How a Vacuum Tube Amplifies

Back to basics
When I went to electronics college we learned all about the transistor amplifier. We had a lot of formulas and most of us in class could do calculations with these formulas and come up with the right answers for the test. But the basic concept of how the transistor actually amplified or even worked was missing. Nobody of my class could really explain how it really worked. They taught us the physics side of it with electrons being attracted from one side to another and then a lot of high level formulas where you inserted values in to calculate the various resistors and voltages to be used to achieve some sort of gain. I thought that there had to be a simple explanation as to how it really worked rather than a lot of formulas and discussions about electrons moving around.

One day I decided to step a sine wave through the amplifying device to see if I could make some sense of it. What happened to all the voltages as my sine wave went in slow motion into the transistor or vacuum tube? I came up with some simple basics that anyone can follow. Funnily enough I have used these basic rules to debug many circuits over the years and explain basic operation to many kit builders. Very knowledgeable electronics people may scoff at these simple rules but if you are starting from scratch like we all were in electronics college, these simple rules will give you a basic understanding of how the amplifier circuit works.


The amplifying device
So above we have a generic device which could be either a tube or a transistor, let’s call it a tube and give it the proper pin names. There are basically three pins and this would be considered a TRIODE like a 300B single ended TRIODE.

Now let’s start with the CATHODE of the tube, this is the most important point on the tube for debugging. If you have a correct voltage on this tube you can be close to guaranteed that your tube is ready for operation. In other words the tube is now like a horse about to take off down the track.


High Tension
Let’s look at some other things in this picture – we have something called HT or High Tension. This is basically the HIGHEST LEVEL DC voltage that we are going to use to run our tube. This is what the power supply will supply to the tube. It sits at this voltage all the time and does not change. At the bottom of the tube you can see GND – this is ground potential or zero volts.


One of the most important facts about this current flow is that the actually current does not change ‘much’ – it’s called a constant current source. If the tube is set up for 2ma to flow through it, then that is a constant – R=V/I, so if the resistance is fixed then the current is fixed.

The Bias
When a tube has been properly BIASED and is working correctly a big current flow will occur from HT to GROUND – think of it as a river flowing in one direction. BIAS means we are going to set up certain voltages and resistors in order that the tube can actually operate, it’s like getting an aquarium ready of a certain size and a certain water temperature such that a fish of a specific size can comfortably live and thrive in that aquarium.

Preparing the Tube

So how do we start preparing a tube so that it can operate correctly and amplify our signal?


Let’s start by adding a resistor in the current flow path. This resistor is called the CATHODE resistor because it sits between the cathode of the tube and GROUND. Most of us know the famous equation R=V/I which stands for Resistance equals Voltage divided by current. I can’t tell you HOW many times I used that formula during electronics college. By using this formula we can calculate how much current we want to have flow through the tube – by putting a resistor in here of a certain value we will control the CURRENT flow in the tube.

I have put a 1K resistor (which equals 1000 ohms) which gives me a cathode voltage of 2V which is in the range of our generic tube and a current flow through the tube of 2 ma which is also within spec of our TUBE. Whether it’s a 300B with a cathode voltage of 70V DC or a 6SH7 with a cathode voltage of 1.5V – every tube has a cathode voltage and an associated current flow. By using your voltmeter you can measure the cathode voltage of any tube. If you were to measure a cathode voltage of 0v you would know for a fact that this tube is not conducting any current and is not operating.


Now by installing an ANODE resistor we can control the voltage drop from the HT to the ANODE of the tube. Our tube spec manual will say that it likes to see no more than say 150v at the ANODE, therefore we would come up with a resistor that would drop 100V ( from 250 to 150) given the amount of current flowing through the tube. In our case it is 2ma, so R = V/I = 100/2ma = 50000 or 50K.

Now we have our two resistors selected along with our HT voltage and cathode resistor and operating current. We are all set – our tube is now operating!

