Hello all.  I hope this post will help me better understand what VR tubes are doing as implemented in the various Decware amplifiers and how changing them might affect the sound signature of the amplifier.  I know Steve uses these in both the SE84UFO3 monos and SE84UFO25 as well as the Torii's.  

I have been enjoying a Torri MKIV (from forum member Tony) for over a year now paired primarily with a very resolving Zu Union 6 supreme. These loudspeakers are 99 dB-SPL @ 2.8V, 39” [1.0m] efficient. I stream through a Bel Canto E1X and listen to vinyl with a Rega P10/Lyra Etna SL/Sutherland Mini Loco.  All very high resolution capable pieces.

Tony was nice enough to include many different tube combinations with the Torii Mk IV. Several different VR tubes as well.  Specifically, the Sylvania OA3 and Cryotone OB3. At the input side there are Raytheon OC2 and 75C1 tubes.

I have read a lot of posts about these amps and learned a lot from Lon, Will and others who use(d) Toriis. I understand that they are used to cause a specific voltage drop but and are used to provide a clean power supply signal. I still have a couple specific questions about the VR tubes.

1. If the OA3 causes a larger voltage drop than the OB3, what is the electric effect on the output tube?  Does this change the output power? Would a specific VR tube alter a KT66 more than an EL-34 or KT77? What would happen if I put in OD3s?

2. The Torii are push pull amps and the SE84's are single ended.  Is that why a OA3 is required/used with the smaller EL84/6P15 tubes?

I'll stop there but I'm sure I'll have more questions.  

Forgot the last question... As I understand it, Steve uses VRs in series, as filters. And along with changing VRs being nice tuning tools, I think these would be the same reasons for use in any of his amps, and for filtering in pre stages where you can't see or change them easily, single ended or push pull.

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FTR, the 0A3 has the least voltage drop. The drop increase from A to B, C and D.

Let's start with this, the Torii uses the VR tubes differently than the UFO amps. The details kinda go down a rabbit hole of tube amplifier design, but the Torii uses them on the grid of the power tube. You can think of that as the part that "plays" the music. It will effect the sound, not the power. I would encourage you to experiment with the different combinations of VR tubes and power tubes to determine for yourself how they impact your system and what you like.

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The UFO amps use the the VR tubes on the plate of the power tube, and are used primarily because they remove noise in the power for the tubes. Ideally you would do this for every amp, but the the EL34/KT88 etc. type tubes need more power than a VR tube can provide, so they are only available for the UFO type amps with EL84/6P15P tubes.

Hope this helps, more questions welcome.

 

James, I have not looked in my Torii for which pin the power VRs go to, and I find it interesting what you say about Steve's VR use with different tubes, and therefore amps. What I don't get right off is, though different than lowering the plate voltage, within a given plate voltage, I thought lowering the grid voltage would lower the current between the cathode and plate, in turn lowering the output of the the tube.

It sure sounds like that in a Torii when you reduce either the power tube VR voltage, or that of the VR before the inputs.

What am I getting wrong?

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I'm going to tap out here Will, you are getting into operating points and load lines and stuff I had to know once for a class (that I hated) 40+ years ago but don't know any more. This is why amp designers make the big bucks.

I do know you are right, everything else being equal lowering the grid voltage is going to lower the output. But everything is never equal. What Steve says in the manual is lowering the grid voltage will "slightly decrease the gain." Note that gain and power (if used carefully, and I expect Steve would) are two different things. Gain is how much the output voltage, aka volume, changes when you change the input voltage, aka the volume control knob. Power is the ability of the amp to maintain that output voltage into a load without distortion.

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What I can say is lowering the plate voltage on the input tube of my UFO25 with a VR tube also relaxes the sound, in a way that "feels" like less power I don't think it actually is. I think the tube is working at a different operating point and just "sounds different." If it lowered the power you would be able to compensate by increasing the volume, but that just makes the relaxed sound louder, not less relaxed.

This may help?

https://en.wikipedia.org/wiki/Voltage-regulator_tube

Pedantic is appreciated!  I’m a physician and tend to convert electronics to physiology.  Current equals blood flow. Voltage equals blood pressure. Capacitance is vessel compliance…. You get the point.  

Thanks for the reference and reminder what an AC voltage actually means.

