wonderingape
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What about the dirty gain and dirty volume on the Orange Rocker 30? Is it preamp distortion or power tube saturation?
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Early Marshalls are single channel clean amps?
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What about the dirty gain and dirty volume on the Orange Rocker 30? Is it preamp distortion or power tube saturation?
No doubt, the power amp section has to be working hard to get the grind on my JTM 45.
But when it does, nothing else sounds like that.
Nothing else.
Mystic38
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Well, its pretty hard to discriminate so i can't say for certain whether the power tubes saturate on the Dirty channel.. I "assume" they do when volume is at near max as the texture of the sound changes..i just can't be sure.. but at this point its really, really loud..
guzzis3
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I did read the whole statement:
as far as I know pure 100% power tube "distortion" isn't real and preamp tubes, phase inverter, etc. are necessary to produce overdriven sounds.
I don't know what YOU mean by overdriven. Distortion is an engineering term, it means output deviation from the input signal. Technically that can mean anything. If you run a 60's marshal flat out the output from the output valves will be different from the input. Saying that isn't real is absurd. If you want to argue that the distortion across that stage is being somehow driven by the phase inverter or the output trans or speakers build a test circuit with just an output valve, put a dead clean sign wave in at a high level and look at what comes out.
Now to be clear the specific sound a JTM produces is a function of every component. You can for example change it by changing the power supply section. People reckon they can hear a difference between 50 hz and 60 hz supplies.
Triode harmonic distortion sounds completely different to pentode. You just have to try one of those amps that power cut by cutting elements. This is why people build attenuators, so they can run the output stage flat out without blowing the walls out. If it wasn't true everyone would have jumped on the valvestate type amps when they came out in the late 70's. Clean SS output stage you can dial up the fizz at any volume, but at the time no one thought a valvestate or the many similar amps sounded any good. They were 1/3 the price of a full valve head. There were also a couple of SS preamp valve output amps. I think music man did one but I could be wrong.
Anyway...
Sho enuff, I had one of the hybrid Music Man amps way back when, LOUD.
If you weren't careful give yourself hearing damage! They didn't do it for me, only my opinion of course.
Give me some EL-34's, KT-66's, even 6L6's working hard, that's were the tone is for me.
Call it overdrive, distortion, those are just terms, o.p. needs to play a few, then he'll know.
wonderingape
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"If you want to argue that the distortion across that stage is being somehow driven by the phase inverter or the output trans or speakers build a test circuit with just an output valve, put a dead clean sign wave in at a high level and look at what comes out."
Do you have any audio example of that? Can't find it anywhere. What are the other components other than the power tubes on the circuit? Are you sure the only component there are the power tubes?
There are many examples on the Internet where they compared different power tubes with each other. The only way for them to hear the distortion coming from the power tubes is when they maxed out the clean channel volume with every other knobs at zero (if you're using typical amps such as Class A/B) or when they maxed out the loudness on single ended amps such as the Class A unless if they got attenuators. The only difference I heard is the EL34 have less headroom while others have more headroom (especially in single channel amps), while characteristics such as mid-boosted (more upper-mids) or mid-scooped (less upper-mids or less midrange) mainly come from the preamp circuit, tone stack and speakers.
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wonderingape
Active Member
There are many examples of that on the Internet where they compared different power tubes with each other. The only difference I heard is the EL34 have less headroom while others have more headroom (especially in single channel amps), while characteristics such as mid-boosted (more upper-mids) or mid-scooped (less upper-mids or less midrange) mainly come from the preamp circuit, tone stack and speakers.
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Kinda matches my un-scientific research as well.
My JTM most definitely had more breakup with the EL34's, the KT's don't breakup as much. But imo, they have more tonal "depth"?
pleximaster
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wonderingape
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Sorry, what do you mean by tonal "depth"?
wonderingape
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That's my thought too. Early Marshalls, when their loudness are maxed up, are not clean amps.
Just my subjective opinion.
I think the KT's have more detail, that's just to my damaged ears.
Also know that I think I would be perfectly happy if I never made the substitution. I generally put rolling tubes towards the bottom third on my list of improving/ changing tone.
To my ears it's the different circuits that make the biggest difference. Meaning different amp brands/ models.
pleximaster
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I have build a replica of the Number One Amp at the Marshall museum for a member here on an old Marshall chassis with original old parts and transformers It was suprisingly gainy!!! I ended playing Drop D tuning!!! Haha!
I am making one replica for my self on a new chassis and it will be interesting if it also is as gainy as the first replica. I think there is a thread about it here on the forum.
plexi
guzzis3
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I'm not suggesting you build an amp I'm suggesting you do an experiment. Build a power supply and apply appropriate voltages to each pentode element. Apply a suitable sine wave to the input and the output to an oscilloscope. Increase the input until the valve starts distorting. ALL valves distort if you apply a big enough input.
Regarding different output valves, yes they react differently. The first thing you need to consider is what voltages are applied to each element. For example for an EL34 look at this datasheet
https://frank.pocnet.net/sheets/129/e/EL34.pdf
In class A you can apply 250 or 300V, actually you can go outside those ranges but this will do. At those 2 voltages you are going to get both different amounts of headroom and different frequency response/balance of harmonics when they go into clipping. So the same valve can "sound" different in different circuits, even if both are class A or both AB1.