I like to use the analogy of a swimming pool with enough water in it, let’s say 6 feet deep such that a swimmer can now comfortably swim across the pool. The specifications for a 5’10” women to swim in this pool is that we have a minimum of 6” of water in the pool and no more that 8’ of water (this is where the pool overflows).


Now let’s look at what we do when we input an AC or audio signal of a frequency in the audio spectrum e.g. 1Khz into the tube. Well the voltage at the grid is fixed at our tube – (It would typically be.6v higher than the voltage at the cathode) – So we now input a voltage at the GRID.


The Wiggle
Now here is the trick to how the whole thing works – think of us ‘wiggling’ the 2V DC at the grid – we wiggle it between 1.8v and 2.2V – so its a little 0.4v wiggle. What is happening here is the little audio signal that is 0.4v peak to peak and looks like a sine wave is ‘wiggling’ the DC voltage at the GRID. NOW the interesting thing about the way a tube or a transistor is constructed is that the voltage at the GRID is directly linked to the voltage at the cathode. So by wiggling the DC voltage at the GRID we are also wiggling DC voltage by the same amount at the CATHODE – so now we see a 0.4v DC voltage swing at the CATHODE which is mirroring the GRID. BUT we are feeding a bigger constant current flow THROUGH the tube path – see next diagram.


So basically what happens now is that as we adjust the 2V at the cathode by adding 0.2 volts to it we have increased our current flow slightly – this same current flow is now going across the anode resistor but the large resistor at the anode causes a bigger VOLTAGE drop than the 0.2v The drop across the anode resistor now could be 2v, so this is a 10x increase and this would be considered a 10x gain. So what we have is a mirror action where whatever wiggle occurs at the grid gets mirrored to the cathode and then amplified by the bigger voltage drop across the ANODE resistor. So this gives us an idea of how our sine wave is amplified.


So by feeding a constant current across a small resistor (cathode) and a bigger resistor (anode) we are able to reproduce the wiggle we saw at the grid. This wiggle is our audio signal which is actually a very complicated signal made up of many sine waves of all sorts of different amplitudes and frequencies which make up the music we listen to.

In an amplifier output stage we actually don’t have an anode resistor but rather the primary or input of a transformer which would have a resistance of say 1K5 – it looks like a resistor to the tube but it is actually a transformer that then transformers the amplified wiggle to the secondary – it’s all quite ingenius. And this is only the very beginning!

6 Moons Review of ANKits room at TAVES 2014, Toronto

“The next room to catch my attention was organized by ANKits, a supplier of high-end audio products sold in kit (DIY) form based on the Audio Note design philosophy. Born out of Audio Note UK ten years ago, ANKits is today a separate and successful entity. The firm has shipped over 2,000 kits in the last decade according to chief operating officer Smith. Several of those kits contain a certain percentage of Audio Note UK parts, in particular the firm’s legendary capacitors, C-Cores, wires and resistors. No matter the source of the parts, take a look at their quality. Some DIY kits available over the internet cram too many parts per square inch, making for awkward soldering. Not here. You get real full-sized metal cases and intuitive wire paths.”

“This room sounded incredible. I think it offered some of the very best quality per dollar at all of TAVES. The music grabbed a hold of me and would not let go.”

Plucked strings were as lifelike as they were in the very best rooms.
An EL84-based amp was providing all the snap one would expect from such a tube and all the warmth too. As a fan of tubed DACs, I am mightily tempted by the $1,625 DAC 2.1 featuring 6922 tubes. As a former kit builder himself, Smith approached Audio Note president Peter Qvortrup about continuing the kit business when Audio Note was in the process of shutting down their kit division in 2002 to focus more on their high-end finished product line. A good deal of AN (UK) institutional memory and design DNA crossed the Atlantic. Observe the tidy layouts in the photo, the short signal paths, the high-quality transformers, the big Audio Note capacitors and the liberal application of tubes. The circuit boards used are among the thickest I have seen and held. Behold the robust casework holding it all together.


