Tube Rolling: Does it Make a Difference?

[mhardy6647]

 

[watchnerd]

We went to the moon on tubes.

 

[dfuller]

G shock resistance, too, in some cases.

Yes, military tubes were often considerably ruggedized compared to their consumer counterparts. Compare a Bendix 5992 to a consumer grade 6V6GT, for example.

We went to the moon on tubes.

Nah, the Apollos were all resistor-transistor logic in SSI ICs. Radios might have been tube based, I dunno.

 

[watchnerd]

Yes, military tubes were often considerably ruggedized compared to their consumer counterparts. Compare a Bendix 5992 to a consumer grade 6V6GT, for example.


Nah, the Apollos were all resistor-transistor logic in SSI ICs. Radios might have been tube based, I dunno.

Oh, you're right.

Just space then.

Jeff Bezos stuff.

 

[Doodski]

transconductance, cathode current, inter-electrode capacitances

Ima a nooB with tube/valve gear. Is it actually a transconductance curve with all that transformer action, is it linear? The plate reactance that issue is Miller capacitance?

 

[DualTriode]

Ima a nooB with tube/valve gear. Is it actually a transconductance curve with all that transformer action, is it linear? The plate reactance that issue is Miller capacitance?

Here is a 5670 data sheet take a look at page 3 for the transconductance curve.

https://frank.pocnet.net/sheets/093/5/5670.pdf

Thanks DT

 

[dfuller]

Ima a nooB with tube/valve gear. Is it actually a transconductance curve with all that transformer action, is it linear? The plate reactance that issue is Miller capacitance?

Transformer coupled stages are a different story. Capacitor coupled stages (like inside an amplifier before the power tubes) will track the plate curves pretty closely.

 

[pseudoid]

@mhardy6647
Are you sure it was Abraham Lincoln who said that?
Are you sure that it was NOT "William Bruce Cameron"?

 

[Doodski]

Here is a 5670 data sheet take a look at page 3 for the transconductance curve.

https://frank.pocnet.net/sheets/093/5/5670.pdf

Thanks DT

Thanks. Those are transconductance curves. Not exactly sure yet how the graph works yet because I'm not accustomed to thinking in valves and high voltage stuff like these devices. The amplification factor is the range where amplification occurs on the transconductance curve and it's shown in what would be analogous to hFe with a transistor? A gain number?

 

[dfuller]

Thanks. Those are transconductance curves. Not exactly sure yet how the graph works yet because I'm not accustomed to thinking in valves and high voltage stuff like these devices. The amplification factor is the range where amplification occurs on the transconductance curve and it's shown in what would be analogous to hFe with a transistor? A gain number?

Yeah, mu is essentially equivalent to hFe.

A triode is more or less equivalent to how an n-channel JFET works. Plate = Drain, Grid = Gate, Cathode = Source. The curves are a little different - triodes are actually way more linear sans feedback - but the basic mechanics are largely the same.

 

[Doodski]

Yeah, mu is essentially equivalent to hFe.

A triode is more or less equivalent to how an n-channel JFET works. Plate = Drain, Grid = Gate, Cathode = Source. The curves are a little different - triodes are actually way more linear sans feedback - but the basic mechanics are largely the same.

Ogidoki... so the lesser the grid voltage the more linear the transconductance mu curve for this specific valve/tube? But the shorter the range of useful linearity whilst being the straighter of the lines of mu? How does this fit into the grand scheme of valve/tube stuff?

 

[audio2design]

Even when I record my own bass, using my own mics, in my own living room, and play it back in the same room, and do my best to make it sound as close as I can to what I hear in person....

It's never very close to live.

2 channel stereo, itself, is not realistic.

It is very hard to put your ear exactly where a microphone is when playing bass

Musicians are often surprised to find out they don't sound how they think they sound.

But kidding and reality aside, you have lots so many spatial cues (many frequency based), that how could it sound the same?

 

[dfuller]

Ogidoki... so the lesser the grid voltage the more linear the transconductance mu curve for this specific valve/tube? But the shorter the range of useful linearity whilst being the straighter of the lines of mu? How does this fit into the grand scheme of valve/tube stuff?

Okay so some translation is necessary - mu is a product of multiplying the internal resistance (usually termed plate resistance or Rk-a) by the transconductance.

