 4? types. On the other hand I heard big differences in tonality on my real tube amps, when I switched preamp tubes - I should mention that most often, I have switched from factory installed Chinese shit-tubes to NOS Mullards or something like that, so there should be a difference. But even between different good NOS tubes you can definitely hear a difference. I don't think the tube choice in AX8/AxeFX give the same kind of difference.

EDIT: My reply was to @Rex. "He" refers to @speedloader

 

[paulasbell]

In the preamp section, we get the choice between 4? different 12AX7/ECC83 tubes. I hear very little difference, when I switch between these 4? types.

I think it's fair to say that we guitarists are all are quite picky about certain tonal aspects, and somewhat "whatever" about others. I can say that for me, those preamp tube options are DEFINITELY different, and i find i have strong preferences between them.

But even between different good NOS tubes you can definitely hear a difference. I don't think the tube choice in AX8/AxeFX give the same kind of difference.

I'm guessing that the differences between "identical model" preamp tubes can be replicated with the many parameters we have adjustable in the preamp section. Certainly, changing those parameters (preamp hardness, etc) makes a noticeable difference for all of us?

In any case, and by the same token, I think Rex' response to speedloader is dead-on, and speedloader can certainly find those power tube differences he's looking for, by rolling up his sleeves and tweaking the many parameter options we've got available.

 

[Sixstring]

Maybe. There are a lot of ways to interpret what he's saying.

This is true! The first highlighted words indicates that he has the "phenomenon" in more than one amp and the second points to hot tubes, so it could be BIAS drift and though very possible I have never heard of this type of condition creating what the OP is describing. All kinds of things change inside of a hot amp and depending on how old it is it could be quite drastic.

Hummm, maybe something for Cliff to consider if he already has not done so.

I don’t know if I’m describing the ‘phenomenon’ technically correct. When my tube amps have been cranked and the tubes are hot I get these overtones that I’ve yet to really hear in any of the modeler clips. Just wondering if that’s possible.

 

[unix-guy]

Edit: the quoting is not showing the post but it's this one from @Rex :

https://forum.fractalaudio.com/threads/is-it-possible-to-get-output-tube’s-harmonic-overtone.133614/#post-1579901

To.make a distinction, that is really about power tubes and the related circuitry.whereas the post by @speedloader is talking about preamp tubes.

However, I think his comments are making lot of assumptions based on tube "brand" rather than the actual tube specifications.

For example, I've used a number of JJ ECC83 tubes and they are all different. Just swapping the same set of "identical" tubes into different positions in the preamp will affect the gain and tone.