High reliability vacuum tube Manufacturer?  - Page 1
Forum section: electronics / projects

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 24, 2014, 01:52:17 pm
content: This might be somewhat of an exotic request but does anyone know of modern manufactures of medium power (~1Kw) vacuum tubes that can operate at HF radio frequencies and have a MIL-spec rating? I'm having sourcing issues with transistors that can handle the frequencies, power and radiation requirements of my environment so I thought I would look at the old school that I know can do this but I can't find a manufacturer.

author: richard.cs
author_rank: Super Contributor
timestamp: April 24, 2014, 02:47:37 pm
content: 1 kW is very much in the realm of solid state, usually multiple devices paralelled and the output of multiple such groups combined with transformers or similar. Search for "pallet amplifier", they're normally a few hundred Watts each and designed to be grouped together. There's not much use for valves in this application until you get over 10 kW although they are still made. You'll have to clarify what you mean by mil-spec though, certainly none exist that are specified to survive the mil-spec vibration tests.

author: retrolefty
author_rank: Super Contributor
timestamp: April 24, 2014, 04:45:12 pm
content: You might consider asking over at:http://forums.qrz.com/forumdisplay.php?89-Amateur-Radio-AmplifiersLots of ham still utilize high power vacuum tubes in their final amplifiers. Often heard that there are few companies actually building new vacuum tubes theses days, maybe just Russia and China of questionable quality, and only a few in the USA for special medical equipment at outrageous prices. There is a active market in NOS (new old stock) vacuum tubes because of the lack of new stock these days.

author: wraper
author_rank: Unknown
timestamp: April 24, 2014, 05:22:17 pm
content: Basically all you can get for a reasonable price is USSR NOS and made by Svetlana in Russia.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 24, 2014, 05:47:27 pm
content: go tohttp://eng.mil.ru/and email a request to exchange vacuum tubes for vodka. they will probobly ship you a MIG radar front end loaded with vacuum tubes for a few cases.Are vacuum tube NOS amplifiers cheaper then parallel solid state radio amplifiers?

author: dannyf
author_rank: Super Contributor
timestamp: April 24, 2014, 10:07:01 pm
content: QuoteProbably never will, just as you will not find a reputable manufacturer of Model T today.

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 24, 2014, 10:09:00 pm
content: CPII/Eimac?http://www.cpii.com/division.cfm/9

author: gregariz
author_rank: Frequent Contributor
timestamp: April 24, 2014, 10:40:49 pm
content: Quote from: qwaarjet on April 24, 2014, 01:52:17 pmhttp://www.communication-concepts.com/has kitted the some of the mfr reference designsotherwisehttp://www.rfparts.com/

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 24, 2014, 11:10:17 pm
content: Thanks for all the responses. I think I need to clarify a few things. I have already built a prototype high power amplifier using conventional power MOSFETs the issue is I need to move this design to a high radiation environment and conventional parts are not available that will Survive that. unfortunately conventional high-power RF amplifiers like traveling wave tubes or magnetrons are not available at the relatively low frequencies that I am using . That's why I started looking into old school vacuum tubes.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 24, 2014, 11:20:13 pm
content: I am so curious as to what you are building, it sounds like some crazy ass shit O0

author: dannyf
author_rank: Super Contributor
timestamp: April 24, 2014, 11:52:38 pm
content: QuoteI would suggest that you don't. Otherwise, men in black dresses may start show up at your doorsteps.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 24, 2014, 11:55:12 pm
content: Quote from: dannyf on April 24, 2014, 11:52:38 pm

author: Alphatronique
author_rank: Regular Contributor
timestamp: April 25, 2014, 12:23:16 am
content: HInot sure tube was good for hi-rad ,ionizing particle may make it arc or somewhere else on HV circuiteimac ans swetvania was normally good like 4CX1000 or 3-500Z or similar have lot aviable on marketlvdmos on shielded/leaded enclosure may look better solution and @50volt it may safer and not arcbut that look a strange/unsafe project , hope you not try to turn it into Krytron tube

