No Differences When Changing Tubes?

luke said:
It’s not quite that simple. He is telling you there IS difference in tone, but the tube is not directly to blame. The tone shaping happens further down the signal path.
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I literally said power tubes don't have a sound, which is what Cliff said in the thread:

FractalAudio said:
Well, the fact is that power tubes do NOT sound different. They do not have any intrinsic tone.
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I didn't say anything else. I linked the thread that speaks for itself to explain the rest.

You are correct that different power tubes will potentially contribute to a change in tone by interacting with the rest of the circuit.

Also, that thread is a bit old and I am fairly certain it predates the ability to change power tube types in the Axe Fx II, so it also doesn't address some of the "normalization" that happens inside the unit when you change types.
 
Low listening volume is ok for bedroom playing and then, yes, you can't hear much of a change. But be aware that this way of tweaking isn't sufficent to play in a band. Once you play with a drummer in the room you need to crank the volume up enough to hear every tube's unique details.
Crank it up a bit?
 
666was999 said:
Low listening volume is ok for bedroom playing and then, yes, you can't hear much of a change. But be aware that this way of tweaking isn't sufficent to play in a band. Once you play with a drummer in the room you need to crank the volume up enough to hear every tube's unique details.
Crank it up a bit?
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Absolutely right. I haven't been in that situation since getting this unit and having to stay home all these months. That's a really fair point
 
I think what I'm hearing mostly in this thread is a combination of "power tubes don't have a tone" and "but you aren't setting up the amp properly to take advantage of the different tone the power tubes have." Those kind of seem contradictory.

Again, if the tubes themselves don't cause a change in tone or behavior, certainly within the circuit they do. And that's the point of changing power tubes. Nobody would expect an amp with EL84s in it to sound the same as if substituted KT88s in that circuit. It would change the tone and response pretty substantially. I still have a set of "Yellowjackets," sockets that let you run EL84s in an amp designed for 6L6s. The change is pretty notable. And yes, it's true that you have to compare apples to apples in terms of how hard you are driving the power amp section, and an edge-of-breakup 6L6 amp is louder than the same setting on EL84s, but not by as much as you might think. It's more about available headroom, IIRC.

I put in an item in the Wish List where I say I'd like for the corresponding circuit/setting changes to travel with the changes in power tubes if at all possible. Or at the very least a recipe for knowing what existing settings one should change when changing power tubes (change the grid bias shift? Change the transformer drive? What else?)
 
I think a good summary is this:
Power Tubes themselves all operate similarly, and behave in a very similar manner when under normal operating conditions.

Under extreme conditions like power amp distortion, the different distortion characteristics will be more noticeable.

But an amp designed to run clean with EL34s and an amp designed to run clean with 6L6s shouldn't have major tonal differences because of the tube types themselves.

Where the Axe differs from a real amp is that you can change one aspect of the power amp (the tubes themselves) without changing other behavioral parameters. You can magically swap from EL34s which are properly biased in a properly designed power amp to 6L6s which are properly biased and in a properly designed power amp. In a real amp it's not that easy: the power amp is designed to work ideally with one set of power tubes and despite being able to shift the bias for another type there are other things that behave differently.

So, what changes the sound when changing tube types in a real amp isn't the tubes themselves as much as the way they interact with the rest of the amp.

One of these is the behavior of the amp interaction with the speaker impedance. Larger peaks in the highs and lows can simulate switching to 6L6s, and smaller peaks (which sounds like more midrange in the final tone) to emulate switching to el34s.
 
IronSean said:
So, what changes the sound when changing tube types in a real amp isn't the tubes themselves as much as the way they interact with the rest of the amp.

