Starved Anode – Electron Tube practices

Starved Anode - running triodes at very low voltages

Current Vs Voltage in an amplifier using Starved Anode

The electron tube or radio valve is a voltage controlled device with a very high input impedance and output impedance dependent on configuration of output mode, common grid, common anode or common cathode. What puts it sometimes “off-limits” to the casual experimenter are the high voltages used as well as a heater filament in a directly or indirectly heated device. Although a valve is known to perform best in circuits which are operated within the manufacturer specification, early instruments used battery operated devices to make them portable. Portable radio circuits also used valves which were designed for battery use, the anodes sometimes running as low as 30V. What is not commonly known is that a valve can be run at extremely low voltages in a configuration known as ‘starved anode’. Although used extensively in entry level effects circuits for guitar use they have found their way into the experimenter’s den as front ends for line and headphone amplifiers.

Starved Anode - running triodes at very low voltages
Low voltage +B (Millett’s Hybrid headphone amplifier)

Some reading material on starved anode

So as to not re-invent the wheel the reader and experimenter does have access to very good information on this subject, one of which is listed here: “Triodes at Low Voltages” by Merlin Blencowe. As the author acknowledges, there is not much reading material from the manufacturer regarding starved anode techniques, so by doing his own research and deriving the valve characteristics with a +B of 12V was a logical approach. The article is very well written and demystifies a lot of other stuff for the interested reader which should definitely whet the appetite for anyone interested in pre-amplification.

Radio Museum

Radio Museum: Tubes without operating supply.

There is a lot written about starved anode designs in the forums, most tend to feel that it’s marketing hype but the fact is that certain valves do lend themselves better to running extremely low +B voltages, such as the 12AU7. It certainly is not marketing hype – designs using such low voltages have been around since the first triode tube – what is relevant is that the designs were mostly not used in audio applications. I experimented with circuits in the early 70s which ran at very low voltages but what is significant is that I had access to high voltage transformers and the more common valves – most experimenters these days do not. I am also not an advocate of very low anode voltage circuit designs in high fidelity amplifiers because of the linearity issue but guitar effects are a completely different ball game. Whilst critics condemn the use of starved anode designs the facts speak for themselves – valves do work at very low voltages but how well they work depends on what you want to hear.

Headphone Amplifier using +12V anode on the 12AU7 valve.

 

 

Electronic Marvel – Electron Tubes

Electronic Marvel - high power and radio tubes

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Resilient, Reliable but not eco-friendly – that’s the electronic marvel of the last and current century – the vacuum tube.

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Through the last 100 years the biggest breakthroughs in thermionic tube or valve designs were the multi-electrode devices, from triode, to tetrode to pentode and of course the multi electrode hex-heptodes. All of this was before the second world war.

Electronic Marvel - high power and radio tubes
12AE10 – Credit David Monniaux

Our “modern day” audio equipment using this technology may be dated but just seems so resilient. With the innovation at Bell’s Labs, the invention of the point contact transistor and then later Kilby and Noyce’s integrated circuit it is no wonder that continued research into tube manufacture was deemed as fruitless. Yet tubes have survived, indeed very high powers today are still predominantly controlled by vacuum tube technology – even your domestic microwave oven uses an electron tube, the magnetron, which with ease radiates upwards of a kilowatt peak. With all its simplicity in operation the vacuum tube of the 1950s, 60s and even 70s carried a trademark of craftsmanship and resilience. It is also no wonder that the top lighting manufacturers world wide were also the biggest manufacturers of vacuum tubes. One such manufacturer is Philips, a Dutch company based in Eindhoven that progressed rapidly by hiring some of the brightest minds around at the time. Philips/Mullard tubes are still recognised today as being almost the ultimate in manufacture and are in huge demand amongst audiophiles. Much thanks here of course goes to the foresight of founder members (Gerard and Anton Philips) and scientists in their employ, one of which was the gifted Bernard Tellegen.

The ultimate electronic marvel – the pentode

With the pitfalls of the triode (Lee deForest) and thereafter the tetrode (Walter Schottky) becoming increasingly apparent in tube design and specification, especially in the R.F. field, Bernard Tellegen played a pivotal role in reducing secondary emission and the now well-known tetrode kink of tetrodes by including the suppression grid, to become founder father of the pentode and the pioneer of the EF50, accredited to the team lead by a Professor Jonker. The EF50 was originally designed for television use but found it’s way into radar receivers, an almost indispensable device due to it’s lower operating voltages, footprint and more importantly high gain and cut off frequency. Although it is widely known that Philips held the patent to the pentode tube, it is my opinion that Tellegen’s work is one of the biggest reasons why tube amplifiers still remain so popular today.  (see Wiki EL34 / 6CA7)

Another electronic marvel – superhetrodyne receivers with triode-hexodes

With multiple electrodes in one package manufacturers were able to supply devices which were used as local oscillators/mixers, split triodes, split pentodes and triode/hexodes. In my research patents were granted to  General Electric – triode/hexode, also Heintz and Kaufman.