Hey Karl. Most of my observations, and assumptions based on them, start from what I perceive from the music, and how that sounds to me. I have always been inclined to follow my perception more than measurements or theory. And to refine those senses and discernement, I have avoided a lot of the, to me limited, though often useful, measurement data and conventional theory, that if taken too seriously, too easily results in absolutist "facts" that do not make sense based on all the complexities we hear.

This does not mean I don't think these tools are not real or useful, in fact right now, I wish I had a scope so that I could measure the power coming out of the tubes we are running VRs to. It is more that I have spent years tuning into changes made, early on with modifying instruments, then system room refinements, and later making more and more cables and doing lots of modification work. There is no doubt for me that progressive practice with mainly the "listening experience" as guide, has honed my perception and discernment, making analysis of the influences from different wires, caps, connectors, resistors, designs, settings... more articulate, including discerning what I hear from the whole with refinements. The other side, measurements in our culture can become a crutch that can limit our perception and discernment... Probably a different fine line for all of us, but also, measurements we have so far simply cannot differentiate much of this vast complex of balances that make our audio experience more or less real.

Still, I really like to find catalysts like this discussion that can cause me to want to read up on the the established views of causes and effects, seeking research information in context making it easier to approach for me.

I started to describe how cathode, grid and plate interact, but then decided to see what the Brave Browser search's AI would say, which is not perfect, but so far very impressive at grabbing info from numerous articles (or whatever) that relate to the question, and answering it in a consolidated way based on the question.


But first, in my experience the voltage going into the amp is notably influential on the the sound, more voltage in, a more powerful and concentrated/dense signal, and less, a more open and complex signal ..not just alike, but not dissimilar from what we hear from changing VRs.  

The natural assumption, adjusting voltages to the amp, adjusts voltages in the amp, changing the sound with these revealing tube designs. This led me to a PSAudio P5 regenerator.


I can't find the receipt but maybe 2009 or so, with my new Torii MKIII, I was having difficulty tuning my system as precisely as I wanted, and finally figured out that this was because the system was always changing sound, from more open and leaner to more consolidated and full. Measuring the voltage as this happened, the power at the receptacle changed, a revelation for me. Though not really very noisy power here (then) the voltage measurement varied over time from something like 119 to 123, and mostly stayed on the higher side. On Steve's suggestion, I put a variac in front of my Audio Brickwall distribution box that fed the amp, and this was interesting, corroborating what I thought I was hearing from increasing and reducing voltage. I preferred it set much lower, opening and relaxing the intensity of all that made the sound... But I did not like the loss of transparency with the variac in the power chain, and did not like how the house voltage still shifted, even though it was manually controllable by the variac at any given time.

So I got a demo PSAudio P5 and found it had transparency issues for me in this system too, but less, and it had voltage regulation. I found then that I preferred maybe 117 or so as I recall, 6 volts less than the peak voltage before, not weakening, but making all aspects of the sound less forced.

First I made a cable for it that I tuned specifically to open, speed up, and clean the sound of the P5 as it related to all beyond. Later, I soldered some connections replacing slip on connecters inside and put in some more transparent receptacles. Then I discovered how phase adjustments on the P5 could alter the density and spaciousness of the sound, and started to really like it. It is still not quite as transparent as my other lightly filtered distributors, but pretty good, and it has other benefits that outweigh.

I check it every so often, but now, many years later, I still end up at 117 and -5 to -7 on the phase. Here, lower phase adjustments reveal more fine detail in space, effecting everything, but easily read by decays, spaciousness, textures...

The other tool I really like, I use because of the way I use Swiss Digital Fuse Boxes (SDFB). If not familiar, they replace fuses by sensing problem like fuses would blow for, but electronically disengaging, in my case allowing hollow silver, and silver/rhodium fuse shaped tubes in the place of fuses. The silver tubes offer more powerful, faster, cleaner, and resolving sound than pretty nice fuses I had...Though most like solid "sluggos," I like the hollows. Similarly to turning up the P5 voltage before modifications, solid "sluggos" of similar quality metal make the sound too forceful and intense for my setup, where the signal unfolds very quickly and easily. Presumably, it is the lower mass of metal with the hollows that put me between fuses and solids, the sound strong, dynamic, and clean, but not overwhelming to me.

