Degassing Your Eimac 3-500Z and 4-400A Tubes
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- Опубліковано 19 кві 2020
- I am trying all the suggestions with no success so far. I am pretty close to giving up completely on this very nice looking Eimac 4-400A but I have one more thing I have to do before completely giving up.
Further reading from Eimac Application Bulletin #18 www.cpii.com/docs/related/22/...
"The key to extending the life of a thoriated tungsten filament
emitter is to control operating temperature. Emitter temperature is a function of the total RMS power applied to the filament. Thus, filament voltage control is temperature control,
because temperature varies directly with voltage. Figure 8
shows that useful tube life can vary significantly with only a 5%
change in filament voltage.
NOTE: If the filament voltage cannot be regulated to within
± 3%, the filament should always be operated at the rated
nominal voltage specified on the data sheet.
It should be noted that there is a danger to operating the emitter too much on the “cold” temperature side. It may become
“poisoned.” A cold filament acts as a getter; that is, it attracts
contaminants. When a contaminant becomes attached to the
surface of the emitter, the affected area of the emitter is rendered inactive, causing loss of emission. Should this happen,
recovery is possible by operating the filament at full voltage
for a period of time. Closely monitored operation of the filament at slightly below the rated nominal voltage, however,
can extend tube life, if done properly.
Note that these filament management techniques should not be
applied to oxide cathode tubes, such as the 3CX1500A7/8877.
Running oxide cathodes too cold will result in internal arcs; and
once that happens, an oxide cathode tube is not recoverable."
From Application Bulletin # 21
www.cpii.com/docs/related/22/...
"Large power tubes are subjected to very rigorous processing
during exhaust pumping at the time of manufacture. Active
elements are processed at temperatures several hundred degrees Celsius higher than that to be expected in actual use.
This is done to drive off surface and subsurface gas from the
metals to minimize the possibility of these being released during service life of the tube." - Розваги
Old Thread/New Comment: W1ZY
What you are doing in the video is what is done to "rejuvenate" the cathode to "restore" a "soft" tube. Make sure you are blowing air over the pins of 3-500 family of tubes.
_To deGass a 3-500Z_ , you must use a _different technique_ . A _different setup_ , if you are still interested in experimenting with this.
Here's what you need:
1. 0 - 40 VDC variable supply (to adjust + grid bias)
2. HV Plate Supply on Variac (0 - 3,300 VDC)
3. Various VOMs for grid current, plate current & plate voltage.
In the set up in your video, you make the following changes:
- detatch the grid from the plate and connect it to the + of the 0 - 40 VDC variable supply.
- attach the plate to the + of the HV supply on a Variac.
- attach the cathode (filament) to the - of the HV supply
With a 3-500Z tube flashing over like the 4-400A popping fuses in your amp, you are going to try to heat up the plate by raising the HV voltage and adjust the grid bias without causing the gas to glow inside the tube. You adjust these voltages to get about 300 to 400 mA of plate current and no more than 125 mA on the grid. In the beginning you want to do with minimum plate voltage (about 1200 VDC) to avoid like the plague any flashover. When the plate glows red with dissipation, let it cook for an hour.
Then readjust the two voltages to get the 300 to 400 mA of plate current at a slightly higher plate HV, _but not so much as to flashover the gassy tube_ like the 4-400A did in your amp.
Let the tube cook for a while, making certain that lots of air blows, especially on the pins.
Then increase the HV and readjust the grid bias to for 300 to 400 mA of plate current without causing the tube to flashover. Cook.
The point is to inch the B+ until you are at 3,300 VDC (or so) without flashing over the tube. If the tube is dead, you aint gonna get to the original specified B+.
Some old timers can do this by pushing up the HV to the point where flashover is just about to occur, and then back down the HV 250 VDC, readjust grid bias for 300 to 400 mA Ip, and then cook the sumbitch for a few hours. Then they inch the HV up a little more, right before flashover, adjust grid bias, etc. and cook some more.
This may or may not activate the "getter" to get the tube to operate at its specified anode voltage.
There is a good discussion of this here:
lists.contesting.com/_amps/2011-11/msg00011.html
I enjoy your channel.
PS
Regarding the Eimac stuff you quoted about tubes with external anodes, like 8877s, the "getter" is on the cathode, rather than the plate. So to degass, just run the filaments at the specified voltage without any anode voltage-none needed. This activates the "getter" on the cathode. Make sure a blower moves lots of air over the pins and up through the fins.