There was nothing DIY about the look. Or about the sound.
Brian Smith says that neither he nor Peter Qvortrup could ever have imagined, back in the early 2000s, the breadth of today’s offerings let alone the commercial success of ANKits. DIY enthusiasts have access to a full range of DACs, preamplifiers, single-ended and push/pull mono blocks, integrated amps, phono stages and speaker kits.

According to Smith, the key to ANKits’ success has been the ongoing evolution of the products. He says he is “always looking for ways to improve the products whether it be the design, the manuals, the cosmetics or better parts per dollar. Better parts could mean components of course but also stainless steel hardware, 3mm aluminium chassis, the best heat sinks money can buy and thick 2oz copper-traced PCBs.” These are things a novice kit builder might not notice at first glance.

Smith says that “being a DIY supplier of high-end kits allows us to make product enhancements at a rapid pace–often ahead of our manuals–as the new tweaks immediately move into the next kit shipped. The products over the last few years are in a very mature state and we are still excited about upcoming releases in 2015.” “Can you be more specific?” I asked. “Well,” he said, “check out the room: brand-new DAC technology, EL84 single-ended monoblocks, a few integrated amps and more!”

Tim Smith
6 Moons

ANKits TAVES show report 2014

ANKits had a great show at TAVES 2014 in Toronto, Canada. With a full hotel room showcasing the new Mentor Pre-amplifier and unreleased EL84 Single Ended Monoblocks the sound was amazing and we have a guest book full of enquiries! ANKits brought a superb 15,000$ system to the show that included:

  • Audio Note Speaker kit 03 Hemp 98db
  • Mentor Line Pre-amplifier – check out the Mentor product page on the website here!
  • DAC4.1
  • EL84 Single Ended MonoBlocks 11w/channel (unreleased)
  • L3 Phono


6 Moons review!

“The ANKits room sounded incredible. I think if offered some of the very best quality per dollar at all of TAVES. The music grabbed a hold of me and would not let go”

Some visitors email feedback!

“Observe the tidy layouts, the short signal paths, the high-quality transformers, the big Audio Note (UK) capacitors, and the liberal application of tubes. The circuit boards used are among the thickest I have seen and held. Behold the robust casework holding it all together. There is nothing DIY about the look. Or about the sound! This room sounded incredible.”

“I recently visited you at the TAVES show and was really quite impressed with the sound in your room. I was particularly interested in the Mentor linestage that you have out now………………….”

“I very much enjoyed your room at TAVES, it was one of the best sounding rooms at the show. Following your room there were few that sounded good. you kinda raised the bar a wee bit…. Haha”

“I know you said the new EL84 amps won’t be out until the new year but I guess I’m just getting impatient seeing as your room is still in the forefront of my thoughts……”


Legend 300B / 2A3 Monoblock Power Amplifier Enhancements!

We have upgraded the chassis to the popular Legend Monoblock Amplifier.

The latest version of the Legend now shipping comes with an upgraded chassis which has been increased in length by around 1.5″ to make the build a little simpler. The chassis is still compact, but now has some additional room for wiring.


A brand new manual has been recently developed and we have the wiring and mechanical sections to view here.


The Legend Monoblock is our ultimate single ended power amplifier in the 3K price range. The large mains and massive choke, hardwired power supply along with hardwired  copper insert plate are oozing with quality –  audio builders and  audiophiles alike will be astonished with a pair of Legends in their system!

The 3 biggest trends in audio in our lifetime!