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 25, 2014, 03:11:17 am
content: This is part of a R&D phase of plasma processing system that will ultimately be used in high earth orbit. I can't say what the exact details are but I'm currently trying to take are proof of concept system which used half a rack of equipment and fit it into a volume the size of a soda can. The current state of the art space parts don't operate at the powers and frequencies I want Im trying to get better educated on other options.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2014, 04:04:17 am
content: Hmm, interesting. Tubes have flown in space before (AFAIK, TWTs are still stock?), but they're hardly an attractive option for weight, or reliability (to a point). But if you're talking GHz, you'll probably have a hard time finding new technology with well understood failure modes (mature enough to consider launching).I can't imagine HF parts are hard to come by. BJTs and MOSFETs good for 100s of W and 10s to 100s of MHz have been available for nearly half a century. Maybe not the greatest efficiency, or the most handy packages (would be a pain to require liquid cooling, for instance), but I'd be surprised if nothing exists in the hi-rel sector.I'd make some comments regarding the matters of cost or availability, but... that's rather silly to point out when talking about spaceTim

author: zimzom
author_rank: Regular Contributor
timestamp: April 25, 2014, 04:26:47 am
content: How are the vacume tubes going to dissipate heat in low atmosphere environment effectively in your design? Odds are they are going to be high voltage so thats going to be a PITA.

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 25, 2014, 04:34:37 am
content: I spent considerable time looking for hirel transistors and what it breaks down to is a the parts that can handle the frequence are all low power <<100W and the parts that can handle the power don't work above ~1Mhz. So now I'm looking at having custom silicon made or finding a different technology like vacuum tubes or using a large number (and thus less reliable) of low power parts.The system also operates at very low duty cycles so thermal management is of much lower engineering priority than SWaP(Size Weight and Power) and reliability. Building the high voltage supply to drive a tube is also a process I am much more familiar with than the RF engineering.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2014, 04:35:16 am
content: Same way they do internally...radiationWith quite a bit of derating of course. Or better yet, liquid cooling.A 4CX250R will do a cool kilowatt under ideal conditions, of course you need to blow 250W worth of cooling gas over it. There was a similar part with a four-digit number, I don't remember what, that was entirely conduction cooled, which would be even better.Tim

author: calexanian
author_rank: Super Contributor
timestamp: April 25, 2014, 04:47:30 am
content: You have a few options. For high altitude testing you are going to have some problems. You need conduction cooling and long ionization arc paths. Some of this can be overcome by proper insulating methods. Depending on how much money you have, and this is all super high dollar stuff, you basically have 3L communications and CPI/Eimac. Raytheon, thales, burle, and a few other firms are still around as well. What altitude are we talking? Frequency? I need some more details before I can make any real suggestions. Also what kind of service? Tubes are inefficient. There are reasons they went away in flight systems in favor of low voltage radiation hardened BJT devices.

author: gregariz
author_rank: Frequent Contributor
timestamp: April 25, 2014, 04:55:24 am
content: Quote from: qwaarjet on April 24, 2014, 11:10:17 pmThere are high power switching mosfets available that are rad-hard (for switching supplies). These are not sold as RF transistors though.. but given your frequencies are low and you don't care about repeatability, I'd be inclined to see if I couldn't re-purpose some.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 25, 2014, 05:00:29 am
content: MIL spec?--Well,the Military use Solid State at power levels well above 1kW.Power capability?--I recently worked on Txs capable of 1.2kW continuously at 433MHz,in a SMI application.These used LDMOS devices which were packaged as two devices in each package.Each individual amplifier used one package,giving two amplifiers,which were paralleled to give 300watts.These were in turn paralleled to give 600watts,then paralleled again for 1200watts.Not much wrong with the concept,which is widely used,but we had a lot of strife with these units which were from the PRC.Eventually,they were retired,& we temporarily returned (against my advice) to tube technology.These latter units used new Eimac tubes,so they are still available.Since I retired,new Solid State units have been obtained from Tomco in South Australia.This company provides HF,VHF & UHF equipment to customers around the world,with a record of high reliability..I think you can probably shield a Solid State amplifier more cheaply than providing the complex coolingsystem needed for a tube in a restricted space aboard a spacecraft.

author: calexanian
author_rank: Super Contributor
timestamp: April 25, 2014, 05:06:53 am
content: I went back and re read your second post. For some reason my brain put high altitude in there. How high of an ionizing radiation exposure are we talking here? And at HF cant you have a nice amplifier safe out of the radiation and just run some coax?

