Luckylm

“Slot Machine” Cathode poisoning prevention routine Programmable 16 milions colors LED tube lighting Neon colon indicators blinking at 1 Hz Tubes are driven in high frequency dynamical indication and provide service for many years All settings are stored in non-volatile memory First tube can be disabled if hours lower than 10 (optional). Any day now @@cubeberg I am now adding software features requested by users. There were few requests for effects that will prevent cathode poisoning, so I will add two effects, slot machine and blanking. Slot machine will basically scroll all numbers for a few seconds every so often.

Intro:
After 22 years of being interested in DIY electronics, I finally decided to build what everyone shoud once build - a Nixie Clock. What the nixies are I describe in more detail in this article.
Clock functions:
Of course, the clock displays the time. Including seconds, because without moving secondswith figures jumping to different depths of the nixie, it is simply not the proper nixie clock.It also shows the date and day of week. It can count leap years and automatically switch to daylight saving time (DST) and back.There is also an alarm clock with single time alarm, weekdays alarm or every day alarm. I also implemented software correction of crystal andoperating hours counter, which is very helpful for monitoring of nixie lifetime. At regular intervals,the slot machine effect (number flipping) is done to prevent cathode poisoning. You can also manually turn on a permanent slot machine for nixie regenerating.As a display I used six IN-12B nixies (character height 18 mm) and as dots I used neon lapms INS-1 designed for DC current operation.
Circuit:
The clock has a display made up of six IN-12B nixies. You can also use IN-12A with no modification. They differ only by the absence ofdecimal point, which is not used here. Nixies are controlled by so called mains duplex. It's similar to the two-step multiplexwhere one half wave of mains illuminates one group of digits and the other half wave illuminates the other group. In this case the display is divided intoeven and odd positions. The advantage of this circuit is that it, compared to static drive, it decreases the number of nixie drivers (74141) from six to three.Compared to the conventional multiplex there are also several advantages. It is not necessary to actively switch the anodes (two HV transistors for every anode). It also does not require as large pulse current to achievedesired brightness, compared to six step multiplex.Classic multiplex is also problematic because of the high rectangular waveform voltage thatcauses a dim glow of inactive digits (ghosting) because of capacitive currents.In a duplex such a problem does not occur because it works with a sinusoidal voltage,rather than rectangular. You also don't have to care about smooth supply voltage, typical of classical multiplex. There are absolutely no capacitors charged to dangerous voltages.The separators are two colons formed by two pairs of neon glow lamps INS-1. They are divided into two pairs connected in series.One consists of upper dots, the second one of bottom dots. This allows you use the bottom dots as dots for date. Both groups of glow lamps are also combined into a duplex,so that they can all be driven by a single HV transistor (T2).
As a control circuit for my nixie clock I chose Atmel AVR ATmega8A (ATmega8L). It provides all functions required for clock. PD3 pin (INT1) is used forsynchronization of duplex via the transistor T1. If the duplex is reversed (ones and tens are swapped), reverse the primary or secondary ofauxiliary transformer TR1. The transformer TR1 (230V / 9V 1.5VA) is used as a supply for logic, but also to sense the half-cycles.5V stabilized voltage is traditionally provided by IO5 (7805) with a small heatsink. To avoid resetting the clock during power outages, they are not lacking abattery backup. It has a voltage of 4.5V (or 3V, 3.6V or 3.7V). I used three AA cells. A much smaller battery would be enough, becauseconsumption during backup is only about 9uA. During battery operation the nixies are of course not lit and so onlyIO1 is operated, not the power hungry 74141. Their self consumption is, according to the catalog, up to 32 mA (I measured 24 mA).Reversed current from the battery into the 74141 drivers and into the 7805 is prevented by Schottky diode D1. The diode D2 prevents unwanted battery chargingduring mains operation.
Piezo beeper Rep1 provides audible signal (alarm). It can be replaced with an induction speaker with about 1uF capacitor in series.Alarm works even when on battery power. The nixie clock is set using the TL1 and TL2 buttons.Pin PD3 (INT1) is used to synchronize the duplex and to detect whether the mains voltage is present. If there isno change in the level for 250ms, the clock switches to battery operation. Outputs of IO1 leading to the 74141 drivers and T2 are set to log 0.Nixie clock is powered from the mains without isolation. Mains voltage of 220 - 240V is about the most appropriate voltage to power the nixies.Operation without isolating transfomator is possible if the clock is sealed in a suitable safe box and no live part are notexternally accessible. The backup battery must be closed and inaccessible from outside (do not use housing for the battery with a door).The buttons must be rated for 250Vac, because it's not just a about contact-contact voltage, but also about contact-human voltage.Nixies are obviously not exposed, they are safely placed under a transparent cover. Construction with exposed nixies is in my opinion not onlydangerous (even in case of power supply isolated from mains), but also quite prone to mechanical nixie damage and ultimately great anachronism(I do not know of any device from the times of normal use of nixies, which had nixies uncovered!). It is of course possibleto construct the nixie clock with isolation transformer (or with a 100-120V / 220-240V transformer for the 100-120V countries). Nixie clock without mains isolation transformer obviously can not be connected to the programming interface.The MCU programming can be done outside of the clock or using the backup battery.