1. 1960’s – Tubes to Solid State

2. 1980’s – Vinyl to Digital 

3. 2000’s –  R-2R DAC’s to DELTA-SIGMA 

When you look at the above list the first two are quite obvious – it made sense for the mass market of audio consumers and retailers to move from tubes to solid state during the 1960’s – more power , less heat , more reliability etc. etc..  Tubes would move to the smaller boutique audiophile market

Vinyl records started to change over to CD’s in the 1980’s – everyone started unloading their record collections and started re-buying everything on CD! Hey they took up less space -there were no ticks and pops – no stylus replacement or setting up cartridges – for the mass’s it was a great move and vinyl moved over to the audiophile corner

The third one might be a little more difficult to understand because it is not very obvious to the consumer. Back in the 80’s and early 90’s computer horsepower was not what it is today – the internet did not even get started at a consumer level until the mid 90’s with faster and faster computers. Back in the 90’s when digital was becoming stable the chips that were used to convert from digital to analog used resistor ladder circuits – basically real electrical circuits made up of voltages, resistance and currents that actually converted binary numbers to voltages that we listen to  – in other words an actual circuit was used and corresponding analog voltages were generated via a real circuit. This soon became an expensive process to continue and with the explosion of computer based sound in everything from home theater, satellite tv, video camera, car stereos etc, the Delta-Sigma chip was born. Now computer horse power took over the job of converting digital to analog, a computer algorythm read in the binary numbers and through a series of calculations derived what voltage should be in our audio signal and what we should listen to. This was an excellent decision for cheap low cost digital sound for the masses! Once again R-2R DAC technology was moved over to the audiophile corner!

The problem however was that the low end and even many high end DAC manufacturers were also moving to Delta-Sigma processing. What about the high end audiophile with single ended tube amplifiers? For these applications Delta-Sigma will just not cut it. As mentioned Delta-Sigma digital to analog processing is fine for 99% of musical applications that we deal with in every day life! Delta-Sigma will just not cut it for high end audiophile listening!

Resistor Ladder DAC technology is used exclusively in all the Audio Note DAC designs. R-2R Audio Note DAC’s support Redbook 16/44 and 24/96 recordings but no higher. The reason is that you can’t implement resistor ladder dac with higher level resolution due to the resistor ladder implementation – its been proven that the higher level resolution does not bring anything to the table when it comes to digital  audio. Simply increasing the number of bits does not solve the problem of listening to digital music without fatigue –  that’s why you can buy 24/192 and higher dac’s for less than one hundred bucks!

It’s interesting how the audio world in 1960 was extraordinarily advanced while the video industry was very basic when you think of the tv’s in those days – 55 years on music technology had been drastically dumbed down while video technology had made extraordinary leaps!

ANK Audiokits announce Level 5 Series Pre-amplifier

It’s our 10th anniversary year and ANK Audiokits is proud to announce our highest level product offering to date – the Mentor Level 5 Series Pre-amplifier. With this exciting new product and the development of our new Level 5 Series power supply ANK Audiokits is entering the world of ultra high-end audio! Our shunt regulated power supply architecture utilizes dual 5U4G rectifier tubes and dual 4 pole chokes and will allow you to finally realize your investment in a power amplifier & tubes. You will hear high end detail with shocking realism along with incredible dynamics and sensitivity to the incoming audio signal.

Check out our new product page on the website here!

Choosing an audiophile level DAC

Things to be aware of in choosing an Audiophile Level DAC

It’s a complicated world out there in the land of digital audio with cheaper and cheaper solutions coming out on the market with higher and higher sampling rates! Many manufacturers are offering very high priced DAC’s and others have offerings that cost next to nothing! – Some DAC’s come in large rack mount cases – others are part of the USB connector!– There is a lot of confusion out there about sampling rates, dither , jitter, oversampling, digital filters, quantization errors, bit widths, USB, SPDIF, 24/96, 192, 384, SACD……. and where is it all going.

Read on to understand what is really going on in digital Audio. Hopefully this article will help you to make an informed decision when it comes to buying a DAC and  understand more about the current DAC you have. Lets start by discussing some major points first and get into the detail later!


“The actual conversion process from digital to analog is very critical” and this is what is at the heart of any DAC – Now listen closely, there are two major methods of accomplishing this conversion from digital information stored on a computer or a disk – the original method and the one currenly used by Audio Note today along with a few other manufacturer’s is by “hardwiring” the digital numbers through an electrical circuit made up of resistors, voltages & currents and outputting a voltage driven directly from the input – as the digital numbers change at the input of our circuit the output voltage changes. This method is referred to as a Resistor Ladder DAC or R-2R.