One of these is the behavior of the amp interaction with the speaker impedance. Larger peaks in the highs and lows can simulate switching to 6L6s, and smaller peaks (which sounds like more midrange in the final tone) to emulate switching to el34s.
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This ^^^^

When you change the tube type, a big part of the different sound is the fixed output transformer plate impedance. Each type has a particular "best" plate load. EL34s like a bit lower load than 6L6, which is 'low-loaded' at 4.2k, where the EL34s like a 3.4k load. The AxeFX3 has both Speaker Impedance and XFormer Match knobs, which seem to correspond to mismatch on the secondary and primary side of the virtual output transformer, respectively. So, if you knew you were putting EL34s in a BF Super, you could tweak XFormer Match to 0.809 (3.4k/4.2k) and you'd be there. Plugging the Super's speaker out into a 2x12" Zilla cab? Tweak Speaker Impedance to 2.0 (4/2) and you're golden. It's nice having those on separate knobs. :) Having the 'authentic mode' calculate the tubes' ideal matching load vs. the amp's OT primary actual load and setting an internal impedance mismatch parameter for you (so that the XFormer match knob need not tweak itself off 1.0 for this) would be awesome. A chart somewhere with the various amps' OT primary impedances and the tubes' ideal loads would work, but require math on the end-user's part....

Bias enters into the equation as well, as different tubes have different bias requirements to set idle current at a safe and/or optimal level for the operating conditions. The bias voltage ultimately determines how much PI output it takes to fully drive the grids, and, where output grid clamping, bias shifting, etc. start to occur. BF Fenders and Mark series Boogies, for example, are usually biased a bit cooler, while some others are biased a bit hotter (and even a bit too hot for good tube life, in some cases). The negative grid voltage or cathode resistor required to produce a "cool 55%" or "warm 70%" idle varies quite a bit from tube type to tube type when operating conditions are held static (i.e., when swapping tubes in a particular amp). It's great for the average end-user to have an idealized percentage, as it takes a bit of the EE out of it while still giving a useful control. It'd be fun for us tweaker types (all 3 of us :D) to have the ideal mode back these values out to voltages or cathode resistor and capacitor values. Oh, to be able to dial in a 68 ohm Rk and 50uF cap on your AC30, or a -48V bias voltage on your BF Super, or something like that, though. Not a lot of people out there who would know what that means, though, so I am not expecting that it will get done.
 
greiswig said:
I think what I'm hearing mostly in this thread is a combination of "power tubes don't have a tone" and "but you aren't setting up the amp properly to take advantage of the different tone the power tubes have." Those kind of seem contradictory.

Again, if the tubes themselves don't cause a change in tone or behavior, certainly within the circuit they do. And that's the point of changing power tubes. Nobody would expect an amp with EL84s in it to sound the same as if substituted KT88s in that circuit. It would change the tone and response pretty substantially. I still have a set of "Yellowjackets," sockets that let you run EL84s in an amp designed for 6L6s. The change is pretty notable. And yes, it's true that you have to compare apples to apples in terms of how hard you are driving the power amp section, and an edge-of-breakup 6L6 amp is louder than the same setting on EL84s, but not by as much as you might think. It's more about available headroom, IIRC.

I put in an item in the Wish List where I say I'd like for the corresponding circuit/setting changes to travel with the changes in power tubes if at all possible. Or at the very least a recipe for knowing what existing settings one should change when changing power tubes (change the grid bias shift? Change the transformer drive? What else?)
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+1

I keep reading posts that rave about tube differences. See the link I posted above where Fractal and others express love of how good the 6CA7s are - i.e. in the jumped 50 Plexi model - but if I set up a simple amp/cab plexi patch and change the power tubes parameter to 6CA7 I hear no difference in tone or feel regardless of gain settings.

From what I can gather reading about this (i.e. the 2014 post from Fractal and posts here), my (and others) observation is to be expected as other parameters need to change along with the tube parameter in order to hear/feel differences one would normally expect with real world tube swaps.

So the obvious question is: what are those related parameter changes?, and what are the guidelines to setting them in relation to "tube changes" that
may be worthwhile doing? If the answer is (and I strongly suspect this is the case given the complexity of the explanations some have attempted), that it's too complex to be practical for most Axefx users to do, then granting the wish for "baking in the changes" somehow while
also leaving the individual parameters exposed for supertweakers would be a great alternative. If the wish can't be granted, and it's too complex to "teach it", then I kind of question the value of having the tubes parameter exposed since many (probably most) of us won't be able to "join the tubes appreciation party" due to lack of know how (and we'll continue to feel sad when the gurus express how wonderful various tube changes are 😩😩)
 
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sprint said:
+1

I keep reading posts that rave about tube differences. See the link I posted above where Fractal and others express love of how good the 6CA7s are - i.e. in the jumped 50 Plexi model - but if I set up a simple amp/cab plexi patch and change the power tubes parameter to 6CA7 I hear no difference in tone or feel regardless of gain settings.