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 05:21:24 am
content: this sounds like one of the coolest projects i read about on eevblog lolvacuum tubes in space O0

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 25, 2014, 05:45:48 am
content: Quote from: calexanian on April 25, 2014, 05:06:53 am~300kradshielding = weightsufficient shielding = lots of weightUnforchantly shieling is more than just a thin sheet of lead to block the radiation, it about mass it doesn't matter if you use a kg of lead or aluminium they block more or less the same. lead is nice because it low volume/ mass and is "cheap". In low earth orbit the magnetic field blocks most of the high energy electrons and you mostly deal with proton which are easily stopped with few mm of aluminum and consumer grade electronic can last many months to years without failing. However at high altitudes the electrons hit hard and generate xrays that damage system and require much more shieling. Cosmic rays will get you everywhere you are, they are less common than solar radiation but short of few hundred feet of rock there isn't much that you can do to shield them. a cosmic ray strike is the atomic equivalent of a playing billiards with a rifle, with the impact casing a spray of high energy particles and gamma rays striking more atoms in your satellite wreaking all sorts of chaos .

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 25, 2014, 05:55:31 am
content: Quote from: calexanian on April 25, 2014, 04:47:30 am14Mhz 1000W ~1 second pulse ~every few hundred minutes

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 25, 2014, 06:38:45 am
content: It's a tough project but I think do-able.I would seriously look at a water cooled tube or a tube that can be adapted to liquid cooling. I'm not sure what liquid will remain liquid at very low temperatures though.You would also need to derate it considerable for reliability. Maybe even two amplifiers for redundancy, coupled together with a Wilkinson combiner.Your can then concentrate your effort on the HV SMPS for the anode and filiment voltages. Also seriously derated and liquid cooled.I think the thermal aspect of the project would be the major hurdle.Dick

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 06:52:40 am
content: out of curiosity what is the standby wattage of vacuum tube? If you transmit 1000W in bursts how many watts will still need to be dissipated by just keeping the filaments good to go?Can a vacuum tube be powered down completely then powered up shortly prior to transmission and then turned off? or will this reduce the life considerably? Maybe putting three uncooled tubes in for "planned obsolescence" is a better solution if the project only has a limited life span. Much simpler too.that duty cycle is extreeeeeemly low. Will it really get that hot transmitting for 1 second? Can a liquid really help if its just 1 second of heat....I always imagined water cooling useful in situations where there is continuous heat production, so the water could be circulated. Wouldn't a normal heat sink be better for this application? I mean copper/aluminum should technically absorb more heat then the water, right?Can a significant amount of heat even pass through the glass casing of the tube in 1 second of transmission?

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 25, 2014, 07:05:30 am
content: 14Mhz 1000W ~1 second pulse ~every few hundred minutes.I missed this post.This changes everything. The average dissipation is tiny so forget water cooling.In fact I wouldn't even go with a tube if at all possible due to the filament having to be continuously powered.Maybe bipolar transistors are more radiation tolerant than MOSFET's and should be considered. Their power output also droops less than MOSFET's in pulse applications.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 07:07:43 am
content: Quote from: Richard Head on April 25, 2014, 07:05:30 amwhy must the filament be continuously powered?I read that low earth orbit satellites have a average life time of 5 years, if this makes a difference at all. I just hope people don't forget this fact proposing solutions that are meant to last 30 years (i have no idea about the life expectancy of tube stuff though)I calculated that at 1 pulse every 200 minutes the tube over 5 years will transmit 13140 times. So it only needs to survive 13000 power up cycles.*inrush current limiting on the filaments should be strongly considered if its being cycled on and off.http://www.ok1rr.com/tubes/burle/Techniques-to-Extend-the-Service-Life-of-High-Power-Vacuum-Tubes.pdfpage 2 has information on what happens, but it seems to focus on inrush current damage which seems easy enough to avoid... I actually can't believe that inrush currnet protection is not built into those vacuum tubes.. I mean come on they are spending 400,000$ a year on them according to the article! crazy! I wonder how much the life could be improved through gentle heating...maybe you could make it work with a few tubes that switch in.Discussions with tube designers havesuggested that the “Black Heat” or standby filamentvoltage should be between 25 and 40 percent of therated filament voltage. This range will produce atemperature high enough to keep the filament above600 degrees centigrade area where the Miller-LarsonEffect occurs and sometimes low enough so thatforced cooling is not required during stand-by.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 25, 2014, 07:09:00 am
content: Quote from: qwaarjet on April 25, 2014, 05:45:48 amIf you are worried about naturally occurring radiation-------all the work has been done,there are lots of satellites up there!Crud from your plasma,is another question altogether!If that is what concerns you,& you are sharing a "bird" how do the other people feel about possible unforseen problems?