Nixie tube current is chosen as low as possible to extend their lifetime. Some datasheets tell current range of 2 - 3.5 mA and some2.5 - 3 mA. Minimum is therefore around 2 - 2.5 mA. When the current is to low, it can cause partial glow - only a part of the cathodeis lit. When operating a nixie with a pulsing current, the peak current must exceed the minimum required value.Resistors R1 - R6 define the nixie current. Resistor R9 is used to fine tune the current and it can be deleted.Voltage drop of IN-12B nixie is about 130V and the peak voltage of 230V mains is 325V, so at the resistor therefore is 195V peak.The resistors are chosen so that the peak current slightly exceeded the minimum operating current. R = U_{R peak.} (195V) / I_min. (2-2.5mA).If the current was not enough to display all digits correctly, you can reduce resistance values.I chose a peak current of approximately 2.3 mA (average current is about 0.5 mA). It turned out that it is enough to display digits correctlyand also to achieve good readability even in daylight.
Program:
The program for the nixie clock is available for download below in the HEX file (upload directly into the microcontroller) or as source codein assembler for possible modifications. The printscreen below shows the microcontroller configuration bits setting in both AVRISP and PonyProg.The clock is controlled by a low frequency crystal (32 768 Hz), which enables low power consumption when running on battery.MCU is clocked at 4MHz from the internal RC oscillator. AVR goes into sleep mode Idle when inactive during mains operation.When battery powered, it uses Power Save mode, enabling very low power consumption. CPU clock isoff in this condition and only asynchronous timer/counter2 is running. The Nixie clock has Operating hours counter. To avoid loss of data (24bit) while disconnectedfrom both mains and battery, the data are stored in EEPROM and updated 8x per hour. To avoid early EEPROM wear (guaranteed lifetime of eachByte is 100 000 writes) wear leveling is used. The lowest byte storage is rotated between 96 different bytesin EEPROM. For higher two bytes it is not needed because the update only occurs on low byte overflow, which is 256x less often.100 000 writes of a particular byte won't therefore occur before 137 years of continuous operation! EEPROM also holds compensation byte of the crystal.Date and time display cycle repeats every 7 seconds. The number 7 was chosen because it is relatively prime with the numbers 10 and 60,and thus there is no uneven wear of nixie cathodes of seconds when displaying the time. Time is displayed for 5 seconds and date for only 2 seconds,because the time is more volatile and therefore more friendly for nixies.
How to set and use the clock:
The clock is controlled by TL1 and TL2 buttons.
• 1. Time/date display
The clock has two basic modes of display. The first one shows only the time in the form 'HH:MM:SS' (Hours : Minutes : Seconds).Second mode alternately displays the time and date with a period of 7 seconds. Time is always displayed for 5 seconds and date for 2 seconds.Date is displayed in the form 'DD.MM.0W' (Day.Month.Weekday). Weekday is displayed using its number (01 = Monday ... 07 = Sunday)as there's no other way to display weekday on a nixie.Between these two modes you can switch by pressing TL1. In both modes digits are rotated (slot machine) for 1.25 seconds every 49 seconds.
• 2. Alarm clock
The nixie clock is equipped with an alarm. Button TL2 gradually switching between displaying the time, date-time and four-step alarm settings:Alarm hours, alarm tens of minutes, alarm minutes and alarm mode. The setting is done usingTL1 button. Alarm modes are: 0 - disabled, 1 - once, 5 - five working weekdays, 7 - every day.Alarm setting is indicated by alternately flashing dots. Alarm beeping can be stopped by any of the buttons.
• 3. Setting the clock
By long pressing of TL2 you get into the process of setting the time. You set hours, then tens of minutes, minutes, seconds, year,day, month, day of the week and finally the automatic DST (daylight saving time) shift (111111 = on, 000000 = off).The setting is done using TL1, switching between the steps using TL2. After four minutes of inactivity, the clockautomatically returns from settings to the time + date display (this protects nixies from static display).
• 4. Automatic DST
If the automatic DST is enabled, the move to summer time takes place on the last Sunday in March. 1:59:59 is followed by 3:00:00.Move to winter time takes place on the last Sunday in October. 2:59:59 is followed by 2:00:00.(According to the rules valid in almost all European countries including the Czech Republic and Slovakia since 1996)
• 5. Special functions
Long pressing of TL1 get you into special features. The first one is nixie test in whichall nixies run a chain of numbers from 0 to 9. It can also be used for nixie maintenance (against cathodes poisoning).Another press of TL2 will take you to another special feature, which is the compensation of the crystal. If the clock is not accurate,you can adjust it in the range of -75 to +75 ppm with 3ppm (3 millionths) steps. Use TL1 button to set the value.Negative values ​​are displayed on the left, positive on the right (eg. -12 ppm displays as '12 00 00' and + 75ppm as '00 00 75').After pressing TL2 you get to the last special feature, which is the operating hours counter.It displays total nixie operation time (in hours). The following press TL2 longer takes you back to the time display.Operating hours counter can be reset by a jumper wire connected at DP1 long press of both TL1 and TL2simultaneously. The dots will flash quickly and the counter is reset to 000000. Resetting is recommended only when you change nixies.Under normal circumstances it is recommended not to connect the DP1 jumper.
Long term operation experience:
20. 8. 2015 - first 1000h of operation. No failure, no signs of nixie wear.
31. 1. 2016 - 2000 h of operation. No failure, no signs of nixie wear.