73s,
BILL W1ZY
Thanks Bill,
You have provided a very nice detailed explanation and link to possibly save a rare 3-500Z. I know everyone appreciates that.
I think what I may be missing all these years, is I never use 3-500Z's. I had a couple of Chinese made 3-500Z tubes a few years back and even made a video using them but got more output from 40+ year old Eimac 3-400Z's in my homebrew amp. I sold the 3-500Z's.
With that said, it seems the real-world life with the 3-500Z is somewhat unique and cannot be directly compared to the 4-400A which I have used most in my builds. There seems to be issues with possible seal leakage around base pins and plate seal and maybe that along with other issues the mighty 3-500Z tends to have, is something that I am just not familiar with.
I don't want to discourage anyone form trying to de-gas or rejuvenate an old tube but the ones I have tried, just hasn't worked out for me.
There is information all over the Internet that if a power tube has not been used for a year or two or three, it is necessary to let the filaments run a some unspecified lengthy time before applying high voltage. With that in mind, I can say for sure, that I just plug my inventory of tubes in, let the filament warm up for maybe a minute and apply 4KV and nothing ever goes wrong. Am I just lucky? Maybe that is where my experience "bias" comes in about the rejuvenating and degassing processes.
However... if I ever do get a nice single or set of Eimac 3-500Z tubes, you can bet I will follow the wisdom of the past and treat them with the utmost care before throwing HV on them. I certainly would feel a fool if I put a pair in one of my amps and destroyed them right out of the box and wondered the rest of my life if I had "cooked" them just a little, they might work perfectly. 🙂
Thanks again for your time and comments. 73 WA4QGA
I've worked with high vacuum and ultra high vacuum systems since 1979 for high energy ion accelerators, electron microscopes and x-ray microscopes. These are all systems that involve the usage of vacuum chanbers containing electrodes, filaments and certain materials used for physical or chemical processes.
As others have said, the only way to remove gas from a vacuum chamber is to pump it out. It's important to note that there are vacuum pumps that are capture pumps. They either use cryogenic temperatures to capture the gas inside a porous desecant such as active charcoal or by a chemical reaction as does the titanium metal with its' high affinity to react with oxygen or halogen gases and this is in fact the metal used in the "getter" flash inside electron tubes. Gases cas be adsorbed or desorbed into or out of surfaces inside a vacuum chamber however, heating any surface will cause gases to leave it rather than become absorbed into it.
There is one other method to reduce the pressure inside a sealed chamber. You can deposit metal onto it while it's absorbed into a surface, trapping it underneath the fresh coating. It's very remotely possible to overheat only the filament to cause it to partially evaporate tungsten metal that can then be attracted to any cold surfaces nearby. If you could do that inside the tube's plate it might work but simply using the tube again would heat the plate and cause it to desorb the gas again. You're simply going to have to vent the chamber and connect it to a turbomoleculat pump then reseal it. Clearly it's cheaper to buy a new tube.
By the way, rather than using a piece of equipment to test a tube for gassyness, try connecting it to a Megger. That's a high voltage ohmmeter that contains a small high voltage power supply to get readings. There's no need to heat the filament. Just connect one lead of the Megger to the anode and the other to the cathode. If the tube contains a good high vacuum it'll indicate many Giga ohms. A gassy tube will breakdown at 1000V to 2500V indicating a HV short. Save money and time and get rid of gassy tubes. They're never going to work ever again no matter what anyone says or does, unless they open it and repump it.
The megger is a grand idea. I have one that goes to 5KV. I think I have saved some gassy tubes - I save bad tubes in a special box, labeled to throw them away at my passing so they don't end up on Ebay as NOS... 🙂 I keep them to "model" my amplifier builds so I don't have to risk my good tubes in testing layouts. I will see what I can find and try the megger and may make a video of it. I have never bought into the idea of heating up tubes after they have been in storage - except Hg rectifiers, of course. I just plug them in, give them the courtesy of having the filament on for 30 seconds, while I prepare to run in case of HV arcing, and pour the HV to them. Thanks for the information...