Anyway, rather than one SDFB to each piece of gear I am pushing it, using a 5 amp SDFB for my P5, and amp... and one 3 amp SDFB for my DAC, ZRock, Zstage, and CSP3. Leading me to a benefit of the P5 regenerator. You can set up delays for turning on its different receptacles. I have mine set so the P5 comes on first alone, then maybe 10 seconds later, the four front end/pre stages come on, and maybe 15 seconds later, the amp comes on, in theory making the inrush less on the gear, and through the SDFBs.



But back to tubes, below is what I copied from the browser search about grid voltage, and the links below that are presumably what the AI referenced. Pretty new to me, I often reference some of the top articles to corroborate the accuracy. Though general, this sounded pretty real to me. Steve's design choices with series wired VRs and cathode biasing are bound to have some effect, but based on what we hear with VR changes, it is obvious they are changing the tubes that follow, and though this does not go into subtler detail of cause and effect like Steve might, I think it at least basically explains what is happening from changing the grid voltage with VRs:

"does the grid voltage alter the bias of the tubes and what are the effects on tube power"

Grid Voltage and Tube Bias Effects

Yes, the grid voltage directly alters the bias of a vacuum tube, and this change has significant effects on the tube's power output and operation.

The bias of a tube is fundamentally determined by the voltage difference between the control grid and the cathode. A negative grid voltage relative to the cathode is applied to set the operating point, preventing excessive current flow and ensuring the tube operates within its linear range. When the instantaneous grid voltage (the sum of the DC bias and the AC input signal) becomes less negative or even positive relative to the cathode, the tube conducts more current, effectively making the bias "hotter". Conversely, a more negative grid voltage reduces the current, making the bias "colder". This relationship is highly sensitive; a small change in grid voltage can cause a large change in plate current due to the tube's inherent characteristics.

The effect of altering the grid voltage on tube power is direct and critical. As the grid voltage becomes less negative (or more positive), the plate current increases, leading to higher power dissipation in the tube and a corresponding increase in output power. However, if the grid voltage becomes positive with respect to the cathode, the tube draws grid current, which can lead to excessive power dissipation in the grid itself, potentially causing damage or mechanical distortion due to overheating. The maximum power output is limited by the tube's ability to dissipate heat, which depends on its cooling method. In power amplifier stages, particularly in push-pull configurations, accurate matching of tubes and precise adjustment of the control grid bias voltage are essential to ensure both tubes amplify equally and prevent performance issues like distortion. The bias setting also influences the sound; for example, a higher grid bias (colder) can make an amplifier sound more open but with a "sizzly" high end, while a lower bias (hotter) can produce a warmer, more compressed tone.

AI-generated answer. Please verify critical facts.
🌐
tdpri.com
What are the operating limits on the grid to cathode relationship? | Telecaster Guitar Forum
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aikenamps.com
What Is Biasing?
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amfone.net
Grid Bias
🌐
john-a-harper.com
Tubes 201 - How Vacuum Tubes Really Work
🌐
hans-egebo.dk
Vacuum tube biasing methods
🌐
tubes.njunis.net
Grid current, why does it occur? – tubes
🌐
reddit.com
r/AskElectronics on Reddit: Vacuum tubes - why don't electrons "go down" the positive grid?
🌐
sciencedirect.com
Grid Bias - an overview | ScienceDirect Topics
🌐
sweetwater.com
What Is Tube Amp Biasing? How It Works, Why You Should Care - InSync | Sweetwater
🌐
oestex.com
Tubes
🌐
tubes.njunis.net
Grid Leak Bias or Contact Potential Bias. – tubes
🌐
forum.fractalaudio.com
Power Tube Grid Bias | Fractal Aud

As for voltage regulation tubes, I've been fascinated lately with a variant form of 0B2 that have really added a great signature to my amp.

It is not quite as tall as the W forms, nor it is as diminutive as the 75C1 or 90C1. And it has an unshielded body and a clear top so it gives off a vivid orange glow.

I have two US made by Raytheon, one Mullard made in Britain and two made in Holland labeled United Electronics. These share the sort of "texture" I love with the 75C1, but have a slightly more forward, very open sound. I've become addicted to their use. . .

The Raytheon below.

Here is the Mullard (on the right).

They have differing characteristics. I like the United Electronics best as regulation for the driver tubes, and the Mullard best as regulation for the input tube. . .but they are also the ones with the most time on them. Raytheon tends to seem more powerful, pushy. . . Mullard is pretty balanced, United Electronics are warm and with a very endearing smoothness that seems due to high resolution.