And that depends on the tube. Generally tubes should be biased in the center of their linear operating region, for a class A amplifier stage, so you have the most range on either side for input voltage swing between cutoff (no current flows) and saturation (it can't flow any more current). That depends on the tube you're using, the supply voltage, and so on. For a 12AX7 with a 100k load resistor and a supply voltage of 300 volts, that usually means you want to bias the grid to about -2V with respect to the cathode. You can either do that by injecting DC onto the grid and grounding the cathode, or you can connect a resistor in between the cathode and ground to elevate it above ground, and leave the grid at ground potential.

 

[solderdude]

See what you seem to be missing people is that all tubes even of the same type are substantially different in construction. And they were not designed to sound the same.

Only a few tubes were designed for the analog amplification part. Most tubes are purpose designed. For rolling tubes they need to be within certain parameters to begin with otherwise they won't bias properly.
And yes they are different in construction and for different reasons but work on the same principle.
Audio tubes were all designed to 'sound' the same. Tubes from a similar family, when used correctly' all have very similar frequency response.
It usually is the components around the tube (and the circuit) which determines the 'sound' the device as a whole has.

You should understand that tubes were not made to the same specification, even the same tube types.

I understand. I even design tube hybrids around this knowledge.

And there was no STANDARD for frequency response (not to mention many tubes used in audio amplifiers were not designed for audio) back in the post WW II period that I am aware of. Are you? I've not seen references to 20 hz - 20 khz until like the 1970s.

I am aware of that.. are you aware of the reasons for that ? Are you aware what determined the frequency response ? Do you reckon it was the tubes or the transformers and circuits ?

SO:

would it not be stranger for the tubes to sound alike than it would be for them to sound different?

Would it not depend more on the circuit like topology, feedback and components around it for them to sound different.

You do realize all transistors also measure differently and all other active components also measure differently and maybe purpose designed where the purpose is not audio yet used that way ?

 

[DanielT]

Tubes are angry. So much shit is said about them but here comes their revenge.

Their march into space.

NASA develops speedy vacuum tube prototype for computers in space

Researchers have developed a vacuum tube prototype that is both fast and tough against radiation, making it ideal for computers in space.

www.theverge.com

By the way .... Hifi does not get more fun than you make off it ......
(or far-fetched silly for that matter he he. NASA's tube project though is serious and no nonsense)

 

[PierreV]

View attachment 169756

William Bruce Cameron – Quote Investigator®

quoteinvestigator.com

1963, Informal Sociology, a casual introduction to sociological thinking by William Bruce Cameron, Page 13, Random House, New York. (Google Books snippet view) (Checked on paper: Fifth printing, January 1967; Copyright 1963)

 

[Bob from Florida]

Though I wasn't expecting any particular sonic difference, which likely means it wasn't an expectation bias in particular, that's not the only form of sighted bias. I still could have been imagining the differences.

Also, I'm pretty sure from what I've since that, taken together, tubes and the full amp circuit, I'm likely not getting any more power out of the KT120s vs the 6550s. (I think the amp puts a limit on that, and that the amp would have had to be designed to specifically take advantage of a higher power tube. At least that's what I think I've gleaned from conversations about those tubes).

When you swapped the KT 120's for the 6550's - did you readjust the bias? So, whether you optimized the bias or not - you heard a difference. To verify we could measure a couple of things. First, you could test for output impedance changes - affects damping factor. Being a tube amp we need to be careful - no open circuit voltage measurements! I would try a 100 ohm load and consider that "open circuit" to get the reference voltage at a given driven frequency. Being a tube amp we can short circuit the output with no fear as we lower the load until the output voltage is half the reference voltage. That load resistance is the output impedance at the driving frequency. Best to do sweeps with fancy test gear to plot this by frequency. Another way is to sweep your system with a measurement microphone and plot spl versus frequency. Compare the plots for between output tube plots for measured differences.

If your perceptions are real it should show a measurable difference. Some tube amp OEM's publish specs showing expected output power with different power tubes. KT120's always seem to glean a few extra watts versus 6550/KT88's. Five extra watts is not much loudness wise but might get you a bit more undistorted headroom.