So then you put in a different but similar valve, and maybe it can use the same voltages, but because (eg) your KT66 is physically built differently to your EL34 even in the same circuit it will sound different. Different level to start clipping, different frequency response. Just like swapping a speaker.
Once you understand all that you start fiddling with preamps, which are the same story. Nearly everyone uses 12A?7s. The Xs are most common, high gain typically quoted about 100x if I remember correctly. So now lets leave everything else as is and use some 12ax7s with different construction. It will change the sound. Pop in a 12AU7 you will get more clean headroom. Change the voltages and you will get something different again.
60's amps generally have very little clipping in the preamp stage, but because of the high gain of the 12ax7 the signal into the pentodes is more than they can handle without clipping. You have probably already lost the top of your sine wave as it exits the splitter but the signal is so big the pentode can't pass it through without distorting it more.
And now it gets complicated. You get all sorts of interactions between transformers passives etc so now at full tilt your 1987 or 59 (or JTM) at full tilt is kinda organic the circuit ringing to different input frequencies, and the speakers are going nuts making sharp violent movements in the air as well as saturating. THAT is the sound. Everything plays a part, although how big is variable.
So now you've got your master volume amp with an extra 12ax7 in the preamp. You roll off the master to the level you are comfortable with and crank the preamp into clipping. You are no longer at 110db the speakers are coping and your pentodes are hardly distorting at all. Even if the rest of the circuit is as similar as possible to your plexi the sound is completely different.
wonderingape
Active Member
I tried to find frequency response graphs of EL34 and other power tubes online but most of them are frequency response graphs of preamp tubes. In the link you've shared with me, it didn't show any frequency response graphs that include sound pressure level and frequency.
So where do the characteristics such as more upper-mids, mid-scooped, cutting through the mix, etc. majorly come from? Is it from the preamp circuit, tone stack, etc.? According to the picture below, it is mainly from the preamp section.
wonderingape
Active Member
The power tube distortion produced by maxed out cranked early Marshalls are low gain mild overdrive with buzzy characteristics by today's standards. As an individual who played mostly hi-gain harsh distortion, I think power tube distortion sounds are suitable for country rock, blues, 60s-70s rock, etc.
guzzis3
Well-Known Member
You won't find frequency response charts for output valves. Depends on a million things but especially output transformers which are never linear.
The capacitors in the preamp do filter. In fact if you want to make a fender sound more marshal or vice versa that's where you would start. The output valves won't make the amp "brighter" or "darker" but when they go into harmonic distortion you will get different levels of each harmonic from different valves. The best way to understand the effect is to listen to a single ended class A like the old X84 circuits with self bias and mid point voltages so you can swap output valves without changing anything else. Use the classic as it has "vintage" ie lower preamp gain. Run it flat out into say an el34 then a 6l6 then kt66 and you will get different sounds. KT88 and 6550 probably won't distort very much because they can handle a lot bigger input before they are overdriven. Actually that's a point. Stick 6550s in a 60s marshall and it will clean right up. The preamp and splitter have not changed, so where did all that distortion go ? The 6550's aren't distorting because the amplitude of the signal out of the phase splitter is big enough to overload an EL34 but not enough to overload a more rugged valve like the KT88 and 6550.
Actually I should check the data sheets because I'm assuming that from memory...
But then leave say an el34 in and swap out the output transformer for very different ones and you'll hear a difference there also.
Swap out caps in the preamp. Use a preamp with no tone controls, only volume, or 1 tone knob.
You will have heard a tweed fender champ running full tilt. That's output valve distortion. The preamp is low gain, relatively, very little clipping going into the 6V6.
Obviously class As distort a lot more than AB1, but it demonstrates the point. The trouble with AB1 is you have bigger volume to manage and a lot less distortion. So it's harder to see things, and they are more complicated so it's harder to isolate things.
The capacitors in the preamp do filter. In fact if you want to make a fender sound more marshal or vice versa that's where you would start. The output valves won't make the amp "brighter" or "darker" but when they go into harmonic distortion you will get different levels of each harmonic from different valves. The best way to understand the effect is to listen to a single ended class A like the old X84 circuits with self bias and mid point voltages so you can swap output valves without changing anything else. Use the classic as it has "vintage" ie lower preamp gain. Run it flat out into say an el34 then a 6l6 then kt66 and you will get different sounds. KT88 and 6550 probably won't distort very much because they can handle a lot bigger input before they are overdriven. Actually that's a point. Stick 6550s in a 60s marshall and it will clean right up. The preamp and splitter have not changed, so where did all that distortion go ? The 6550's aren't distorting because the amplitude of the signal out of the phase splitter is big enough to overload an EL34 but not enough to overload a more rugged valve like the KT88 and 6550.
Actually I should check the data sheets because I'm assuming that from memory...
But then leave say an el34 in and swap out the output transformer for very different ones and you'll hear a difference there also.
Swap out caps in the preamp. Use a preamp with no tone controls, only volume, or 1 tone knob.
You will have heard a tweed fender champ running full tilt. That's output valve distortion. The preamp is low gain, relatively, very little clipping going into the 6V6.
Obviously class As distort a lot more than AB1, but it demonstrates the point. The trouble with AB1 is you have bigger volume to manage and a lot less distortion. So it's harder to see things, and they are more complicated so it's harder to isolate things.