All three came from ebay, different vendors. Just have to hunt and peck. . . I will say I have never had a bad tube purchase from ebay in two decades.

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To me this is an excellent description of how grid bias, aka fixed bias works. On of the AI references,

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has an explanation of cathode bias that (finally) makes sense to me. This is how bias in Decware amps works, emphasis added by me:

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How the VR tubes fit into this scheme is a mystery to me, if the grid is held at ground. Perhaps the VR tube is not used for biasing, instead it is used on the music signal feed into the grid? Another thing that just occurred to me is the Torii has 4 power tubes but only 2 VR, so they are split between the push-pull pairs of power tubes. What's up with that? And, FWIW, it seems like Steve has ditched this on the latest Torii MKV, and now the VR tubes are only for the input tubes.

As for the tubes themselves, one of the many reasons I decided to upgrade my UFO amps to UFO25s was the ability to include the VR tubes in the tool box, and they don't disappoint. What really fascinates me is how different tubes with the same rating can affect the sound so much. For signal tubes I guess it sort of makes sense that differences in e.g. cathode chemistry or grid/plate construction can cause tubes that test the same to pass a very compliated signal like music a little bit differently. But VR tubes are soooo simple the scientist in me just scratches his head, and listens and learns.

Sorry that last post took me a while to try to make it least confusing...all this up-side-down stuff these tubes introduce. I hope it makes sense.

I remember that "Oh Jeez" well Kyle. My wife and I lived outside River Falls, WI for several years doing our pottery apprenticeship there, while exploring making our first pottery setup and living in an old farmhouse we rented, wheels, wood kiln, clay making, etc. It did not have plumbing or electricity, and was haunted, so the rent was just $40 for three of us. When we wired and insulated the house, the rent went up to 60!  We really liked hanging out with the old time farmers. "Oh Yeah," those were the days!

CAJames post #4: "Let's start with this, the Torii uses the VR tubes differently than the UFO amps. The details kinda go down a rabbit hole of tube amplifier design, but the Torii uses them on the grid of the power tube. You can think of that as the part that "plays" the music. It will effect the sound, not the power."

Hey James, before going further, can you tell us where you learned that the Torii uses the VR on the grid of the power tube? And also, does this apply to the input tube VRs, the VR's used on the grid??? I am not easily finding this so if you could fill me in, that would be great.

P.S. There is this quote from Steve in the UFO25 development thread:

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Thanks James. One reason I asked was in hopes of finding more specific information about how Steve uses VRs on the the Torii power tube "grid," and however he implements them on the inputs, toward us figuring out how that all works with cathode biasing. Though the whole thing is vague based on my limited knowledge, your thoughts on this part make some sense to me.

Most adjustments from stock in my modification work are pretty straight forward, usually relatively minor changes based on what I have learned from how things sound. So usually the research I do is if I am wanting to do something that seems risky and unknown. Still, I have adjusted cathode, grid, and plate resistors in what I thought were low key enough ways toward getting the sound I wanted without negative effects, and had I thought it was as daunting as it seems now, probably would not have!

Relative to my being a source of your knowledge of the VRs adjusting the grid of the power tubes, not having felt the need, and with my form of dyslexia, as confusing as concepts of cathode/grid/resistors/VR relationships feel now from looking at conventional information, I imagine I would remember my knowing this. But I have never felt like I had enough bandwidth for all I would like to be able to take in and hold sometimes, and a lot of stuff that is not regularly interesting to me can get shuffled into the ethers to make room for current interests! So maybe it was me who told you this

Anyway, one thought relative to the quandary over using VRs to adjust the "grid" voltage, and how that relates to cathode biasing, was... Could it be that the control grid and cathode resistors in Steve's design are set for a milder bias range that he likes with the OA3 on the screen grid as part of that, and that those settings allow enough flexibility to adjust the voltage of the screen grid with VRs? Thinking of the screen as pretty high voltage if done in sort of a standard way, not much below the B+/plate, then the voltage difference, even without resistors to tone the VRs down, going from an OA3 VR75, to OB3 VR90 is only 15V.

However this works, what Steve does is clearly not standard practice, so it is really hard to find direct information with established web references.... and Steve so far is not helping us figure it out... and none of the pics I have of my amp modifications show the tube wiring well enough, caps and wires and resistors covering the tube socket view too much.