Cathode poisoning prevention – the clock can periodically run a cathode poisoning prevention routine, called “slot machine effect”. This helps to keep all digits of all tubes in good condition. Otherwise, the unused digits could stop working properly. Rotary knob – for offline users, there is a rotary knob on the back of the board.

The program for free download:
Source code in assembler (ASM)
Compiled HEX file (2 900 Bytes)
How to write the program into the AVR is described here.

Schematic of Nixie clock with Atmel AVR ATmega8A / ATmega8L and IN-12B nixies.(Click to enlarge)
Configuration bits setting in PonyProg.
(Hexadecimal values are Low Fuse: E3, High Fuse: D1.)
Configuration bits setting in AVRISP.

Completed nixie clock

Nixie clock during construction

IN-12B (ИН-12Б) soviet nixies from 1987 - 1990.
Testing the IN-12B.
Oval sockets for IN-12B. It is probably PL31a-p (ПЛ31а-п) or SK-136. The are made in 1983.
Comparing nixies at a pulsing current (single diode rectifier, no capacitor) at average 0.3mA and at DC 0.3mA.With a pulsing current the glow discharge is much better distributed throughout the cathode compared to DC current, although the average current value is the same.
INS-1 soviet neon lamps taken from a vintage box.
Making the control board.
Making holes for nixie sockets.
Making the board with sockets.
First light.
Board with ATmega8A, 3x MH 74141 and other parts.
Almost completed nixie clock, only the box is missing.
This animation shows 50x slower how the duplex works.
Nixie current on a scope.

Slot Machine Cathode Poisoning Prevention Routine

Box to build the nixie clock into.
Selecting a transformer from drawer stock.
This happens when the nixie current is to low. Only part on digits is lit.
Starting to put the clock into the box.
Backup battery. Much smaller battery would be enough :).
Video - almost completed, only the box is missing.
Added: 27. 5. 2015
home

In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. The heating element is usually an electrical filament heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating. There are two types of hot cathode. In a directly heated cathode, the filament is the cathode and emits the electrons. In an indirectly heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.

From the 1920s to the 1960s, a wide variety of electronic devices used hot-cathode vacuum tubes. Today, hot cathodes are used as the source of electrons in fluorescent lamps, vacuum tubes, and the electron guns used in cathode ray tubes and laboratory equipment such as electron microscopes.

Description[edit]

A cathode electrode in a vacuum tube or other vacuum system is a metal surface which emits electrons into the evacuated space of the tube. Since the negatively charged electrons are attracted to the positive nuclei of the metal atoms, they normally stay inside the metal and require energy to leave it.^[1] This energy is called the work function of the metal.^[1] In a hot cathode, the cathode surface is induced to emit electrons by heating it with a filament, a thin wire of refractory metal like tungsten with current flowing through it.^[1][2] The cathode is heated to a temperature that causes electrons to be 'boiled off' of its surface into the evacuated space in the tube, a process called thermionic emission.^[1]

There are two types of hot cathodes:^[1]

Directly heated cathode

In this type, the filament itself is the cathode and emits the electrons directly. Directly heated cathodes were used in the first vacuum tubes. Today, they are used in fluorescent tubes and most high-power transmitting vacuum tubes.