From what I can gather reading about this (i.e. the 2014 post from Fractal and posts here), my (and others) observation is to be expected as other parameters need to change along with the tube parameter in order to hear/feel differences one would normally expect with real world tube swaps.

So the obvious question is: what are those related parameter changes?, and what are the guidelines to setting them in relation to "tube changes" that
may be worthwhile doing? If the answer is (and I strongly suspect this is the case given the complexity of the explanations some have attempted), that it's too complex to be practical for most Axefx users to do, then granting the wish for "baking in the changes" somehow while
also leaving the individual parameters exposed for supertweakers would be a great alternative. If the wish can't be granted, and it's too complex to "teach it", then I kind of question the value of having the tubes parameter exposed since many (probably most) of us won't be able to "join the tubes appreciation party" due to lack of know how (and we'll continue to feel sad when the gurus express how wonderful various tube changes are 😩😩)
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Make a wish list thread and I'll +1 that thing.
 
sprint said:
+1

I keep reading posts that rave about tube differences. See the link I posted above where Fractal and others express love of how good the 6CA7s are - i.e. in the jumped 50 Plexi model - but if I set up a simple amp/cab plexi patch and change the power tubes parameter to 6CA7 I hear no difference in tone or feel regardless of gain settings.

From what I can gather reading about this (i.e. the 2014 post from Fractal and posts here), my (and others) observation is to be expected as other parameters need to change along with the tube parameter in order to hear/feel differences one would normally expect with real world tube swaps.

So the obvious question is simply: what are those related parameter changes?, and what are the guidelines to setting them in relation to "tube changes" that
may be worthwhile doing? If the answer is (and I strongly suspect this is the case given the complexity of the explanation some have attempted), that it's too complex to be practical for most Axefx users to do, then granting the wish for "baking in the changes" would be a great alternative. If the wish can't be granted, and it's too complex to "teach it", then I kind of question the value of having the tubes parameter exposed since many
of won't be able to "join the tubes appreciation party" due to lack of know how.
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Sylvania '60s 6CA7 data:
http://tdsl.duncanamps.com/dcigna/tubes/sheets/sylvania/syl-143h.gif
http://tdsl.duncanamps.com/dcigna/tubes/sheets/sylvania/syl-144h.gif

Mullard EL34 data:
https://datasheetspdf.com/pdf-file/957555/Mullard/EL34/1

These are clearly the specs for the skinny EL34 type in both cases. Specs for the later US fat-bottle type are harder to find, as transistors were starting to eat market share from tubes, and the effort to put out detailed spec sheets for tubes was likely seen as 'not enough bang for the buck'....

6CA7s made in USA were generally a beam tetrode. Supposedly Sylvania was importing EL34s in the '60s from Phillips in Europe, but decided to stick different control and screen grids inside a 6L6 (or 6550, depending on who tells the story) plate/beam-former assembly to get similar bias requirements, and called it a 6CA7STR, so they didn't have to import the skinny Phillips EL34 pentodes. GE fat-bulb 6CA7s were similar. It is quite clearly visible by looking at the internal construction that it had beam-forming plates rather than a third grid for suppressor. Many data sheets show EL34/6CA7 as a pentode, while some show a beam tetrode, as a result. Lots of research to do to determine what the setting should be. It'd be nice to have this research baked into an 'authentic mode'. :)

EDIT: 25 year old anecdotal 6CA7 info from Vacuum Tube Valley: https://www.pearl-hifi.com/06_Lit_Archive/02_PEARL_Arch/Vol_16/Sec_53/VTV/02_01_Fall_1995.pdf

Finding designer-level specs on these old tube types is difficult, at best....
 
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Wow great explanations here.

The "normalized" design of the amp modeling (and exposed parameters) propably meets the vast majority of users' needs for tweaking. The more amp savvy and EE folks could play with raw values if exposed but that could open up a whole can of worms as to what are the "right" original values also also might result in circuit instabilities which the normalization approach probably minimizes (fewer headaches for FAS support).

