EL84 Tubes: Hard, Medium or Soft?

Hamtone

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I would guess its on the same lines as the groove tube rating? Pure speculation

early, medium, late breakup
 

Deftone

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Sounds reasonable....Thank you.
 

>Photi G<

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I thought it was how they were produced: Hard Vacuum, Medium Vacuum, or Soft Vacuum. That is...how much air was pulled out of the tube during manufacture. Each might yield a different sound. IDK for sure, just guessing.
 

danzego

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I thought it was how they were produced: Hard Vacuum, Medium Vacuum, or Soft Vacuum. That is...how much air was pulled out of the tube during manufacture. Each might yield a different sound. IDK for sure, just guessing.
That's pretty much the deal. :thumb: The more complete the vacuum is, the less easily the tube will break up and the gassier it is, the easier it will break up. Some tubes, in general, are known as harder tubes (like a 6L6), whereas others (like an EL34) are classified as softer....and, obviously even tubes of the same type vary in the same sense.
 

Splattle101

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I don't think this is to do with the vacuum. Air in the tube will lead it to die more quickly.

The 'hardness' in this case would refer to how hard you can drive the tube before it distorts. The harder tube is cleaner. The softer tube has earlier breakup.

I have heard this business about this being caused by the hardness of the vacuum before - I think somebody from Groove Tube might even have said it - but it sends my bullshit meter off the scale. I don't think this is the case at all.

Without knowing for sure, I would reason that the variation in performance would be due to differences in the application of the cathode coating, and minute differences in the spacing between electrodes. But air in the tube would make it glow a violet colour and burn out quite quickly.
 

PINKBITS

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I'd agree with Splatts. They are referring to how quickly the valve will overdrive.
 

Blind Lemon

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It has to do with how much current they draw for a given voltage. More current=cleaner.........hard, med, or soft is marketing. Order the tubes as to how much headroom you want or don't want.
BL

PS If you want killer EL84s do a search for Sgt Overdrive and order some Saratov's from him. Thats what I put in my PeckerHead Rockets.
 

danzego

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Again, it has to do with the vacuum and, more specifically, the pressure of the gas inside of the tube. It's not like information on this is very hard to find. For instance:

Vacuum tube - Wikipedia, the free encyclopedia

Some special function vacuum tubes are filled with low-pressure gas: these are so-called soft tubes as distinct from the hard vacuum type which have the internal gas pressure reduced as far as possible.
 

Splattle101

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They are talking about a different kind of tube. The valves in a guitar amp are not special function, they are plain old garden variety receiving tubes.

The hardness and softness is as Blind Lemon said, a matter of current draw. Have a squizz at this:

How Vacuum Tubes Work

It's a good primer on valves.
 

BrianGT

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I'm absolutely certain it is nothing to do with vaccum.
They don't partially "vaccum" some more than others in production.
It is how easily they do or don't break up and that is all to do with the amount of current they draw.
They vary......so good Tube stores will calibrate them in to groups so that they can be sold as matched pairs.
Soft, medium or hard........or.........low, medium or high headroom.
 

danzego

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They are talking about a different kind of tube. The valves in a guitar amp are not special function, they are plain old garden variety receiving tubes.

The hardness and softness is as Blind Lemon said, a matter of current draw. Have a squizz at this:

How Vacuum Tubes Work

It's a good primer on valves.

And that primer on valves states that the "hardness" of the tube refers to the vacuum. :laugh2:
 

Deftone

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Great link. Thanks, Splat.

I guess we can all agree that the "harder" the tube is the higher the clean headroom?

In other words, "softer" tubes distort at lower volumes?

Or am I totally confused here?
 

Splattle101

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Great link. Thanks, Splat.

I guess we can all agree that the "harder" the tube is the higher the clean headroom?

In other words, "softer" tubes distort at lower volumes?

Or am I totally confused here?
You are correct, Deftone.
 

Deftone

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Is this what Danzego is reffering to? (2nd section from top, blue font)

"Figure 3 (Inside a miniature tube) shows a typical modern vacuum tube. It is a glass bulb with wires passing through its bottom, and connecting to the various electrodes inside. Before the bulb is sealed, a powerful vacuum pump sucks all the air and gases out. This requires special pumps which can make very "hard" vacuums. To make a good tube, the pump must make a vacuum with no more than a millionth of the air pressure at sea level (one microTorr, in official technical jargon). The "harder" the vacuum, the better the tube will work and the longer it will last. Making an extremely hard vacuum in a tube is a lengthy process, so most modern tubes compromise at a level of vacuum that is adequate for the tube's application."
 