Indirectly heated cathode

In this type, the filament is not the cathode but rather heats a separate cathode consisting of a sheet metal cylinder surrounding the filament, and the cylinder emits electrons. Indirectly heated cathodes are used in most low power vacuum tubes. For example, in most vacuum tubes the cathode is a nickel tube, coated with metal oxides. It is heated by a tungsten filament inside it, and the heat from the filament causes the outside surface of the oxide coating to emit electrons.^[2] The filament of an indirectly heated cathode is usually called the heater.

The main reason for using an indirectly heated cathode is to isolate the rest of the vacuum tube from the electric potential across the filament, allowing vacuum tubes to use alternating current to heat the filament. In a tube in which the filament itself is the cathode, the alternating electric field from the filament surface would affect the movement of the electrons and introduce hum into the tube output. It also allows the filaments in all the tubes in an electronic device to be tied together and supplied from the same current source, even though the cathodes they heat may be at different potentials.

To improve electron emission, cathodes are usually treated with chemicals, compounds of metals with a low work function. These form a metal layer on the surface which emits more electrons. Treated cathodes require less surface area, lower temperatures and less power to supply the same cathode current. The untreated thoriated tungsten filaments used in early vacuum tubes (called 'bright emitters') had to be heated to 2500 °F (1400 °C), white-hot, to produce sufficient thermionic emission for use, while modern coated cathodes produce far more electrons at a given temperature, so they only have to be heated to 800–1100 °F (425–600 °C).^[1][3]

Types[edit]

Oxide-coated cathodes[edit]

The most common type of indirectly heated cathode is the oxide-coated cathode, in which the nickel cathode surface has a coating of alkaline earth metal oxide to increase emission. One of the earliest materials used for this was barium oxide; it forms a monatomic layer of barium with an extremely low work function. More modern formulations utilize a mixture of barium oxide, strontium oxide and calcium oxide. Another standard formulation is barium oxide, calcium oxide, and aluminium oxide in a 5:3:2 ratio. Thorium oxide is used as well. Oxide-coated cathodes operate at about 800-1000 °C, orange-hot. They are used in most small glass vacuum tubes, but are rarely used in high-power tubes because the coating is degraded by positive ions that bombard the cathode, accelerated by the high voltage on the tube.^[4]

For manufacturing convenience, the oxide-coated cathodes are usually coated with carbonates, which are then converted to oxides by heating. The activation may be achieved by microwave heating, direct electric current heating, or electron bombardment while the tube is on the exhausting machine, until the production of gases ceases. The purity of cathode materials is crucial for tube lifetime.^[5] The Ba content significantly increases on the surface layers of oxide cathodes down to several tens of nanometers in depth, after the cathode activation process.^[6] The lifetime of oxide cathodes can be evaluated with a stretched exponential function.^[7] The survivability of electron emission sources is significantly improved by high doping of high‐speed activator.^[8]

Barium oxide reacts with traces of silicon in the underlying metal, forming barium silicate (Ba₂SiO₄) layer. This layer has high electrical resistance, especially under discontinuous current load, and acts as a resistor in series with the cathode. This is particularly undesirable for tubes used in computer applications, where they can stay without conducting current for extended periods of time.^[9]

Barium also sublimates from the heated cathode, and deposits on nearby structures. For electron tubes, where the grid is subjected to high temperatures and barium contamination would facilitate electron emission from the grid itself, higher proportion of calcium is added to the coating mix (up to 20% of calcium carbonate).^[9]

Boride cathodes[edit]

Lanthanum hexaboride (LaB₆) and cerium hexaboride (CeB₆) are used as the coating of some high-current cathodes. Hexaborides show low work function, around 2.5 eV. They are also resistant to poisoning. Cerium boride cathodes show lower evaporation rate at 1700 K than lanthanum boride, but it becomes equal at 1850 K and higher. Cerium boride cathodes have one and a half times the lifetime of lanthanum boride, due to its higher resistance to carbon contamination. Boride cathodes are about ten times as 'bright' as the tungsten ones and have 10-15 times longer lifetime. They are used e.g. in electron microscopes, microwave tubes, electron lithography, electron beam welding, X-Ray tubes, and free electron lasers. However these materials tend to be expensive.