In our line up one must not forget the cavity magnetron by John Randall and the Klystron by brothers Russel and Surgan Varian, both being extremely valuable devices in the development of microwave radar and of course, modern television and telecommunication microwave transceivers.

 

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If one thinks of the array of semiconductors used to drive a 4 Ohm load to 1kW, the power outputs obtained through paralleling or push pull driven tubes to a few hundred kilowatts was absolutely unbelievable. Modulation at 50%, the power amplifiers of the modulator were equally awesome. All of these transmitters and modulators were water-cooled and had free standing power generation. To date, there are both old and new school engineers calling for tubes to be used in high power transmitters, In high lightning strike areas tubes are almost always preferred because of their resilience.

Some excellent further reading:

 

Vintage amplifier schematics

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Tube amplifier and add ons – Schematics

Electron tubes or radio valves, whichever and whatever way you say it is becoming increasingly popular in the world of sound. Although costing more than their solid state brothers, by keeping to tried and trusted rules, purchasing with your head and not your heart you may be able to put something together which may not break the bank.

Vintage Amplifier Schematics
Sir Ambrose Fleming & Lee deForrest: A bitter Battle

There are many suppliers of surplus military tubes (read: near extinct) on the market. Some companies still have the original tooling and bringing out newly manufactured tubes based on the specifications of popular tubes like the EL84, EL34, ECC82 and ECC83. Perfectly sonic audio matching transformers are being hand-wound.


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For a taste of that tube or valve sound we have listed ten of the most comprehensive websites which list schematics of either well-known amplifiers or tried and trusted designs.


For those whom enjoy reading, here is a real gem, based on the beliefs of the father of the thermionic tube Sir Ambrose Fleming. It should be noted that the father of the triode, a three electrode device (if we see the heater/cathode as one electrode) was Lee deForest.


Go here for links to suppliers of tubes, parts and accessories.


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DIY tube Amp kits, parts and accessories

Tubes, Sockets, Transformers and Kits

For those wanting to build their own tube amplifier or looking for parts to complete a project please find below a listing of dealers and manufacturers of tube amplifiers world-wide. The business listing on Parts-Ring may also list these dealers. This listing may not be exhaustive – let us know via webmaster @ parts-ring.com of any missing supplier.

Note 1: Parts-Ring is not affiliate to any of these companies. In our research the names of these companies came up the most in forums, etc. A company such as Marsamps in South Africa has appeared in Popular Mechanics and is revered as the top tube amplifier manufacturer in the country. If you are listed below please be so kind as to give your company fixed address to we can it listed under the business registration. Thank you.

Note 2: Some companies do not ship world wide. Shipping is hugely based on weight which makes it logical to first check locally for tube amplifier manufacturers. We are particularly interested in Russian, Dutch, Belgium and French suppliers.

Note 3: Do you have access to ex-military job lots? We will advertise your products for free on Parts-Ring.


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Country Name Link  (copy & open link in new tab)
     