author: vk6zgo
author_rank: Super Contributor
timestamp: April 25, 2014, 07:17:53 am
content: Quote from: SArepairman on April 25, 2014, 07:07:43 amCan't see any reason---the filaments could be gracefully brought up about a minute beforehand- do the pulse,allow another minute to cool down,then turn them off.That should be plenty of time--the 13kW NECs at TVW7 were up & running from cold in around 19 seconds,from memory.Admittedly,there is a lot of difference between room temp & space!

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 25, 2014, 09:05:34 am
content: Yes, I think powering them up a minute or two beforehand is ok actually but I reckon a semiconductor solution should be sought if at all possible.If semiconductors can be used I would opt for a class E amplifier if possible due to their high efficiency. That means MOSFET's though which are probably a problem due to the radiation problem.

author: jpb
author_rank: Super Contributor
timestamp: April 25, 2014, 11:57:51 am
content: What about SiC Mosfets?Here is an (old) paper from Cree on using them at VHF:http://www.cree.com/sitecore%20modules/web/~/media/Files/Cree/RF/Papers%20and%20Articles/ClassE%20Silicon%20Carbide%20VHF%20Power%20Amplifier.pdf#search=%22VHF%22I think SiC is potentially radiation hard as it is wide band gap (about 3V)

author: richard.cs
author_rank: Super Contributor
timestamp: April 25, 2014, 11:59:19 am
content: I would still think a solid state solution is possible here, but if it's going into space then you have budget for custom valves if you want them :-)Some points to consider:As has been mentioned not all valves are good in high radiation environmentsYou'll need to discuss launch vibration with the manufacturers, but don't expect them to know the answers. Most of the designers are long since retired and they keep just churning out old designs.You should expect to have to supply 50-100W of heater power, for at least a few seconds before transmit and maybe up to 30 seconds depending of cathode design (don't just assume directly-heated cathodes are quick to warm up).Linked to the above two points, remember that a normal transmitter valve is designed to operate bolted to the floor in a temperature controlled room, powered up continuously until the day it fails. A maximum of one power cycle per day for 10 year valve life is a typical specification.Valves have been flown without envelopes before now. The whole assembly is built in a clean room but not evactuated, even in low earth orbit the air pressure is lower than in the best valves so it'll work once it gets into space but weighs a lot less. Pre-flight testing is left as an excersise to the reader

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 25, 2014, 12:23:57 pm
content: There were special transmitting valves made for mobile radio service that were designed to have the filament cycled with each transmission. They came up to temperature in <1 second. A typical example is the YL1030:http://www.r-type.org/exhib/aad0308.htmThere were a whole series of these valves, but I don't think any got up into the 1 kW range.

author: calexanian
author_rank: Super Contributor
timestamp: April 25, 2014, 02:23:08 pm
content: Ok, now we are getting somewhere. For high ionization conditions "Most" oxide cathodes are out. What plate voltage are you invisioning? Also they do not like thermal cycling. Thoriated tungsten or thoria bonded are the way to go. Thoria bonded is really the best over all.

author: Alphatronique
author_rank: Regular Contributor
timestamp: April 25, 2014, 02:30:41 pm
content: Hithat reading may help you a bit ..http://www.advantechwireless.com/wp-content/uploads/WP-A-new-generation-of-Gallium-Nitride.pdfseem that new telecom sat turn to solid-state to

author: woodchips
author_rank: Frequent Contributor
timestamp: April 25, 2014, 02:59:24 pm
content: What about e2v, who used to be known as English Electric Valve Co?