Other hexaborides can be employed as well; examples are calcium hexaboride, strontium hexaboride, barium hexaboride, yttrium hexaboride, gadolinium hexaboride, samarium hexaboride, and thorium hexaboride.

Thoriated filaments[edit]

Slot Machine Cathode Poisoning Prevention Treatment

A common type of directly heated cathode, used in most high power transmitting tubes, is the thoriated tungsten filament, discovered in 1914 and made practical by Irving Langmuir in 1923.^[10] A small amount of thorium is added to the tungsten of the filament. The filament is heated white-hot, at about 2400 °C, and thorium atoms migrate to the surface of the filament and form the emissive layer. Heating the filament in a hydrocarbon atmosphere carburizes the surface and stabilizes the emissive layer. Thoriated filaments can have very long lifetimes and are resistant to the ion bombardment that occurs at high voltages, because fresh thorium continually diffuses to the surface, renewing the layer. They are used in nearly all high-power vacuum tubes for radio transmitters, and in some tubes for hi-fi amplifiers. Their lifetimes tend to be longer than those of oxide cathodes.^[11]

Thorium alternatives[edit]

Due to concerns about thorium radioactivity and toxicity, efforts have been made to find alternatives. One of them is zirconiated tungsten, where zirconium dioxide is used instead of thorium dioxide. Other replacement materials are lanthanum(III) oxide, yttrium(III) oxide, cerium(IV) oxide, and their mixtures.^[12]

Other materials[edit]

In addition to the listed oxides and borides, other materials can be used as well. Some examples are carbides and borides of transition metals, e.g. zirconium carbide, hafnium carbide, tantalum carbide, hafnium diboride, and their mixtures. Metals from groupsIIIB (scandium, yttrium, and some lanthanides, often gadolinium and samarium) and IVB (hafnium, zirconium, titanium) are usually chosen.^[12]

In addition to tungsten, other refractory metals and alloys can be used, e.g. tantalum, molybdenum and rhenium and their alloys.

A barrier layer of other material can be placed between the base metal and the emission layer, to inhibit chemical reaction between these. The material has to be resistant to high temperatures, have high melting point and very low vapor pressure, and be electrically conductive. Materials used can be e.g. tantalum diboride, titanium diboride, zirconium diboride, niobium diboride, tantalum carbide, zirconium carbide, tantalum nitride, and zirconium nitride.^[13]

Cathode heater[edit]

Slot Machine Cathode Poisoning Prevention Definition

A cathode heater is a heated wire filament used to heat the cathode in a vacuum tube or cathode ray tube. The cathode element has to achieve the required temperature in order for these tubes to function properly. This is why older electronics often need some time to 'warm up' after being powered on; this phenomenon can still be observed in the cathode ray tubes of some modern televisions and computer monitors. The cathode heats to a temperature that causes electrons to be 'boiled out' of its surface into the evacuated space in the tube, a process called thermionic emission. The temperature required for modern oxide-coated cathodes is around 800–1,000 °C (1,470–1,830 °F).

The cathode is usually in the form of a long narrow sheet metal cylinder at the center of the tube. The heater consists of a fine wire or ribbon, made of a high resistance metal alloy like nichrome, similar to the heating element in a toaster but finer. It runs through the center of the cathode, often being coiled on tiny insulating supports or bent into hairpin-like shapes to give enough surface area to produce the required heat. Typical heaters have a ceramic coating on the wire. When it's bent sharply at the ends of the cathode sleeve, the wire is exposed.The ends of the wire are electrically connected to two of the several pins protruding from the end of the tube. When current passes through the wire it becomes red hot, and the radiated heat strikes the inside surface of the cathode, heating it. The red or orange glow seen coming from operating vacuum tubes is produced by the heater.

There is not much room in the cathode, and the cathode is often built with the heater wire touching it. The inside of the cathode is insulated by a coating of alumina (aluminum oxide). This is not a very good insulator at high temperatures, therefore tubes have a rating for maximum voltage between cathode and heater, usually only 200 to 300 V.

Heaters require a low voltage, high current source of power. Miniature receiving tubes for line-operated equipment use on the order of 0.5 to 4 watts for heater power; high power tubes such as rectifiers or output tubes use on the order of 10 to 20 watts, and broadcast transmitter tubes might need a kilowatt or more to heat the cathode.^[14] The voltage required is usually 5 or 6 volts AC. This is supplied by a separate 'heater winding' on the device's power supply transformer that also supplies the higher voltages required by the tubes' plates and other electrodes. One approach used in transformerless line-operated radio and television receivers such as the All American Five is to connect all the tube heaters in series across the supply line. Since all the heaters are rated at the same current, they would share voltage according to their heater ratings.