U.K. Affordable Valve Company http://www.affordablevalvecompany.com/index.html
U.K. Amp Maker http://www.ampmaker.com
U.S.A. Amplified Parts http://www.amplifiedparts.com
U.S.A. ANK Audio Kits http://www.ankaudiokits.com
U.S.A. Antique Electronic Supply http://www.tubesandmore.com
U.K. Aston Electronics http://www.astonelectronics.co.uk/valve-amp-kits-tube-amp-kits.html
U.K. Audion http://www.audion.co.uk
U.S.A. Boot Hill Amps http://www.boothillamps.com
U.S.A. Bottlehead http://bottlehead.com
U.S.A. Carl’s Electronics http://www.electronickits.com
Malaysia CeriaTone Amplification http://www.ceriatone.com
Germany Das Musikding http://www.musikding.de/guitar-amp-kit-tube-amp-kit-valve-guitar-kit
Hong Kong DIY Hi-Fi Supply http://www.diyhifisupply.com
U.S.A. Doberman Music Products http://www.ax84.com/home.html
Netherlands Dr. Tube http://www.drtube.com
U.S.A. Dynakit Parts http://www.dynakitparts.com
Australia Fred’s Amps http://fredsamplifiers.com.au
U.S.A. GDS Amplification http://gdsamps.com
Canada Grant Fidelity http://shop.grantfidelity.com
U.K. HiFi Collective http://www.hificollective.co.uk
U.S.A. Hoffman Amps http://hoffmanamps.com/index.html
Germany Jacmusic http://www.jacmusic.com
U.S.A. K & K Audio http://www.kandkaudio.com
Canada London Power http://www.londonpower.com
China Mable Audio http://www.mableaudio.com/en
Germany MadAmp http://www.madamp.biz
South Africa Marsamps www.marsamps.co.za
U.S.A. Marsh Amps http://www.marshamps.com
U.S.A. Mission Amps http://www.missionamps.com/kits.shtml
U.S.A. Mojotone http://www.mojotone.com
U.S.A. Mojotone http://www.thevintagesound.com
U.S.A. OddWatt http://www.oddwattaudio.com
U.S.A. TA Weber https://taweber.powweb.com/store/kits.htm
Canada The Tube Store http://www.thetubestore.com/Shop-by-Amp/Guitar-Amp-Tube-Packages
U.S.A. Torres Engineering http://torresengineering.stores.yahoo.net
Canada Trinity Amps http://www.trinityamps.com/Product_Parts.htm
U.S.A. Triode Electronics http://triodeelectronics.com
U.S.A. Tube Depot https://www.tubedepot.com
U.S.A. Tubes 4 Hi-Fi http://www.tubes4hifi.com
Australia Valve Heaven http://www.valveheaven.com
Belgium Velleman Inc. http://www.vellemanusa.com
Canada VK Music http://www.vkmusic.ca
Hong Kong VT4C Studio http://www.vt4c.com
U.S.A. Watts Tube Audio http://www.turretboards.com
U.K. World-Designs http://www.world-designs.co.uk/acatalog/AmpKits.html

These will be added to the business listing in due course.

Go here for Tube – schematics


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Tube Transformers – Output, Filament and Power

Tube Transformers - through eBay

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Tube Transformers – Why you may stick to solid state.

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Many more DIYers are building thermionic tube amplifiers now than ten years back, possibly through hype or possibly nostalgia. They certainly have their place and in one area where they seem to be getting mass appeal are pre-amplifiers, headphone amplifiers and low power audio use in bi-amping. My own experience suggests that solid state is superior for bass reproduction where upwards of hundreds of watts are required to drive sometimes very inefficient bass bins. I do not believe that heavy sounding bass requires a tube amplifier although if you have the money then why not go whole hog and build a 2 x 100W tube amplifier. For a whole lot less, a 15W push pull stereo amplifier and 2 x 100W transistor amplifier will give you all the fidelity you need for bi-amping purposes. Some things for the novice to remember however is not just based on budget constraints – a 6W tube amplifier is going to cost you more than a 100W transistor amplifier. What are the implications?

Tube Transformers - through eBay
Tube Transformers – purchasing through eBay

Unless you are buying the entire kit from a renowned manufacturer which must include chassis, transformers, potentiometers and tubes etc remember that in a lot of cases what you read is based on nostalgia. Thermionic tubes do sound different just as you will gather that certain transistors sound better than others in a specific application. After handing over your hard earned cash remember that the heart of the beast is the audio or output transformer. A poor quality output transformer may discourage you from future projects due to poor frequency response, distortion or low power. Have you done a comparison between a fully fledged tube amplifier i.e. from front end to output, and a hybrid – tube preamplifier and solid state output stage. This dispenses with the output transformer which for most design engineers is the pitfall. (*see note below). If you are still keen then some ‘hi-fi’ die hards prefer to build their own output transformers – it is not difficult but very time-consuming. Good quality transformers use interleaved windings – i.e. packed primary, secondary, primary etc. The lower the primary Z (impedance) the more tubes you will need to parallel (as in transistors feeding two Ohm loads). Datasheets will give you the transformer impedance required otherwise the supplier will know.

(*Note: Certain vintage enthusiasts believe that the output tranny actually makes the audio more musical, in other words, better not worse. A very good output transformer is worth it’s weight in gold).

Tube amplifier design: Stick to Tagboard

The best tube amplifiers are not necessarily built on PCB – they are point to point which will require tagboard. Although I come from the marine industry which used a lot of tube gear still in the 80s plus PCB usage, these were designed and built for extreme weather conditions. Wires did still corrode and drop off. Modern wiring with the dreaded ROHS soldering techniques is not compulsory. In fact it’s a waste of time. Stick to tried and tested techniques.