@@ElPasoTubeAmps A Megger is fast and simple for a quick test for tube gassiness. You don't even need to use HV DC. AC is fine and if you have only DC it doesn't make any difference what polarity you apply the voltage. You're looking to ionize gas molecules that don't belong inside the tube. The HV you apply will spray free electrons at the gas, knocking off valance electrons in the atoms of gas, thereby charging them into positive ions . The ions will be attracted to the negative electrode while the stripped-off electrons are attracted to the positive electrode. The anode in this case can be the tube's filament or, even the grid and it can be done at room temperature because the test uses Field Emission rather than Thermionic Emission. If you measure any current at all, that means the vacuum has been breached by an air leak and nothing, short of re-pumping the tube is going to ever fix it. You can alternately use a Hi-Pot which is basically an AC, High Voltage ohmmeter that reads out in current to test for HV Leakage current. I've got many decades of experience working with High Vacuum and HV systems and apparatus up to 250KV DC and industrial Tube / solid state RF Amps up to 8KW. I repair those and work with specialty X-ray systems. I'm not just taking guesses here. I know what I'm talking about. Try your Megger and see how fast and easy this test is. No other tool is required.
Right on man I want to learn more about tubes and that particular type of technology very fascinating. My dad was a tube fanatic.
Thou art surely brave and courageous, David :-) I know that feeling of turning up the voltage and just hoping you connected everything correctly and that you can get to the "off" switch, if need be, before the whole enchilada becomes a four-alarm fire.
When things start going to hell, I can never get to the off switch soon enough. I am like a cat in front of a rattlesnake.
I am starting to ask this question to individuals as I know you are one of the ones that will tell me the truth. Have you ever, personally owned, or personally witnessed, a tube failing and ionizing like the one in my video that has been made to work after the degassing procedure? There is, in my opinion, confirmation bias that is promoted thru ham radio folk-lore and amplified by the Internet about this procedure. I do not believe it will work until someone can tell me that they have experienced it personally, in real-time, a failing tube fixed by this degassing procedure.
@@ElPasoTubeAmps Good morning, David. First of all, your knowledge of electronics and 'all things tube' is built, not just from "book-learning", but from your years of real-world applications, experiments and failures, as well. If I were you, I would trust my observations and the conclusions i reach after such countless attempts. I have seen plenty of ionization. It's rather beautiful to look at - laugh - except when you realize your valuable tube is self-destructing! I see no way to recondition any tube after the vacuum has been breached. It's much like "reforming" old electrolytics. Although, you may get a cap that functions, it never functions as well as when it was fresh. I never use electrolytics - I use Solen metallized polypropylene caps for all my filtering. Expensive and large but worth every penny. The graphite-plate KT88s produced by Northern Electric out of Canada (around $200 each), for example, are made to run with glowing red plates, that's how they are designed. They look like they are ready to run away and they glow like a campfire but sound unbelievable, from all reports. Those are some of the only tubes I have seen that are to be operated as if they are ready to melt-down. How is it possible to remove gas from a breached tube? It cannot be done with conventional audio power tubes so how is it possible with large transmitting tubes? If the getters can't remove the contaminates, the tube is toast. I believe the EIMAC beauties suffer from the same affliction. If the zirconium-coated plate (I believe I have that right) cannot remove any gas from the tube, it probably will never be removed and you might as well use it as a night-light. So, in my experience, a dead tube is a dead tube is a dead tube. Let us know if some miracle happens on your work-bench :-) BTW, as per my suggestion of using TV damper diodes (6AU4, for example) as rectifiers, although the filaments are designed to operate, indirectly heated, at 6.3 volts, the dirty little secret is that they work with a 5 volt filament supply with virtually no degradation of performance. They hold a rock-steady voltage and pass plenty of current even when operated from a 5 volt supply - very cool, indeed! Thanks for your generous replies and dedication to the craft.
When I have used this technique in the past, I filtered the DC using a 200uF/200V electrolytic 'liberated' from a switching power supply. Smoother DC makes it possible to draw more plate current at an even lower voltage. I'm in the middle of a big car repair, but when I'm done with that, I'll take a short video of this done to a pair of 833s, destined to serve in a low-band amp build.
I love 833A's and look forward to your video. I have two soft one and an amplifier that uses one. Maybe I should try it also.
I enjoy your videos, I noticed your test leads. I’ve had consistency problems with the multipack test leads and build my own.
dang you know i was wondering about those , tks for a tip, i will built some too
At this point, it seems that the tube is now only good for a night light :) at least it won't go to waste .) I've actually done that with a defective 4-400A I have it around somewhere. I mounted the socket on a metal base, and connected the filament leads to an external transformer. It was on my night stand for years :)
Are those 872's? It has been a while since I have seen some. 73, Jim
Ballast the anode with a suitably sized choke or light bulb so you can run it at 1-2A continously. The reason it's running away is because the gas is ionising and lowering the impedance like a thyratron. That shouldn't be a problem as long as you can keep the current from going too high. If you can keep it cooking at a few amps for an extended period it might just getter away the gas.