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 05:44:59 pm
content: http://www.ok1rr.com/tubes/burle/Techniques-to-Extend-the-Service-Life-of-High-Power-Vacuum-Tubes.pdfI edited my post right before richard head responded, I figured it might have been over looked.I also made some sample calculations that this device, over the course of a typical 5 year LEO satellite life would be powered up 13000 times if it was transmitting every 200 minutes. I made the suggestion to use parallel vacuum tubes.richard CS wrote:. A maximum of one power cycle per day for 10 year valve life is a typical specification.so, that is, 365*10= 3650 times. So he would need 3-4 tubes, assuming this is accurate and that life cannot be extended by gradual heating.*in exchange for the help in this thread you should get EEVBLOG written on the side of your satellite lol and a picture of dave jones so aliens can abduct him

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 25, 2014, 05:59:11 pm
content: Quote from: SArepairman on April 25, 2014, 05:44:59 pmWell I don't think I can do that for this mission but I do have another satellite going up on falcon heavy in 2016 that I probably could sneak a message into.

author: richard.cs
author_rank: Super Contributor
timestamp: April 25, 2014, 06:04:18 pm
content: Quote from: woodchips on April 25, 2014, 02:59:24 pmThey still exist, I've used them for work before and they'll also design the rest of the RF stuff for a price. I have no idea if they make anything that small.Quote from: SArepairman on April 25, 2014, 05:44:59 pmThis is normal for larger transmitting valves, but may only mean that's all the manufacturer has tested (because even that is a lot of cycles in their normal application) rather than that they fail at 4000 cycles.One further point to consider, if you're taking a water-cooled valve and cooling it with another fluid (lower specific heat capacity) and/or cannot maintain the coolant inlet temperature and flow rate then you may have to de-rate it and therefore use a larger valve than you expect. On the other hand the low duty cycle works in your favour, there's a lot of metal in the anode so the thermal time constant is pretty long. Finally, don't forget that the cathode heat has to go somewhere too, and if you end up with a 10 second warmup time than it's a comparable amount of energy to your anode dissipation.

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2014, 07:06:01 pm
content: If the duty cycle is that low just use a semiconductor amplifier and cut the heatsink size down, and use copper plate instead of aluminium to both increase thermal capacity and reduce thermal resistance. Use ceramic insulating washers to withstand the voltage and use a thermal epoxy to bond to the heatsink and the device, not a paste. That way you will have enough mass to handle the short pulse of heat and integrate it to dissipate during the longer off time. Preferably silver plate the milled heat spreader to protect it from corrosion during assembly and test, and give a cover coat of hard gold flash over the silver. Then you both have a compact system and a lighter one, and the copper plate can easily be integrated into a card to allow you to use the spacecraft frame as a heat dissipation device during the off times.A 1 second pulse will barely get the device heat spreaders to start heating up, and the mass of copper on them will give plenty of time to cool the die.You will need to look at cycle life for the devices, but as you probably will only need 20000 cycles of operation ( probably you will use around half in testing) overall most TO3 packages will survive this easily. TO220 might have issues, but that is easy to solve by having a lot of smaller amplifiers combined into the one pulse, and a simple monitoring set to enable faulty units to be switched out if they fail, and simply have a few extra stages to give a hot reserve.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 07:35:05 pm
content: Quote from: SeanB on April 25, 2014, 07:06:01 pmbut what about the radiation?

author: calexanian
author_rank: Super Contributor
timestamp: April 25, 2014, 08:58:31 pm
content: Contact Microsemi. they had Rad-Hard parts that can be used down at HF. Solid state really is the way to go here. How are you going to generate the high voltage for the power tubes? Mechanical vibrator? Synchro motor? Rad-Hard switching power supply would be harder to build than the RF amp!

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 25, 2014, 11:27:09 pm
content: how about a HV transformer?

author: calexanian
author_rank: Super Contributor
timestamp: April 26, 2014, 12:36:01 am
content: Quote from: SArepairman on April 25, 2014, 11:27:09 pmWeight.. And bulk. most flight systems are 26 or 48 volts if I recall.. RF transistors are made to be in that voltage and power output range.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2014, 01:57:54 am
content: In one of his earlier posts,the OP says"I'm currently trying to take are proof of concept system which used half a rack of equipment and fit it into a volume the size of a soda can"What is he referring to here?If he thinks he is going to shrink a 1kW HF RF amplifier,complete wih power supply & cooling,down to much less than about 2 rack units,he is overly ambitious.What is achievable at UHF rapidly becomes much less so as the frequency is reduced.Even broadband HF Amplifiers require LC networks,which at around 14Mhz,& at the required power levels,will not be small.The most efficient circuitry would use narrow band resonant LC circuits,which again would not be small.Harmonics of 14MHz need to be reduced to a low level if you are sharing the spacecraft with other systems,probably entailing additional LP networks,at least in the broadband case.I don't know a lot about plasma,but from what I've read,it produces wideband RF noise.Again,sharing a spacecraft??