 

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Output Transformers – Counterfeit and poor quality

Output transformers can be purchased on eBay. Check reseller credentials and don’t say you haven’t been warned – counterfeit is rife. Quality output transformers are expensive. Stick to known brands of tube – there are some very good Chinese tubes on the market but I note that the ‘h-fi’ technologists still veer towards the Russian tubes. Better still, buy locally from someone whom can assist. Tubes do not usually come with a return policy – what you buy you keep. We don’t need to explain the rationale around this. Likewise tube transformers.

Mains transformers – fortunately here there’s many ways to skin a cat. I prefer EI transformers (laminated) in linear supplies to switched mode. This is a matter of choice. Machine wound toroidals have become popular as the pricing has decreased but in many countries they are harder to get than the old laminated variety – shipping can cost you whatever you win on an import. Reverse connecting transformers – connecting secondary to primary is one way to get 220V a.c. output although it costs you space. For experimental setups this is often a solution. Otherwise, if you are into designing with SMPS, use 220/110V -> 12V transformer, rectify, filter and feed into a home brewed switcher. I find this the cheapest solution. 500VA transformers are cheap to come by. (I have used UPS transformers which come at the most economical price = free). Many of them are 14V or 28V. I am advocating this because most of us are wary of designing switchers to run off +350V mains. Tube circuits do not draw huge amounts of current which allows thinner copper wire to be used which is easier to wind. If you are into looking at SMPS design, a good starting (and ending) point is from my personal favourite, Rod Elliott:  http://sound.westhost.com/project89.htm – this project can easily be modified to get the high tension and heater supplies for moderate power circuits. More on heater supplies below. +EHT or +B is often derived from voltage doublers or triplers for low current supplies. This is ideal for a pre-amplifier.

Tube amplifiers use dangerous voltages so do not attempt a build or repair without following the proper safety guidelines – in all cases this means switch off, discharge and test. Rod Elliott’s SMPS may have a low input voltage but current draw will be very high, easy enough to cause severe burns if you are not careful.

Another circuit, designed for ham use, is that found here: http://w5jgv.com/hv-ps1/  – this power supply is not suitable for the newcomer.There will be a lot more questions than answers – stick to the one above for experimentation because the input side is low voltage.

Tube Transformers – Heater / filament voltages

Modern technology has given us the advantage of cheap low voltage regulators with exceptional current handling capability. Tube heaters draw masses of current and using transformers like that used in UPS, lend themselves well for heater voltage control through DC regulation. Using a 7805 regulator with the common terminal lifted by 1.4V (using two silicon diodes in series, forward biased) will elevate the output voltage to about 6.4V which is more than adequate for a 6.3Vheater supply. However, +5V DC should not hinder tube performance that much, in fact it will enhance tube life by running at lower than optimal. It is not advised to go below this voltage – this reduces thermionic emission to the extent where the tube will no longer operate as designed. It will not damage the tube!


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Heater filaments can be coupled in series. Stick to the linear regulation, it is cheap and will offer a huge benefit: Over voltage will not only cause a short lifespan, it may kill the tube. Tubes are expensive.

OTL or Output Transformerless

The gungho of all audio. With the output transformer out of the picture you may save hundreds of $$$ but be careful of the pitfalls. Firstly, besides what the hype tells you they are often more expensive than amplifiers with output transformers. They run several tubes in parallel. The circuitry is highly tuned – they do not like impedances south of their rated, possibly 4 Ohms. Read http://davidberning.com/products/zh230 for a great review.

Bottom line is that if you cannot afford the price of the amplifier you won’t be able to afford the loudspeakers. Although they may be for the high end technophile audio guru, you will need the program material and you will need the proper auditorium. I have heard OTL and SETs and would be hard pressed to tell you that you are getting bang for your buck. They are for the extreme audio enthusiasts out there with very fat wallets.

In conclusion…

My own experiences with tubes, whether it be radar, sonar, high powered SSB all proved one thing: Tubes are very resilient. Running any tube exceeding rated voltages is not a good thing. Although CRT rejuvinators may supply excessive voltage to the heater, they were never that successful. A low emission device needs to be trashed properly (not put into the bin). In most cases tubes cannot be repaired although I have used a capacitor to discharge through an inter-grid shot which cleared the problem. (CRT). Tubes make phenomenal voltage amplifiers yet can be the only solution in high energy circuits. In fact, in many circuits today only thermionic tubes can be used. They may look different but they still work the same.

Tube transformers may still cost an arm and a leg but hopefully this article may assist you in finding cheaper alternatives.