Joe Bfstplk said:
Finding designer-level specs on these old tube types is difficult, at best....
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I imagine, if at all possible, Cliff measures actual tube parameters as opposed to using spec sheets (which probably leads to higher accuracy within modeling)?
 
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yyz67 said:
The "normalized" design of the amp modeling (and exposed parameters) propably meets the bast majority of users' needs for tweaking. The more amp savvy and EE folks could play with raw values if exposed but that could open up a whole can of worms as to what are the "right" original values also also might result in circuit instabilities which the normalization approach probably minimizes (fewer headaches for FAS support).
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475530936.0.x.jpg

Yes, I expect that this would be a true opening of Pandora's Can of Worms, on a scale much larger than the whoopsie with the modifier attachments recently. I don't expect it to be made available. If there was an internal scalar applied in "authentic" mode to offset the idealized impedance to be skewed to match the new tube type's difference from the model's expected tube, it could be safe (i.e., under FAS control) and still leave the user use of the XFormer Match control. Trust me when I say I know about letting unqualified personnel have access to controls that only developers should have. I do IT work.

Gotsta pay attention to the sign:

:D

yyz67 said:
I imagine, if at all possible, Cliff measures actual tube parameters as opposed to using spec sheets (which probably leads to higher accuracy within modeling)?
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Possibly. I have a '73 GE book somewhere in a tub in the garage, with my other books. Can't find it right now, at least within the window of consciousness within the REALLY F***ING HOT garage. Heatwave + Phoenix + Garage is not a recipe for long-term digging around out there....
:D
 
Definitely a fascination

In 1986 when my very first Mesa Boogie finally arrived ...A fully loaded Mark III Simul-Class head and a 2x12 with 2 EV ....I opted for the “American Rock” tones with 4 6L6 power tubes.

I was totally beside myself ...massive sound with tons of tone!!

The outer pair of power tubes are switchable ...meaning I can take the 2 6L6 out and use 2 EL34/6CA7 there for what they deemed as the “British Rock” tones.

Holy smokes! Massive tones as well but with such presence and feel!! .... I’ve not experienced before!!

However, I preferred the overall flavors and tones the 6L6 offered!!

At the time I wished both sounds were available on the fly!!

With all the great tech talk info here...I wonder how Mesa was able to pull it off??....

Btw.....Mesa’s Simul-Class patent that allowed them to somehow have a low wattage Class A amp for it’s sweet flavors somehow integrated with a Class AB amp for higher output was in my view a great move!
 
reclavea said:
Definitely a fascination

In 1986 when my very first Mesa Boogie finally arrived ...A fully loaded Mark III Simul-Class head and a 2x12 with 2 EV ....I opted for the “American Rock” tones with 4 6L6 power tubes.

I was totally beside myself ...massive sound with tons of tone!!

The outer pair of power tubes are switchable ...meaning I can take the 2 6L6 out and use 2 EL34/6CA7 there for what they deemed as the “British Rock” tones.

Holy smokes! Massive tones as well but with such presence and feel!! .... I’ve not experienced before!!

However, I preferred the overall flavors and tones the 6L6 offered!!

At the time I wished both sounds were available on the fly!!

With all the great tech talk info here...I wonder how Mesa was able to pull it off??....

Btw.....Mesa’s Simul-Class patent that allowed them to somehow have a low wattage Class A amp for it’s sweet flavors somehow integrated with a Class AB amp for higher output was in my view a great move!
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They just calculated a bias voltage for the
yyz67 said:
I get it. :fire: Lived in Phoenix until a few years ago. Only option might be early morning which can still be warm.
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Lows in the 90s lately. Maybe if I get up to take a pic of the comet and feel ambitious....
 
I remember buying matched sets of power tubes for my amps in hard and soft style types. The hard being a more sturdy construction with more vacuum and soft being normal construction and less vacuum. You can measure resistance and capacitance all you want but it does not it tell all. The mechanical construction works with the electrical components. More parameters to look at or more tube options?
 
For those who don't hear a difference - it is just possible that you don't notice it for whatever reason.

Use the RTA block or an eq analyzer - that should solve that.
 
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