I remember reading in an old tube manual (a 1940s college lab textbook), that 'flashing' the cathode like you did for the soft tube, and is also done at the factory, brings a new layer of thoria to the surface of the carburized cathode. While not a fix for every problem, if emission is low, it can be a band-aid fix. It also said most directly-heated cathodes have much more than enough thoria, and also an emission capacity that far exceeds the tube's needs.
I understand what you are saying. Some time back I measured a high-end 12AU7 family of tubes and then accidentally dropped it. I figured that was the end of it... so I tested it immediately and it was considerably stronger than before I dropped it. Naturally, I was surprised. Sometime later I decided to do the same thing on a "controlled basis" and I found nothing different before and after the drop. Hmmmmm... During the measurement of these transmitting tubes, I was experimenting with different tubes and found that the bad tube would "run away" in current and ionize and blow the fuse whereas the good tubes would not. A nonchalant measurement before and after heating the cathodes to currents 3X their normal operating parameter seemed, at least in one tube, to improve it. Sometimes a moment is hard to duplicate but it still might be true. Old black and white TV CRTs would get weak and the fix for them was to heat the filament extra hot as you mentioned and help clean off the cathode as they are thorium tungsten filaments. Another method for the TV CRTs was to simply add in a filament transformer that was above the 6 volts that the filament was rated at, i.e. run it at maybe 7 or 8 volts to really heat it up. It worked... Raising the filament voltage works on regular vacuum tubes also not just the thorium-tungsten type.
@@ElPasoTubeAmps Doesn't grid ground and biasing voltage dictate whether or not a tube will "Run away"!
@@ericdee6802 Grounded grid amplifiers are made with tubes that have a lot of gain, like an 811A which has a gain (also known as mu) of 160. The Eimac 3-400Z, 3-500Z, 3-1000Z and the 4-400A family of tetrode tubes strapped as triodes, have a gain of 200. They make great GG amplifiers and require no bias - thus called zero bias triodes. Low gain tubes, for example, a 833A is a medium gain tube and does require a negative bias of about -90 volts for a plate voltage of 4000 to keep the plate current under control. The low gain tubes need to be grid driven instead of cathode driven and they have to be neutralized as they are run as tuned-grid-tuned-plate (TGTP). It is all about the grid structure inside the tube. Hi gain tubes have a very fine closely wound grid structure. More spacing in the grid structure lowers the gain but increases the linearity. Can't have everything... Low gain tubes like the 300B are very linear and make good audio amplifiers. Low gain high-power tubes, again like the 833A, make great class-C plate modulated amplifiers for small AM radio stations that used to be everywhere in the USA. The Gates amplifiers/transmitters used to run two 833A in the final and plate modulate them with another pair of 833A for four beautiful tubes in the transmitter.
Shame it's dead but I always think they make nice ornaments to put on your mantle piece, had some 4-250 that were bad but they looked nice with the heaters running
The only thing I can think of next for you to try is to use the current to heat the cathode and use a induction heater around the tube to heat the plate to red hot to get the getter material activated. That is generally what they do at the factory 8s some placess
I did heat the plate up to red and dissipating up to 500 watts. I could increase the current to 5 to 7 amps at 100 volts but it became critical I kept my hand on the Variac as it could run away and ionize. Good tubes never did run-away. This tube was beyond help and I sent it back and the good gentleman gave me my money back.
Rebuild your transmitting tubes. A company in Florida will put new components inside the glass envelop for a fee of 1/2 the cost of a N.O.S. tube. I used them 20 years ago on a pair of 4-400z tubes for my Swan amplifier and my Heath 3-500z' s for the 220. After all these years of operating, the tubes are still strong, even on 10M. I hope they still exist as I have a number of 572B tubes that need their expertise. I have a two tube 6M amp homebrew from an old 73 mag I built myself, the 811A' s are still cheap enough to not bother rebuilding - yet. If you can get a bunch of N.O.S. 811A tubes and match them up with a transconductance tube tester within 10% of each other, the neutralizer in the amp can make up the difference. I have an amp that uses 6 TV sweep tubes in parallel (6KD6) that I will put on the air someday on 6M. Tube amps can take much more mismatch abuse than semiconductor amps, sometimes the antenna waving its elements too much in a strong wind can ruin the components. Tube amps are a much better choice.
what company in Florida?