An Eye on Technology – for Optometrists

Hello

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The Sun was designed by a Dermatologist – the Tablet by an Optometrist

Now that the World Cup is on us again, satellite and cable TV sales must be quadrupling which hopefully will see an increase in internet bandwidth worldwide – if you aren’t watching this on your tablet in real time. Frankly I am skeptical about all this small screen nonsense. Years back we were told that those poor youngsters in Singapore had all become myopic because they stared into computer screens the entire day without a little bit of eyeball exercise. Truth this is. In fact things have now become a problem world-wide. We eat in front of the PC, we sleep in front of the PC and we exercise in front of the PC (gaming). Optometrists and general practitioners are making a mint – the only ones that can afford to go to a real gym.

An Eye on Technology - it's all in the mind
Pure Technology – Great Sounding Tablet

The Galaxy Pad S is going to sell big time. Believed to be in a class of it’s own, I have no doubt this is going to be an all time best seller. The problem is, not that long ago we were told that you had to have a big screen to see everything bigger and better. Now I believe you can buy the 8″ (for the cheapskates) and the 10″, for the ultimate in viewing pleasure. What’s the difference between a 10″ and a 50″ in any event besides just screen size? Font size.

Is this the ultimate oxymoron: Playing your tablet through a tube amplifier?

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Tube specifications – Mho and Mu

Tube Specifications - Valve or tube tester

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Thermionic Tube Specifications – from Mu to Miller

Tube Specifications - Valve or tube tester
Sylvania Tube Tester – Flickr Sandstein

Going through the millions of audio equipment ads posted on eBay I’m surprised that China or Russia don’t start building new tube tooling equipment – it’s become quite evident that there is just no rival to the sound of vacuum tubes. From highly musical, ambient, warm, vibrant there is just no getting away from it, hype is in full flight. I tend to agree that solid state designs can sound clinical but when one thinks that a pre-amplifier can be built to a far higher spec than any tube amplifier, which will last longer and cost less then we need to really assess our priorities.

Tube specifications for triode
Tubes – Triode

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Tube Specifications – Russian or Chinese?

This article is not around whether a tube is better than a FET or bipolar transistor on the audio front but rather some of the difficulties posed in their design. There is a large following of Russian manufactured tubes yet the Chinese are also ‘apparently’ bringing out some very good quality tubes. When I read of owners having to change their tubes every one to two years, including pre-amp tubes, is this based on tests conducted or listening pleasure? A tube does not have an infinite life span, does not like to be knocked about and won’t last if it is run outside (over) it’s specification but is still a remarkably resilient device. Just like a transistor there is a safe operating area – my own experience is that a tube will handle overloading better than semiconductors, testament to the many protection circuits around semiconductors to prevent over-current, allow faster switching and protect from back EMF. Of course we could apply this to tubes as well, a load disconnected from a tube audio amplifier is a bad thing, excessive cathode current reduces emission faster than you can say ‘boo to a goose’ and the dreaded insect lying across socket pins causing premature failure – think roach across control and screen grid path. No, tubes can be made to last if they are used within spec. We did not change very expensive transmitter tubes every 12 months – they had very sophisticated safety mechanisms built around them. In fact think what will happen if a transmitter output stage was coupled to a mismatched antenna – this always happens when you are near the coast, caused by salt, sea-air and is even worse when you are at sea.

Tube Specifications - Pentode
Tube – Pentode

Tube Specifications – Bias C, B, AB, A, Mho, Mu and Rp

To bias a semiconductor to either be on or off can be done simply, possibly by the drive circuitry as in the case of switching supplies – in class C, the NPN base is held negative by a few volts, in class B, the onset of current draw, the NPN would have a voltage close to switch on and AB and A, the voltage will be higher in the positive region in relation to the emitter. So what about a tube? It is exactly the same – the control grid is usually biased negative in relation to the cathode. This is the same with triodes, tetrodes and pentodes. When we talk about Hfe in a transistor we talk about the small signal current gain of the device. When we talk about Mu in a tube, we talk about voltage gain of the device. The other term often used is Mho, the transconductance of the tube. Another term often used is Rp or plate resistance. Just as voltage, current and resistance are all inter-related, so are Mho, Mu and Rp. I always found it easier to move from tube designs to transistor designs – there are a lot of parallels but tube circuits are nearly always easier to understand. At least that is how I was taught, from tube to semiconductor. One thing that is not that apparent though is that Tubes have many criteria which affect their gain.

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So we have Mu, Mho and Rp. Another important criteria is the inter-grid capacitance, called the Miller Effect, predominant in the triode.