 

[HiZ]

This DIY tube pre amp seems to have been decent with low distortion, or? Tube pre amp with tube ECC88

Index of /Morello/Tube-preamp

faktiskt.io • Visa tråd - GDS-projekt: rörförsteg - LEVERANS!!

It will be used to replace microphone parts, is there a vacuum tube with good specifications for low distortion? The existing vacuum tube is 6AU6.

 

[don'ttrustauthority]

Only a few tubes were designed for the analog amplification part. Most tubes are purpose designed. For rolling tubes they need to be within certain parameters to begin with otherwise they won't bias properly.
And yes they are different in construction and for different reasons but work on the same principle.
Audio tubes were all designed to 'sound' the same. Tubes from a similar family, when used correctly' all have very similar frequency response.
It usually is the components around the tube (and the circuit) which determines the 'sound' the device as a whole has.
....
I am aware of that.. are you aware of the reasons for that ? Are you aware what determined the frequency response ? Do you reckon it was the tubes or the transformers and circuits ?

Would it not depend more on the circuit like topology, feedback and components around it for them to sound different.

You do realize all transistors also measure differently and all other active components also measure differently and maybe purpose designed where the purpose is not audio yet used that way ?

I'm not the one saying that tubes all sound the same. That is what I am responding to.

Tubes are clearly different sounding. I can tell they are because I can hear it with some of them. So if they sound different in the same amplifier then the components around the tube are not affecting the sound of the tube to tube for comparison.

I recently bought a Yggy Gangsta Style from Audiogon and I can't hear a difference between it a BiFrost costing 1/3 the price. You're right, I'm a moron. I should be killed.

I reckon all the components in the chain determine the frequency response. I'm talking about a system that is identical except when changing tubes. Is that difficult for you to comprehend, because I don't see why you'd suggest I'm saying the tubes sound different if I'm listening to different gear ... you seem to be calling me a sub-human piece of shit if you think I am that stupid.

I don't think I'd be able to tell 2 solid state amplifiers apart with confidence. I mean, the class D sounds cleaner than the class AB I have, but it's a much more subtle difference. More bass, more distortion that blurs the image, etc. So there it's probably the amplifiers themselves.

 

[solderdude]

Tubes are clearly different sounding. I can tell they are because I can hear it with some of them.

The effect is design dependent. So the topology and circuit around them determines the 'sound' of the amplifier as a whole.

One can design a tube amplifier with just 1 tube, say a simple triode that has to do all of it. That tube is very flawed in specific ways and alters the signal. One can build an amplifier that has properties that change depending on the inserted tube.
Frequency response, distortion, gain, noise will all be different.
The fact that the gain can differ (even between channels) is often the culprit of someone perceiving the tubes to be different sounding.
Also frequency response and noise levels can be a reason to perceive them to have a different sound.

The problem is to determine if the change in sound you hear is real (and not caused by say the gain or expectation) is that to determine that there really is an audible difference you would have to test this in a scientific way.
This means: having 2 identical amplifiers, The ability to adjust the gain/volume of each channel, using 2 different tubes in each amp, let both amps warm up say. 5mins, and then switch (blind) between the 2 amps. Only then you can truly determine IF the tubes sound different or that it is 'something else' causing the perceived differences.

I am quite certain you have never done that. You can be quite certain I have with a bunch of tubes in 2 equal amps in such a setup because I have a few of those amps (proto's, pre-prod and 1 prod unit) and I can tell you that my non audiophile ears (no idea what Harman level I am ) can't hear differences with quite a few tubes that are well suited but there are also a bunch of tubes that roll-off in the audible band or have a lot of hiss in that circuit and can easily distinguish them.
I don't see that as a having a sound but rather these tubes being faulty or not really usable in that particular design. Of course there are owners who love those tubes (rolled-off or a low added noise level)

You call it 'tubes having a sound' and I call it tubes altering the signal in specific ways determined by the used topology, schematic and tube.

One can also design an amplifier using a bunch of tubes but uses overall feedback. In that case the sound you hear with specific tubes in the simple design will not be there any more. Same tubes being swapped no change in sound. So the same tubes that have a 'sound' in circuit A may not have 'a sound' in circuit B.

It's not the tubes that have 'a sound' it is the circuit and topology combined with specific tubes that can change the response in specific ways (and thus the sound). The fact that you may prefer certain alterations in sound in a certain way is another matter.