Just wondering could you put the tube in a vacuum chamber to get the gas out it would probably be a very slow process if the vacuum chamber is very close to the size of the tube and has a perfect seal with a micron gauge if the gauge reads higher its sucking gas from the tube idk might be worth a shot on rare or expensive tubes
If the tube took 60 years to "go to air" then it'll take another 60 years in a vacuum chamber to get back to vacuum. In this case he should ballast the anode so he can get the anode sufficiently hot without the setup running away. If that doesn't getter the oxygen out it's a paperweight.
This idea of defassing tubes reminds me of the reforming caps stuff. If air gets into the tube no matter what you do, the air won't get out. One of the most difficult parts of the tube to build are the seals between glass and the electrodes. Generally if the tube is used periodically it tends to be less suceptible to fail than tubes that are NOS. Maybe it is because of the heat tempering the glass at the seals, I don't know. About reforming caps, yes, a bunch of people will fall over me, but, when chemestry and materials become bad, they are bad. The only exception in reforming caps would be "forming" electrolitic caps, when they are new. But trying to revive a 60 year old crappy capacitor won't happen.
There's a difference between a tube going to air and a tube being gassy. If it's gone to air, it's dead, no question (and some eimacs are known to have issues with pin-to-glass seals). If it's gassy, it just means the vacuum is contaminated with products of off-gassing from the various elements in the tube. Don't think this is such an issue in smaller tubes, but the anode in large tubes like these acts as a getter to absorb those impurities. If a tube has sat on the shelf for too long without being heated enough to "getter" it, it can be "gassy". The fact the filament in this tube didn't go up in smoke, and the fact he was able to get anode voltage above 1000v without drama means it likely still has vacuum. The arcing indicates gassing contamination and it may be too far gone to recover, but lots of people have rejuvenated tubes using methods like these. One difficulty though is once it flashes over it can destroy the grid completely and there's no recovering from that.
@@va3dxv Thank you for your comprehensive reply. Yes, as soon as I posted the comment I started thinking it could refer to what you comment and reminded me of what happens to halogen incandescent lamps if they are not powered at full specified current periodically, for example, if they are used in dimmed circuits. The filament needs to glow at high temperature for the evaporation cycle of the halogen material to happen, or something like that, jaja. Anyhow, if there are impurities it's because the manufacuting process was not optimal... although which manufacturer would have guessed that we would be still palying around with their tubes 50 to 80 years later!
I had them do a 3-1000z and it worked perfectly. 120.00$
That is good to know and a reasonable price. I have two perfect 3-1000Z but if I need to have them degassed, who and how do I get this done?
"I have to re-evaluate" LOL! Is there a difference between degassing the old/used tubes and NOS tubes that have been in storage for decades? I searched vids as I want to use some NOS 4CX300 tubes I've had for a long time. n2eye
Personally - and this is just me - some people will disagree - I just plug them in and use them. I don't have any problems and have lots of tubes, some probably older than me, and they work. Some kind of magic came up around the 3-500Z. According to Eimac, tubes have to heated right to the point of destruction to make the "getter" work and that can only be done during manufacturing. I think we should do whatever make us feel good. 🙂
Bonito
I don't know if you still have that 3-500Z, but test it again with the grid tied to the filament/cathode..... You may be surprised to get results similar to the 4-400 you were testing earlier....
What size filiment transformer u used to do this
5 volt, 30 amp
What will you do with the bad tube?
I sent it back and got my money back.
I'm not sure what to make of this. I would never, ever, tie the grids to the plate, at least without ballast, metering and very fast acting fuses. Looks like a great way to destroy the grids. If I do something like this I will likely float the grids.
Was this for evaluating or for de-gassing? For evaluating, l think this is poor way. I would expect a good tube to have almost a runaway current draw as it moves into the forward conducting mode, some ballast is definitely required. A typical way to measure tube performance is to pulse the grid with very high pulses of short duty cycle while monitoring the cathode current with an oscilloscope.
There was no degassing attempt here. To degas you would need to run the plate dissipation up to near the max ratings with a lot of cooling for a long period of time.
Thank you for setting it all up, it was interesting to watch.
I certainly respect your thoughts on this. You, like so many others, including myself, want a solution to save a these beautiful and exotic vintage gassy tubes.
In a nutshell, I have come to the conclusion, after multiple attempts, that this whole "degassing" exercise is nonsense. Getters in tubes are real but the amount of gas they are capable of absorbing is extremely small - very finite.