Battery-operated radio sets used direct-current power for the heaters (commonly known as filaments), and tubes intended for battery sets were designed to use as little filament power as necessary, to economize on battery replacement. The final models of tube-equipped radio receivers were built with subminiature tubes using less than 50 mA for the heaters, but these types were developed at about the same time as transistors which replaced them.

Where leakage or stray fields from the heater circuit could potentially be coupled to the cathode, direct current is sometimes used for heater power. This eliminates a source of noise in sensitive audio or instrumentation circuits.

The majority of power required to operate low power tube equipment is consumed by the heaters. Transistors have no such power requirement, which is often a great advantage.

Failure modes[edit]

The emissive layers on coated cathodes degrade slowly with time, and much more quickly when the cathode is overloaded with too high current. The result is weakened emission and diminished power of the tubes, or in CRTs diminished brightness.

The activated electrodes can be destroyed by contact with oxygen or other chemicals (e.g. aluminium, or silicates), either present as residual gases, entering the tube via leaks, or released by outgassing or migration from the construction elements. This results in diminished emissivity. This process is known as cathode poisoning. High-reliability tubes had to be developed for the early Whirlwind computer, with filaments free of traces of silicon.

Slow degradation of the emissive layer and sudden burning and interruption of the filament are two main failure modes of vacuum tubes.

Transmitting tube hot cathode characteristics^[15][edit]

Material	Operating temperature	Emission efficacy	Specific emission
Tungsten	2500 K	5 mA/W	500 mA/cm2
Thoriated tungsten	2000 K	100 mA/W	5 A/cm2
Oxide coated	1000 K	500 mA/W	10 A/cm2
Barium aluminate	1300 K	400 mA/W	4 A/cm2

See also[edit]

References[edit]

1. ^ ^abcdefAvadhanulu, M.N.; P.G. Kshirsagar (1992). A Textbook Of Engineering Physics For B.E., B.Sc. S. Chand. pp. 345–348. ISBN978-8121908177.
2. ^ ^abFerris, Clifford 'Electron tube fundamentals' in Whitaker, Jerry C. (2013). The Electronics Handbook, 2nd Ed. CRC Press. pp. 354–356. ISBN978-1420036664.
3. ^Jones, Martin Hartley (1995). A Practical Introduction to Electronic Circuits. UK: Cambridge Univ. Press. p. 49. ISBN978-0521478793.
4. ^MA Electrode Requirements
5. ^'Archived copy'. Archived from the original on 2006-02-05. Retrieved 2006-02-14.CS1 maint: archived copy as title (link)
6. ^B. M. Weon; et al. (2003). 'Ba enhancement on the surface of oxide cathodes'. Journal of Vacuum Science and Technology B. 21 (5): 2184–2187. Bibcode:2003JVSTB..21.2184W. doi:10.1116/1.1612933.
7. ^B. M. Weon and J. H. Je (2005). 'Stretched exponential degradation of oxide cathodes'. Applied Surface Science. 251 (1–4): 59–63. Bibcode:2005ApSS..251...59W. doi:10.1016/j.apsusc.2005.03.164.
8. ^B. M. Weon; et al. (2005). 'Oxide cathodes for reliable electron sources'. Journal of Information Display. 6 (4): 35–39. doi:10.1080/15980316.2005.9651988.
9. ^ ^abElectron Tube Design, Radio Corporation of America, 1962
10. ^Turner page 7-37
11. ^'Archived copy'. Archived from the original on 2006-04-08. Retrieved 2006-02-14.CS1 maint: archived copy as title (link)
12. ^ ^abElectron emission materials and components: United States Patent 5911919
13. ^Thermionic cathode: United States Patent 4137476
14. ^Sōgo Okamura History of electron tubes, IOS Press, 1994 ISBN90-5199-145-2, pp. 106, 109, 120, 144, 174
15. ^L.W. Turner,(ed), Electronics Engineer's Reference Book, 4th ed. Newnes-Butterworth, London 1976 ISBN0408001682 pg. 7-36

External links[edit]

Slot Machine Cathode Poisoning Prevention Mechanism

• Lankshear, Peter (July 1996). 'Valve filament/heater voltages'(PDF). Electronics Australia. Retrieved 9 October 2017.