power tubes: tone related question

[homesick345]

Let's say I have two completely different sets of power tubes (let's assume two sets of 2X6L6GC for a super reverb)

• One set is a vintage RCA set
• the other set a modern JJ or whatever

Let's assume that both set of tubes present all the exact same readings on a professional tube tester.

What - if any - could explain tonal differences between both sets? If ALL electric values are the same?

Could there be any difference??

thanks

 

[DrBGood]

You will probably get scientific answers and placebo answers. I'm curious to see

 

[uriah1]

Are they black plate RCA or gray.
Other than the longevity and durability of tubes built like a tank., my tonal
answer is superb. From a oscillator produced line graph ..it may be subjective.
Quartz is pretty and so is a diamond. A Suzuki motorcyle will get you
there and so will an Indian.

 

[Dacious]

In short - yes there can be difference. If you look at the structure inside the glass you will notice the metal plates have small differences.

While in the same environment with the correct plate voltage and negative grid bias they should be in operable condition they might have individual differences in current draw that change how they respond. Some might need to be biased up more than others even of the same brand.

Inside the distances and gaps between the internal elements are critical to performance.

This can vary tube to tube.

 

[SoK66]

Good question. While I was doing an overhaul update on my '68 Super Reverb I took what had been a NOS set of RCA's out and put in a mid-late 2000's set of GT 6L6GE's. (I discovered I had four new sets of them in my tube stash, all from around 2007-2008.) The GTs were just going to be in there while I was freshening up the amp (electrolytics, a few drifted resistors and a ceramic cap). It sounds so sweet I haven't put the RCA's back in. Granted the "sweetness" may have more to do with the changed out bits, but the GTs are a righteous tube.

 

[JamesAM]

tubes operate at the atomic level - they function by literally bombarding electrons through a control grid and onto an anode plate. Because of the tiny scale of how they operate and the significant effects a small change in materials or orientation could have, I would think it's almost impossible to generalize tube components' specific impact on sound - especially when used in circuit with potentially hundreds of other components. Put it through a scope though and you might get a more objective answer?

It makes logical sense though that the difference in tube materials and/or orientation from brand to brand would make them potentially sound different with statistical significance. I just dont know the specific mechanism of action that would cause it, and I don't really know that it's possible to isolate it, as there are so many variables in tube construction.

 

[Blrfl]

Vacuum tubes are pretty much the poster child for inconsistent manufacturing.

 

[slider313]

Differences in components used: mica or ceramic spacers, support rods and getter wire; their thickness and metallurgical make up, thickness of the glass, material used for the base, etc.

 

[homesick345]

Differences in components used: mica or ceramic spacers, support rods and getter wire; their thickness and metallurgical make up, thickness of the glass, material used for the base, etc.

How could that translate to the OPT & Speaker?

What would the OPT read from the tubes other than electric values?

 

[homesick345]

I am vastly aware of differences in construction, quality & reliability, among tubes........ & how much an old RCA set is hard to beat for stability, reliability, consistency, etc...

YET, again:

How could that "better construction/materials" translate to the OPT & Speaker?

What would the OPT read/get from the tubes other than electric values?

 

[mad dog]

There are definitely tonal differences, but IMO, they don't exist only theoretically, outside of an actual amp circuit.

Example: I had a worn mid 60s Ampeg Gemini II. Had a PT change and switch to 6L6s, which was available as a factory mod. Then switched to a tube rectifier, and I stuck in an Emi Big Ben. I tried several vintage sets of 6L6s in there, including RCA black plates, Sylvania STR 387, Tung Sol 5881s, a pair of 7581A tubes ... all the usual excellent tone subjects. Nothing beat the set of JJ 6L6s I had started with. That amazed me.

I tried more or less the same roster of old and new tubes in other amps. In an Allen Encore head, the RCA blackplates were a big step ahead of everything else. In a tweed bassman, it was the TS 5881 vintage tubes that stayed.

My takeaway is that there's a lot more going on than just the tubes. There is no "better, best" without considering the context.

 

[black_doug]

There are definitely tonal differences, but IMO, they don't exist only theoretically, outside of an actual amp circuit.


. . . My takeaway is that there's a lot more going on than just the tubes. There is no "better, best" without considering the context.

Components used throughout have values that are within a certain tolerance. This will also have an overall effect on tone.

 

[King Fan]

I don't know much about tube testers, but I thought a tube tester only tests a few steady-state electronic variables, and most tube testers don't even test the tube under load. Your Harbor Freight saw has just the same amperage, HP, etc. as your DeWalt? How come the DeWalt cuts so much better -- and yeah, sounds different?

Let's do the testing in reverse; ears first. If your NOS RCA and your JJs sound the same to you, then you're a happy guy -- you can save a lot of money on tubes. And you'll also save all the money you'd've spent on a tube tester.