Mu – the voltage gain of the tube

By applying a fixed voltage to the control grid of a tube and measuring the current through the anode as the anode voltage is increased or reduced and then comparing it to the tube with fixed anode voltage and measuring the current through the anode as the control grid voltage is increased or decreased will show us that a smaller voltage variation at the control grid produces a much higher current variation than the higher voltage variation settings at the anode. This is because the control grid is situated much closer to the cathode than the anode. With a given load resistance (at the anode) a 1V swing on the control grid can produce a 20V swing at the anode. The closer a control grid is placed to the cathode the smaller the variation required to produce a vary large variation in cathode or anode current and hence voltage swing at the anode (or plate). Another way to put it would be that the anode voltage needs to be increased much more at fixed grid voltage to get a rated cathode or anode current than a voltage increase at the grid at fixed anode voltage.

Tube Specifications – Rp of Plate Resistance (Note that anode/English = plate/USA)

Tube Specifications - Beam Tetrode
Tube – Beam Tetrode

Let us now add some figures – let us hypothetically speaking finding that a 50V increase at the anode, fixed bias voltage of -5V at the control grid produces a current of 10mA at the cathode. (our anode and cathode currents are taken to be the same so Ia = 10mA). A 2V increase at grid or bias setting of -3V produces the same current at the cathode. This indicates a voltage gain of 50/2 or 25. However, the anode has an internal resistance – calculated by Ohm’s law to be a change in or Delta Rp (plate resistance) = Delta Ep (plate voltage) / Delta (plate current) = 50V/0.01 = 5kOhm.

Then, as mentioned previously, we have the Mho or transconductance of the tube, the ability to transfer electrons from cathode to anode. The easier the control grid can control this flow, the better.

Transconductance (Gm) in Mho(s)

Whilst resistance opposes current flow and measured in Ohms, Transconductance relates to the ease of current flow.

Transconductance is merely the voltage gain (mu) of the tube divided by the plate resistance (Pr). In this case, 25/5000 or 0.005 Mho. (this can be given as milli, micro as well). The higher the gain and the lower the plate resistance the easier electrons move from cathode to anode (plate).

The Miller Effect

Inter-electrode or grid capacitance is something we have all heard about from degrading bandwidth to the common practice of adding a neutralising circuit to prevent self oscillation. Just what is the Miller Affect?

In particular the triode thermionic tube is affected by anode to control grid capacitance, the inherent capacitance multiplied by the gain of the device +1.  As the control grid of a tube reflects a very high input impedance the input signal has to charge/discharge this capacitance sinked or sourced through the previous stage resistance. This creates a bandwidth filter. This capacitance can also create a positive feedback loop where the tube could enter into self-oscillation. This is not only inherent in tube amplifiers, especially triodes but also bipolar and FET designs. There are numerous ways to counteract some of the nasty side effects of this capacitance, lowering stage gain, reducing load resistance the of previous stage (plate load), running in common grid (or gate or base) configuration, applying negative feedback etc The tetrode tube was in may engineer’s book a step in the right direction – a second grid was located between anode and control grid minimising the effect of the capacitance (by acting as a screen 🙂 )

Brief word on the tetrode.

The tetrode, which used a screen grid (or accelerator grid) caused other complications one of which was the emission of secondary electrons which bounced off the anode. A suppressor circuit – another grid was then positioned between screen and anode which usually sat at ground potential or was connected directly to the cathode. This was called the pentode, a five electrode device. Pentodes were very popular for high gain, low noise and variable mu used in AGC circuits.

Tube testers

One couldn’t write an article like this without covering tube testers – most vintage gear enthusiasts have either purchased their own (expensive) or did their own research and built one. There are some pretty good DIY projects out there, see below.

A tube tester must have a means to change heater filament voltage, anode or plate voltage, screen grid voltage, ac insertion and of course has a multitude of sockets to test different tube types. We can measure voltage gain, leakage, noise, transconductance, Rp and a multitude of other tests. Modern technology also helps us to build far more sophisticated testers than our forefathers with variable plate/anode supplies, testing the tube in different modes, signal injection and of course, using a computer interface we can program the tester to apply the spec voltages to a specific tube by only typing in the number of the tube. This will set bias, anode voltages and even apply a signal with scope out connectors.Talking about hybrid technology.

To get to the point I do not own or have built one. Looking at the many testers out there I doubt whether it would take a miracle to make one although I have my eyes on an Electronamic.Having said that, about twenty years ago I purchased a CRT tester which cost one tenth of what I see floating around on eBay. Most testers have limited +V and only use a good/bad visual indicator

See Steve’s Tube Pages also Repairing Valve/Tube Equipment

In conclusion keeping to tube specifications by the manufacturer is a critical part to good design. Cutting corners, bad wiring, instability, poor ventilation and no regard to human safety are all bad starting points. Tubes can last a long time – just stick to basic rules.