Hamtone

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Is this what Danzego is reffering to? (2nd section from top, blue font)

"Figure 3 (Inside a miniature tube) shows a typical modern vacuum tube. It is a glass bulb with wires passing through its bottom, and connecting to the various electrodes inside. Before the bulb is sealed, a powerful vacuum pump sucks all the air and gases out. This requires special pumps which can make very "hard" vacuums. To make a good tube, the pump must make a vacuum with no more than a millionth of the air pressure at sea level (one microTorr, in official technical jargon). The "harder" the vacuum, the better the tube will work and the longer it will last. Making an extremely hard vacuum in a tube is a lengthy process, so most modern tubes compromise at a level of vacuum that is adequate for the tube's application."

Which I would not think you would be able to label
 

danzego

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Great link. Thanks, Splat.

I guess we can all agree that the "harder" the tube is the higher the clean headroom?

In other words, "softer" tubes distort at lower volumes?

Or am I totally confused here?
No, that's the deal. Here's another word on it, from Sweetwater.com:

Glossary: SOFT/HARD VACUUM | Sweetwater.com

SOFT/HARD VACUUM

Terms used to describe the intensity of the vacuous space within a vacuum tube's glass envelope. A hard vacuum denotes a more complete vacuum is created in the tube manufacturing process. Hard vacuum tubes - like the 6L6 and 6550 - have a higher saturation threshold and therefore distort less easily then soft vacuum tubes. Soft vacuum tubes - such as the EL34 or 6CA7 - have a less intense vacuum (sometimes called a gassy vacuum), saturate more easily and therefore break up [distort] more quickly.


btw, the excerpt you posted from that other guy's article is what I was talking about. :)
 

BillB1960

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From what I've been able to tell there are some X-Ray tubes which have a variable vacuum applied to them based on the level of emission and therefore penetration that is desired. I wouldn't guess this applies to guitar amp tubes however. I find it very hard to believe that 'hard', 'medium', 'soft' applies to the amount of vacuum in an output tube which is destined for a guitar amp although I guess anything is possible. I'm thinking it's more likely that the tubes are tested for their plate current and graded & matched accordingly. The higher the plate current the 'hotter' the tube so the sooner it will break up. My guess would be that the higher the current the 'harder' it would be graded.
 

Splattle101

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No, that's the deal. Here's another word on it, from Sweetwater.com:

Glossary: SOFT/HARD VACUUM | Sweetwater.com

SOFT/HARD VACUUM

Terms used to describe the intensity of the vacuous space within a vacuum tube's glass envelope. A hard vacuum denotes a more complete vacuum is created in the tube manufacturing process. Hard vacuum tubes - like the 6L6 and 6550 - have a higher saturation threshold and therefore distort less easily then soft vacuum tubes. Soft vacuum tubes - such as the EL34 or 6CA7 - have a less intense vacuum (sometimes called a gassy vacuum), saturate more easily and therefore break up [distort] more quickly.


btw, the excerpt you posted from that other guy's article is what I was talking about. :)
Jayzus wept, that quote from Sweetwater is just nonsense. No wonder this going around as fact. :rolleyes:

The level of vacuum in the valve will mainly determine its life expectancy. If it's gassy, it'll be short.

The level of distortion is to do with the current draw. It is not to do with the vacuum. It is to do with how much current the anode can take before it is 'saturated'. That is measured in milli Amps (mA), which is charge per second. It is an indirect measure of the number of electrons that need to hit the anode (or 'plate' in American speak) before the anode can carry no more current. Maximum current.

It has nothing to do with vacuum.

Regarding vacuums, a good vacuum is called a hard vacuum. A poor vacuum is a soft vacuum. These are semi-technical terms that have been in use for a century.

The confusion has crept in because of the valve vendors terms 'hard' and 'soft', which refer to distortion ratings. Bear in mind that distortion was NOT a design objective in audiophile equipment, and wasn't a design objective in guitar amps until the late 60s. The Fenders and early Marshalls were meant to be clean. So the use of the words 'hard' and 'soft' to describe the breakup characteristics of valves is a relatively recent thing. Since the 70s at the most.

But these terms refer to the distortion characteristics of the valve. This is dertermined by current draw, as described above. Just because they use the same words - 'hard' and 'soft' - doesn't mean they are talking about the same phenomenon.

The quotes that you've shown us from the Wiki and the other article don't support the argument that this is about vacuum. The Wiki thing was referring to specialist tubes (mercury vapour rectifiers, for example). The other quote merely repeats the usage of the words to describe vacuum, as they've been used for a century or more. But they do not say that a 'hard' tube has a harder vacuum. That's a misunderstanding from sellers like Sweetwater, who can't really be trusted or expected to know what they're talking about.
 


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