 

[beyer160]

The RCAs will have a flavorful piquant of almonds, ligonberry and Savoy truffle owing to its artisanal, bespoke origins. The earfeel is exquisite, and will provide a bursting cornocopia of lows, mids, highs, and crunchy smoothness in their crystal lattice to make even the most discerning tubevore quake in orgasmic delight.

The JJs make your guitar louder.

 

[JL_LI]

But the real question is does it matter more than the strings?

 

[schmee]

I hear a difference in some tubes. It's not a big thing though. JJ 6L6's in particular can be clean and almost harsh compared with some. I have them now in an old BF Pro.
I would say the tonal difference is less than the difference in types of strings. That's why I use what's quiet and reliable over what "vintage"

 

[Blrfl]

What would the OPT read from the tubes other than electric values?

I think what you're missing is that while vaccum tubes of the same designation do approximately the same thing, their construction and current condition have an impact on how they behave. Tube testers make very rough measurements of a few characteristics of a very complex system and aren't really capable of capturing those differences. Put the same tubes on a good curve tracer and you'll probably see some differences but, again, not all of them.

Tubes and transistors are a lot like carburetion and fuel injection for running a gas engine. Tubes and carburetors get the job done, but there's so much variance that they rarely get it done exactly the same way (or exactly the right way) every time. That gives them a certain charm but they come up looking pretty ham-fisted from a measurement standpoint. Fuel injection and transistors tend to be a lot more precise in their operation and are often characterized as being sterile.

 

[Milspec]

Consider vintage caps vs modern....some thing. They may have the same electrical values, but the materials make for a different outcome.

I will not say a better outcome, but a different one. MAny find vintage tubes to sound better, but really, they sound better because they sound like what they grew up hearing. To sombody born in the '90's, they probably sound bad.

 

[JamesAM]

I am vastly aware of differences in construction, quality & reliability, among tubes........ & how much an old RCA set is hard to beat for stability, reliability, consistency, etc...

YET, again:

How could that "better construction/materials" translate to the OPT & Speaker?

What would the OPT read/get from the tubes other than electric values?

I really don't think this question is possible to quantitatively answer outside of "this tube tends to sound better to me over this one," for two reasons:

- There are maybe a handful of people left on the planet who engineer vacuum tubes and choose the reason for using specific materials or configurations, and many of the RCA secrets are lost to time due to them being an almost completely obsolete technology

- The sheer number of variables and their contribution to sound within the tube itself, let alone within the more complex circuit of an amp

Like, I don't think it's possible to say something like "the alloy used in RCA's grid has more tungsten than JJ, leading to more even order harmonics and a more complex gain profile" (note, i have no idea what grids are made of, take this as an example of the hypothesis I think you're asking for)

As with literally everything tube amp related, robrob has a great page explaining the different components of tubes. Every part in there will contribute to the amp's sound in one way or another.

How Tubes Work (robrobinette.com)

This is part of the magic of guitar amps: theres an element of ancient mystery in there! embrace it, because this unscientific aspect of gear is what makes it so fun.

 

[VintageSG]

There is a difference. The materials used have changed. Up to, say, 75% of the rated output ( number pulled from ass, wiped clean and given a pep talk ), they'll sound the same. More or less. It's when clipping and compression come into play that subtle differences can be heard by the user, not neccessarily anyone else.
Some of the materials that used to be routinely used have now been effectively banned due to concerns regarding toxicity and/or radioactivity should the valve be compromised. Take the cathode coating as a prime example. Who doesn't want barium and strontium in the house?, just like thorium mantles and uranium glass were replaced because some folk objected on elfin safe-tee grounds. Dang those hippies..

The materials change brings about an operational change.

Try this. Using a single-ended EL84 amp, set it so it is producing 2 Watts clean. Listen to a JJ EL84, a Sovtek EL84 and a Reflektor 6p14p-EV. Not much in it. Now, keeping the pre-amp gain down, to keep things as clean as possible up to the output stage, turn the amp right up. They're now different enough to make out the changes, even though you'd probably be unable to determine which is which. The JJ is safe, the Sovtek is fairly safe, while the Reflektor, being made with materials now on the naughty list, is less safe, should the valve be smashed in a confined space.

Materials make the difference. If material 'A' takes 1mS to effect a change, but material 'B' takes .5 or 2mS, and there are many such changes ( again, turd-coated numbers from a no-no place, no correlation to reality ), these changes may be summed or subbed through the signal path.

Some of these changes bring a valve closer to the original design spec for performance, some move it further away. If a coating has an emissive or absortive value that deviates according to current or temperature, it will sound -slightly- different. -slightly- being key.

It's a rabbit hole. A deep, unlit rabbit hole with gennels and enclaves to distract you. material differences are the main key.

Don't go down the rabbit hole. Plug in, turn on, tune up and play. far more rewarding.