As a typical example of this degassing process - someone has a pair of 3-500Z tubes for their Heathkit SB-220 that have set up for two or thee years and they are concerned that they have become gassy. They have been told that gas will leak in around the filament seals. So, they go thru this smoke-and-mirrors routine of degassing them and afterwards plug them in and with great trepidation finally raise the plate voltage to nominal operating level. The tubes work... this is great... now, they are convinced that it has to have been because of the care they took in their degassing process. It is all nonsense. Maybe the special metals that the anode is made of is supposed to absorb internal gas when heated to max plate dissipation - I really can't say and I can not find where Eimac says either.
I have tried all the old-wives-tales of how to degas this tube and others over many years. I heated the plate to full 400 watts of plate dissipation for a long time with a cooling fan on it. I can't show every moment of a three hour process I went thru in a video.
As for leaving the grid floating in a high mu triode, the grid will become charged and shut the plate current off - to zero current no matter the plate voltage. The grid of any tube must have a DC path to ground even if it is multiple gig ohms otherwise the accumulated charge will bias the tube off. This is what will happen if we float the grid in any tube. By tying the grid to the plate we turn the triode into a diode. I agree there must be a ballast and that is my external Variac on the HV supply.
I tried to kindly and respectfully show that this hopeless method of saving a gassy tube could actually work. It doesn't work and it never will. It is an exercise in futility. I have many tubes of this family of glass tubes dating to the early 1960's and some even from the 1940's and I plug them in and turn them on and they work - or they don't. The vast majority work as they were made and sealed properly even 70 years ago. A tube that has become defectively gassy will not be saved with this procedure no matter how much we want it to work. I wish it did.
@@ElPasoTubeAmps Thank you for the response, it does clarify things.
As you pointed out, floating the grids does not work so I will revise my statement. To make a tube act as a diode I would tie them to the plate with 1 megaohm resistors, after all a diode is just a cathode and anode.
While the variac is essential it is not really a ballast. A light bulb(s) in series with one of the variac leads would be a good ballast.
I think you are correct that it is very unlikely to resurrect a bad tube using these sorts of methods but I don't think they are completely worthless. I used to take care of a 10kw AM transmitter that used 4CX15000 tubes. These darn tubes would like to arc over if they sat unused for a long time. When we put the transmitter in standby service the manufacturer recommended running the filaments for a day or so every month the keep the gases at a low level. This is not to say that the manufacturer was correct but they seemed to have a lot of experience with the problem. Also, I have seen an article somewhere where a number of tubes were tested for flashover voltage, and after reconditioning by running them in some manner, the flashover voltage was dramatically increased. So I think that there is some merit in carefully running up the heat in tubes that have been unused for a while.
My interest in the matter is that I have acquired a transmitter with four 4-500A tubes. These tubes are just about un-obtainable now. They were running fine when the transmitter was shut down 20 years ago and I want to bring them up without incident. I will probably run the filaments for a week and then slowly run up the plate and screen voltages with variacs and ballast lamps, slowly bring up the dissipation. I also have some 4-400Cs that I need to do the same. It's several thousand dollars in tubes so even if the process is futile it's worth my time to slowly bring them up to full operating parameters.
Thanks for doing the video, it did answer a few questions that I was thinking about.
@@radarecho57
I certainly appreciate your response and input to this subject. It can be a touchy subject with some people. Your experience with the 4CX15000 tubes is where the rubber-meets-the-road and success is hard to argue with. I have read about this tendency to flash over but I have no experience with it and if the tube manufacturer suggests something, it is probably a good idea...regardless of what us ham radio operators think.
Wow.. a transmitter with four 4-500A's - I would love it - I have no idea where I would put it but I would come up with something. :-)
I realize that my hard-nosed approach to this degassing could, in some case, be wrong but it has never worked for me. Maybe my tubes were just too-gone to be saved. There actually is, in Eimac literature, a mention that running filaments at low voltage (temperature) can "poison" the cathode by making it absorb gasses. I do not know if this applies to the family of 4-400A type tubes. There is a link to that article at the top of my video. In any case, these type of discussions with the sharing of experience is very valuable, in my opinion, and I have been extremely fortunate to run across so many knowledgeable people, like yourself, commenting on my UA-cam videos and sharing experiences. Stay safe and have fun with the big transmitter...
If you tie the grids to the plate, how do you make sure you're not exceeding the maximum grid dissipation?