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Mr.Valve

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admin 2014-06-03 17:21:12
admin

Company/Business Mr.Valve
Website http://www.mrvalve.co.za
Business Type Reseller
Category/Genre Electronics – Thermionic Tubes – Valves
Posted By
admin

Core Business Reseller Thermionic Tubes – Sockets – Transformers
Address 1 *See Website for details
Address 2
Suburb Wonderboom
Town/City Pretoria
Region Gauteng
Country South Africa
Zip/Postal Code 2000
Telephone 082 889 0802
Details/Additional

Mr Valve …..
is a home based company that specialize in –

Hard to find valves and brands such as Philips, Mullard, General Electric, National, etc.
“Modern” tubes like, Electro Harmonix, JJ, etc.
Hammond Transformers
Porcelain, micalex and belton sockets
Capacitors: Mica, etc

All of the valves sold, new or NOS, are tested for emissions and defects with a AVO 163 Valve Tester.

All shipping is done via Fastway Couriers or the Post Office Speed Services. We also do international shipping via the South African Post Office.

We supply over 3000 different vacuum tube types, transformers, capacitors and sockets. Our inventory of vacuum tubes and radio tubes are all NOS / NIB and new production and are able to satisfy most tube needs.

If we haven’t got what you need, we will try and find it!


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Asian Motorcycles – Who is doing what?

Asian Motorcycles - four for the price of one

Asian Motorcycles and does China make Honda clones

[google-translator]

There has been a lot of negative media regarding startups globally selling cheap Asian motorcycles and closing their doors either once the owner has made enough money or worse, none whatsoever. The failure rate of these imports was possibly a big culprit but one cannot get around the fact that many of these dealers were and still are unscrupulous.

Asian Motorcycles - four for the price of one
Asian Motorcycles – Bangkok – Photo credit Khaosaming

What makes these motorcycles popular are firstly the price and then secondly, they make quite good looking bikes. The latest bikes are far more reliable if we look at the trend over the last five years. The pricing has stayed the same. What makes them different then?

Asian motorcycles and Burger eaters – power to weight ratio

Looking through forums I came across one where a potential biker wanted to purchase something as his ‘first bike’. The question was whether it should be Jap or Chinese? For a person only wanting a runabout, not wanting to clock up kilometers – possibly just for shopping, going to school or college the Chinese product would more than suffice. Taking it off road or on a long distance cruise may not be a good thing. When we build cheaply the first thing that gets trimmed is the metal. So you may have a flashy dash and a nice looking bike but what are the limitations of load – that means you and possibly a passenger. Most Asians are lighter than their western brethren. The power to weight ratio is better and the steel may not be quite as strong as the Honda. Having said that though we need to realise that Chinese bikes are getting better as export standards are forced to rise. Will we now see more dealers opening their doors, or less?

TIG, Stick and low grade steel

I for one think it is imperative that the buyer knows the carbon steel makeup of these imports. What about the welds. Lots of bad press about. I would not go dune hopping on a Loncin, possibly most cheap imported Asian motorcycles. There is a lot of information about regarding the engines of these imports as well, mostly based around Honda tooling. Yes, I know the old Honda small capacity machines had the same looking engines. Are they as strong though – are parts cheap? Can we even get the plastics and whatever fittings you may need as easily as you purchased the bike? I don’t know – I keep this article unbiased because I know of many school kids that have endless pleasure out of riding their bikes. A common complaint is that the parts fall off. I note no spring washers or Loctite.What we forget though is that now we have many more bikes on the road and a lot more cheap imports. This may not be realistic comparison. People hop on and ride. A motorcycle has to be inspected every time you ride – not just once per month. Regular maintenance keeps a bike reliable.

Many years ago manufacturers took their plants to China – it was just cheaper to produce because overheads were lower (read: salaries). At the same time failure rates increased. One particular ‘manufacturer’ of monitors had more failures in their professional series than their entry level units. That’s a thing of the past – the Chinese got their act together and their electronic equipment, especially multi-national has improved somewhat. Their automobiles and motorcycles are going the same route. For the parent out there take this into consideration – but always put safety first. There is nothing like a free lunch. Chinese motorcycles cost a 1/4 of the price of Japanese two-wheelers and this should tell you something. Japanese products also use stronger motors and motors which deliver more power for a given capacity. Chinese motorcycles are also a lot more around using less fuel. It would if the power is much lower.