Its really beautifully simple and effective:

  • No filters in the digital domain
  • No filters in the audio domain
  • No altering or modifying the signal
  • Just pure conversion

Of course there are complexities in the precision resistors and the finer points of the circuits but bottom line is it’s a direct HARDWIRING of digital numbers to actual output Voltage. For an audiophile level DAC this is correct strategy. END OF STORY.


The second method of performing this critical conversion is through computer horse power – basically the computer hardware reads in the first bit of data and continues to read in bits and analyze via complex mathematical algorithms, digital signal processing , quantization , dither , noise injection & feedback and the computer will determine a voltage that has been carefully computationally arrived at. This is referred to as a DELTA-SIGMA.

You may think this is not a very good process compared to good old fashioned hardwired R-2R, but the truth the computer processing method has many advantages:

  • It is inexpensive compared to its R-2R counterpart & very convenient for many musical applications : Internet radio, Home theater, 5 or 7 channel movies with surround sound, Mp3, iPods, digital video cameras, even SACD uses this method.
  • It allows for great versatility, filtering, sound shaping, room correction etc – incredible flexibility and for 99.5% of the music world DELTA-SIGMA is a great way to go.
  • Its cheap ( Seen the cost of many 24/96 and 24/192 and 384Khz sampling DAC’s) – ( DELTA-SIGMA DAC’s love high resolution formats because its easy to process them compared to R-2R). Its easy to manufacture chips with tons of processing, thus SIGMA DELTA dacs are here to stay!

Even companies like Analog Devices that made a range of R-2R DAC chips in the 90’s now have a complete suite of DELTA-SIGMA chips with tons of features. Basically all home theater gear, CD players, video cameras etc.etc. will use DELTA-SIGMA processing. Virtually all modern DAC’s are DELTA-SIGMA based to handle the 24/192 supposedly high resolution formats.

So why did Manufacturers move away from R-2R chips that they developed in the 90’s? Well basically it is an expensive process to create integrated circuits with laser trimmed precision resistors to correctly implement the R-2R circuit. Its much easier to throw a few million gates at the problem! The Analog Devices AD1865 chip used in the Audio Note DAC’s is the highest bit resolution DAC chip that was made with 18 bits and provides 108db of potential dynamic range. So basically when you put a 24/96 signal through an Audio Note DAC you have a potential dynamic range capability of 108db which is approaching twice the dynamic range ever recorded.

So which is the right DAC for you – R-2R or DELTA-SIGMA? For a true audiophile level DAC we highly recommend R-2R!

If you are truly concerned with the very best of 2 channel audio the R-2R DAC’s will clearly outshine the computer processing DELTA-SIGMA dacs for obvious reasons, If you have a high end audio system such as a Single Ended Tube 300B or 2A3 amp or possibly CLASS A push Pull tube amplification , transformer coupled pre-amplifiers, high efficiency speakers, it’s the only way to go.

Listen to a saxophone with an R-2R DAC and you are going to pick up all the subtle nuances associated with this instrument – the attack , the timbre, the decay, these subtle nuances that immediately allow the brain to identify the instrument are absolutely critical to an audiophile.

To Fellow Audio Enthusiasts!

We are celebrating our 10th anniversary year at ANK Audiokits, and have been able to reflect on the many challenges and exciting times over the last decade. We find ourselves  not only having great discussions about various audio topics with customers but also explaining a lot of things that we have learned over the years such as the difference between:
• EL84 & EL34
• Single Ended vs Class A
• MonoBlocks vs Stereo
• Integrated vs Power

Then there is the digital world and millions more questions. We have been lucky in having access to some of the great audio minds and been able to listen to all our creations over and over again. This blog is a great way to share hot topics and ideas with our customer base. Stay tuned as we start to post . Our first topic will discuss the confusing world of Digital Audio!