Without measuring the grid current, we really wouldn't know. It is one of the "prescribed" ways of heating these tubes to maximum plate dissipation with a fairly low voltage. It turns it into a diode. I am going to guess that the plate is so dominate in size that it attracts the vast amount of current and not much current flows in the grid circuit but I don't really know. Maybe the fact that the tube still works after the procedure, assuming the tube was good in the first place, then we can assume it did not damage the grid. :-)
@@ElPasoTubeAmps I see some other commenters said the same thing. Since the grids (plural, since this is a tetrode) are between the cathode and plate, a lot of electrons will hit them if they're all at the same potential as the plate. I would also insert resistors in each grid to safely limit their current.
Is it okay to run the two different types of 3-500 Z's in the same box together or do you want to keep both tubes the same?
I don't see a problem as long as they are reasonably matched. I would observe if one is running hotter than the other under operation and if they look pretty much the same (orange hot plate) I would assume all is OK.
@@ElPasoTubeAmps well this is the reason I'm asking the one I have that is like the one you are testing does get hotter than the other one I have to watch it very carefully and make sure that I'm tuned just right
The whole idea of that kind of tube is that it works in a Vacuum, meaning that there are No free floating Gas molecules inside that tube.
Vacuum Pumps only work to a limit, so in Manufacture, they sucked out as much air as possible, after throwing in some chemicals ('getters') that will react with Oxygen, Nitrogen etc at high temperatures, then seal the tube, which Will have a little bit of air still in it.
When you First power up the heater element, those 'getter' chemicals are activated and 'get' the rest of the gasses out of the air, converting them to a Solid, which cannot easily become a Plasma, like you saw in your 'bad' tube.
I guess the only option is to drill a hole, suck out some of the air, stick in more getters, then seal the hole(s).
Do-able, but sounds like a lot of work when there are so many valves sill available, and MOSFETS work too.
From an Eimac document I read on "getters" it says that the tubes are heated, during manufacture, to almost destructive temperatures to make the getter work. I assume that is likely much hotter than running the plate at maximum dissipation and I don't know if the getter will work again after being 'fired' the first time at the factory. I truly wanted this to work and this idea floats around the ham radio communities but I think it is total nonsense and a waste of time. As I have either said or shown in some of my videos, I pull a tube out of my supply that was made in the '60's if not '50's and I plug it in and turn it on, filaments and HV - and it works. I don't go thru the smoke-and-mirror routine of "cooking" the tubes every time they have not been used for a year or so.
@@ElPasoTubeAmps Basically it's Manufacturing, so they only put enough of the 'getter' stuff in there that was required to 'get' the rest of the air out, down to the required vacuum so they could sell the Valve and have it work long enough to get past the warranty period.
NOS (New Old Stock) might have already been slowly leaking back in 1970, so Today in 2022 there just is no vacuum anymore inside that tube.
No way any amount of heating is going to 'recondition' it, because there never was enough 'getter' to clear out that much air.
It should be possible to re-condition an ancient valve by sealing up whatever leaks exist, also drilling, putting in more 'getter' chemicals and re-sealing.
Unlikely that would ever be worth the effort though.
An Old, Unused valve that has a tiny leak, also some of the getters left over (inside) definitely Can be 'reconditioned' by running just the heater for a while, like 24 hours, maybe with cooling too, maybe not (no idea)
All chemical reactions depend on a certain amount of Energy being present before they can even start to happen.
Think Gunpowder.
It does nothing at all until some flame gets in touch.
It suddenly occurred to me that this setup is identical to the circuit used by the EICO 666 (and many other testers I'm sure), except for the power supply being able to handle much larger currents.
I am beginning to see that testing larger tubes is simpler than we think if we are willing to build a test jig. Thanks for your comments.
Yeah is busted, probably as you said when the gas starts to ionize it acts like a thyratron and starts to conduct.
Just as an idea to try with a "scrap" tube like this would be to heat up the plate with an induction heater like they were doing at factories with getters, since ti is busted it would be worth a try....
I have never seen a tube tested like that, apparently it works great and i wrote it down in the appnote! i am just a little bit concerned about the grid current since they are strapped to the anode, maybe for a short period of time is ok but just something to check out next time.
Manuel - I have to ask you a personal question.
Have you ever had a tube that failed and ionized consistently like the one in my video that you actually fixed with this degassing procedure?