Here are the rules. Buy a Chinese bike, quad or scooter and check all nuts and bolts. All motorcycles vibrate and all motorcycles if not maintained properly fall to pieces. Change the tyre for a known good brand as soon as you have the cash. Change the oil every 2000 km or stick religiously to the owner’s service manual. These motorcycle engines run at many more RPM than an automobile at a given speed, run hotter and of course, using mineral oil which breaks down far quicker than synthetics. Don’t just put synthetic oil in because you heard it’s better – read the manual. Most motorcycles use a wet sump – use the best oil you can afford.  If your manual says you can do wheelies (which they don’t) then you have a dry sump. If your bike has a wet sump you will be in for quite a few surprises – one being that your engine may not be getting the lubrication it needs while you impress your chums and girlfriend. Just a few seconds of metal against metal is enough to damage your engine. Have you ever thought about the part when your front wheel has to touch the ground again. Even the strongest motorcycles have a knack for breaking front shocks when doing the ‘landing bit’. Just don’t do it.

A good quality build costs money. Chinese motorcycles are getting better in both reliability and performance. Stay clear of good 2nd hand deals, some are shot even at 10 000Km. As far as the cheap Asian motorcycles go, for the runabout, for schoolkids and starter bikers, they are real gems. But like all gems they need to be washed and polished.

 

Micro Tubes – Thermionic Tube Semiconductors

Micro Tube - another major innovation?

Micro Tubes – Another gadget to add to our Audio

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It was just when we thought we had heard it all when I read an article in the Gizmag covering vacuum channel transistors (May 2012). Are they really a hybrid semiconductor valve? I thought it may have been an April’s fool joke but apparently not. A company in South Korea (with NASA) are developing the best of both worlds – transistors with a vacuum channel.  With a 150 nanometer device the thermal heating process used in vacuum tube technology will be almost negligible.

Micro Tubes - another major innovation?
Micro Tube or FEVA – Under Investigation

What intrigues me is that because vacuum tubes have seemed to have gained in popularity over the last decade why the technology experts, especially our semiconductor manufacturers have not spent more R&D on the tried and trusted radio valve (English) or Vacuum Tube (USA)? Now they can, I suppose.

The quirks of valves – the advantages of micro tubes

Both technologies have their quirks, both have their advantages and disadvantages. Nano sizes mean small power – thermionic tubes are great at releasing huge amounts of energy with great waste. Nano Tubes will not be able to do this but will have the advantages in audio, if the audio gurus permit. I doubt it though – part of the great sound may be a placebo effect – watching the tube heaters glow. Feel the heat and enjoy the awesome sound.

Much has been written about thermionic tubes, even on these pages but why really manufacture a device which will use a fairly low voltage when our pundits of tube audio has claimed that the higher voltages is where the tube gets a lot of it’s unique qualities from, one of course being that ‘great’ sound.

Although we have three categories of audiophiles; bipolar, FET and tubes I’m still an old school believer – a good Sennheiser and amplifier will knock the socks off any quad engineered amplifier no matter the topology. Thundering bass is in a different category – then I want the original sound to be like the live performance and not through some image correction i.e. parametric equalisation and DSP. Multitudes of loudspeakers, tri-amped to perfection – that’s my idea of good quality. I’m also not a great believer in subwoofers and 4″ side speakers to give the mids and highs in a stereoscopic image. The 901s were really great I thought until I read all the biased reviews. Nothing worse than having  cheap arsed speakers outperform the best only because they were set up improperly.

Comparing Micro Tubes to JFETS and NE5534A

From a financial point of view I doubt the nano tubes are going to come out cheap, at least not in their infancy. When FETs came out (actually before the point contact device) they only started to really hit the shelves in the late 60s and early seventies and all audio buffs purchased these for their pre-amps.  With FET written all over it I find it hard to then believe that manufacturers now bring out preamplifiers with only bipolars in all stages. If you don’t believe me. look at the NE5532 and NE5534 IC specs.

It’s all hype – we run out of things to say. All valve (sorry… tube) hype has been around the distortion aspects. Yet when I studied electronics the object was to reproduce the recording (or program material) without any distortion. Has this now changed? Has a distortion free great dynamic range audio amplifier become a thing of the past?

I doubt it. Buy any good class AB amplifier rated at 200W RMS per channel and run it at 1/2 volume. Tube or transistor. For guitar use, who knows – my preference is a tube amplifier.

Micro Tubes – the Finality

Maybe there will be some good coming out of this without us starting to making praising sounds before it’s even off the drawing board. It will still surely be a voltage operating device. Still sounds like an April’s Fools joke to me. Roll over Ambrose.

[Note that the image is tongue in cheek – a FEVA, Field Effect Valve Amplifier. But yes, there is scientific research being done in vacuum channel semiconductor research as in micro tubes. Watch this space! – Ed ]