I don't really want to go into my MKIV at the moment since I am using it these days, and it is heavy, and my back is sort of blown out. But my MKIII, which also has two sets of VRs, is in a place where I could open it up and see how the VRs are wired if we thought that might help. What do you think?

Hey Will,

I've got some catching up to do.

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I couldn't find the thread last night, but I found it now.

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1747958215/9#9

So you told me the VR tubes are used on the Torii power tubes, which I didn't know, but not explicitly on the grid. I guess I just came to that conclusion based on the process of elimination, and/or Steve's post that I quoted being lodged in my subconscious. Before I responded to Karl's OP I looked up the Torii MK4 manual and found the line about VR tubes changing the grid voltage.

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Maybe. Honestly, anything more complicated than triodes is too hard for me to wrap my brain around and in my head I assumed the tubes in the push-pull amps were strapped to triode. But, it does NOT make sense to have a VR tube in the signal path, for the same reason you DO want it on the B+: it will remove fluctuations. On the B+ that is noise. On the (control) grid it is your music. So, yeah, even though usually when someone says "grid" I think they mean control grid, maybe it is the screen. But I have no clue how different values of screen voltage affect sound/gain/power.

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If only we knew which pin it was .

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That makes sense to me. You say "clean power" but I would think it is as much about flexibility tuning the sound.

I just looked at the datasheet for an EL34 tube and got some new info. It turns out using the tubes as pentodes, push-pull, with cathode bias there should be a 470 ohm screen grid resistor "common to both valves." So it seems perfectly reasonable to have a VR tube split between both tubes if it is attached to pin 4, aka g2, aka the screen grid.

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Here's what I think. There are two different "powers" to keep in mind. One is the instantaneous power of the music to which you are listening "right now," the other is the maximum power the amp is able to deliver to your speakers without distortion.

And, at the risk of being pedantic, let's back up a little bit to how tube amps work, in the big, oversimplified, picture. There are two amplification stages: the input stage amplifies the input voltage,  aka music, from your source, the output stage amplifies the current associated with the voltage. Then the output transformers "transform" the power tube output from high voltage/low current to low voltage/high current to drive the speakers. Speakers respond to a voltage difference across the speaker terminals, the greater the difference the louder the sound. And the greater the voltage difference the more current the amp (i.e. the power tubes) needs to supply to keep the signal from distorting.

As you say,  power = current X voltage, so the power your amp is producing at any time is the current flowing out of the amp X the voltage at which it is flowing. You can define "out of your amp" as either "out of the power tubes into the transformer" or "out of the transformer into the speakers." The current and voltage are (very) different in those cases but the product is (more or less) the same, and corresponds to the volume you hear. And the thing that sets the instantaneous power is the input voltage, determined mostly by the setting of your volume knob. As you turn up the volume, the voltage at the input stage increases, the amount of current sourced from the output tube increases, therefor the output power increases. You can alter the gain, how much or how little a change in the input voltage affects the output power, by changing the the so called operating point of the tube (defined by the relationship of cathode, grid and plate voltages and currents, with no signal present) but in general you will get the same power output from your amp regardless of operating point by setting the volume appropriately. To be double redundantly clear, power out of your amp equals volume out of your speakers.

Then there is the "rated" or maximum power for your amp, 20something watts for your Torii, 2 point something watts for my UFOs. This isn't an issue in my listening life, and doubt it is in yours, but it is the point where output voltage from the amp is so high it can't source enough current to deliver that voltage to the speaker without distortion, aka clipping. This is also determined by the operating point of the tubes, and corresponds to the maximum current that can flow from the cathode to the plate. But, what it is doesn't really matter unless you listen at clipping.


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IMO you are drawing the wrong conclusion. I think your amp "sounding" more or less powerful is because at different operating points the tubes will amplify different frequencies slightly differently. This is like harmonic distortion, and changes the "feeling" of the sound, I'm guessing mostly by how much it emphasizes the mid to low frequencies. I think that is also the reason different tubes, that test the same, can sound very different as well: the differences in the details of the tube construction change the harmonic content of the music, not the power. If the difference was signal power, you could adjust the volume, and therefor the power, to get the same sound as with other VR tubes. But that isn't the case. As you turn up the volume the "more or less powerful sound" just gets louder. It doesn't sound more or less powerful.

Regardless, this has been a very helpful and enjoyable discussion for me even if it has rubbed up against some of the trauma I suffered in circuit theory classes in college.