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 26, 2014, 03:01:12 am
content: Laboratory studies have already been conducted using commercial RF supplies with the addition of custom matching networks for the plasma processing system. The stage I'm at now is miniaturizing , the laboratory equipment is general purposes and thus contain functionality that I don't need for the final product, the device I'm building is purpose built to make a lot of RF power for a few hundred ms. Since the system operates for a very short time and has long interval between uses thermal management is not a major issue, even at 50% efficiency the system isn't on long enough heat the parts much more than 50C or so with no cooling on them at all.This system will be tested and characterized with other satellite sub-system over the course of thousands of hours in environmental chambers; If there are noise issue they will be discovered long before we go into space. Current results indicate that there will be little interference.My review of current rad hard /hirel manufactures has not found parts that can operate at the power AND frequency I need. There are plenty of hirel silicon parts that can operate at 14Mhz but there max power is very low, so a unworkably large number of component would be needed. Power mosfets are available at the power I need but as of yet I have not been able to drive them at the frequencies I need.The idea of using vacuum tubes was they are inherently rad hard (no crystal lattice to destroy) and I would only have to built a few thousand volt power supply with available power mosfets. A task that I am fairly comfortable with. The tubes would not be on long enough to require active cooling (worst case use thermal management wax). However prior to this discussion I had no idea where to start looking for reliable source of tubes with properties I needed.The most likely path forward will be using a RF MOSFET and having it re-engineered for space at the fab this look into vacuum tubes was me hedging my bets if it turned out to not be possible do to some limitation in fab.Again thanks for all the helpful comments.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 26, 2014, 03:17:45 am
content: Something to keep in mind, if interference isn't a problem then there's probably no point in staying in the ISM band, at least exactly. That is a huge drawback to terrestrial supplies, which must operate fixed frequency, tolerate extreme SWR and have expensive, bulky adjustable (often adaptive, servo driven) tuning networks to couple and ignite the plasma. Something much more akin to a CCFL lamp driver or induction heater may be easier to work with.Tim

author: calexanian
author_rank: Super Contributor
timestamp: April 26, 2014, 03:28:43 am
content: I am afraid without knowing all of the design goal limitations and parameters I is going to be very difficult to help you.. I am sure there is a solution, however it will most likely be extremely niche.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2014, 03:44:15 am
content: Quote from: T3sl4co1l on April 26, 2014, 03:17:45 amAnother point is that 14MHz is not an ISM frequency---it is the beginning of the Amateur Radio 20m Band,which extends to 14.35MHz.Maybe he is really using 13.65MHz,which is an ISM frequency.

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 29, 2014, 06:49:27 am
content: A plasma is not always a serious noise generator.I worked on a military project some years ago where we used a xenon lamp. The lamp was an arc type that ionised the xenon and a constant current was forced through the arc. Everyone was concerned about the noise from the arc as the product had to comply with MIL STD 461C. As it turned out the arc generated no appreciable noise compared to the switchmode power supplies. We didn't even have to shield the lamp. Maybe I was just lucky!Dick

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 29, 2014, 07:39:40 am
content: Hmm, good to know I guess. I'm sure it depends on the magnitude... a hot, high pressure arc having a low impedance, while a glow discharge has a higher impedance = more opportunity for voltage noise.Fluorescent lights are notoriously noisy, but that's almost always a direct result of shitty ballasts... I don't know if anyone's complained of actually identifiable discharge noise. Or neon lights, also a glow discharge. Instability and parasitic resonance is the big deal, which should be minimal in a clean design.Tim

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 29, 2014, 10:27:55 am
content: In my case the arc current was accurately controlled by a control loop so current fluctuations were minimal.

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 30, 2014, 04:28:02 am
content: The plasma generated by the system is mostly well contained in side of a test vessel so radiated noise should be minimal. Noise in our system is mostly caused by ground loops so can be controlled with proper cabling.

author: David Hess
author_rank: Super Contributor
timestamp: May 02, 2014, 01:09:19 am
content: I recommend reading "Getting the Most Out of Vacuum Tubes" by Robert B. Tomer:http://www.nutshellhifi.com/library/MostVacuumTubes.pdfLow operating temperature is important for high reliability so derating will be important. Lowering the heater voltage may be acceptable to increase life (maybe qualify the tube to determine this?) but I would also be careful about cathode stripping by operating the tube before the cathode has reached operating temperature.