I don't want to know about what you have read or what you believe or have been told about from anyone or read on books or on the Internet. I want to know, one-on-one, if You have had success with this procedure. This does Not include taking a 3-500Z or whatever tube that you have had for years or decades, and doing this degassing procedure and Then plugging it in and having it work. If you do this procedure before ever testing it and then having success, it would prove nothing as it very well might have worked just as well without this procedure.
I think this procedure is folk-lore and nothing more. Nowhere, does Eimac say this will work. I know you will tell me the truth and I will accept what you tel me as the truth. Stay safe...
@@ElPasoTubeAmps no, i have not savaged any tube in this bad condition, the tube i told you about had just a little bit of glow in it while working. i agree that for this particular tube is the end, and that even in this highly technical field there are a lot of myths and people that speak even if they have no clue, i was just thinking that maybe induction heating could work just as an experiment.
@@manuelminutello3027 Thanks Manuel, yes, this tube was very nice and clear with a perfect looking filament. As for heating of the plate where this tube performed different from a good tube is, I would connect it as a diode and start raising the voltage on the output of the Variac (thru a bridge for DC) and the plate current would start rising slowly and if I kept my hand on the Variac dial I could stabilize the current at any level I wanted even up to 7A. I let it sit at 5A at 100V for a few minutes and the plate was very red (500 watts dissipated in the plate). I know, some are going to say this is impossible and now I have ruined the filament, etc. blah blah blah. I am reporting exactly what happened. OK, then I could raise the voltage a little more and the current would start to rise and as some point it would quickly soar and the tube would ionize and blow the fuse. No doubt the tube is BAD and from my bit of experimenting with it, heating the plate to very hot temperatures, it did not help. Maybe if I kept it there for several hours or days, maybe that would fix it... Now, with all that said, I do believe that running the plates orange hot (within proper limits of the tube) seems to lengthen the life of the tube. I have actually read this from an Eimac article. I also think it is good to rotate tubes so they don't lay around dormant for decades. I don't know if the plate is absorbing internal gas (gettering) or the seals are becoming more annealed or what, but I do believe that part.
Now a good tube - I could raise the voltage on a good tube (in the same test jig) and the current would rise to 1A or maybe 1.2A and it would be stable at 100 volts never rising any further. The plate would not turn red and I figured I was super-heating the cathode and from my casual observations, it seemed to make some of my used and somewhat weaker tubes have better emission because of the power I could see coming out to the dummy load when I tested the tube afterwards. I allowed the good tubes to heat for 2 minutes. The changes in power output were not under proper control and maybe my line voltage rose 3-4 volts from an air conditioner, etc. turning on or off so my observations were not properly controlled to say this really helped emission of the cathode - who knows. The interesting things about myths is they are easily created but never able to be extinguished. It is the way the world works. Thanks for your reply and honesty.
Do you have a copy of "The Care and Feeding of Power Grid Tubes" published by Eimac? If you don't, we need to get you a copy or scan of it.
Jennifer,
Yes, I do have it and I have poured over it for years. Nowadays it can be found for free in a PDF on the Internet. I think it is just time I accept that this tube is not going to be degassed. Some of my videos are dumb and are about things that most people would never try but even then, they document what does not work or maybe, what does with a twist. After making this video I went back to my amplifier and installed it again (a fool never learns...) and tried it at lower high voltage levels only to have it "crater" on me again. Other people have bad tubes that can not be "degassed" and I have one also. End of this story. The really interesting part about all of this is the Amperex 4-400A tube I dug out from the bottom of my pile. I bet I have had that tube 40 years and always considered it bad. I save bad tubes in a separate box just to use for lay-outs in equipment I am building so I don't have to risk the good ones. Look how good it measured and performed... A similar thing happened a few years back with the Penta Lab PL-175A tubes (Eimac also made a 175A) and I always considered them bad until somehow I noticed that they are actually pentodes and not tetrodes and the ring Must be grounded to ground the suppressor grid. Once I did that, they perform beautifully. Holy Cow... Life is always full of surprises. Thank you for commenting. I think we all enjoy and learn a lot from each other. PS - I still think "degassing" is BS...
@@ElPasoTubeAmps Nothing you do is "Dumb"......its just stuff the rest of us want to do but arent game to do !!
Unless I'm mistaken, I think Bill Orr (W6SAI) was the author of that document. He authored other things for them as well. I know he was an Eimac employee.
I agree this tube is dead.. So might be worth experimenting further on.. I'd try adding a 150w light bulb in series with it and run it at the 150w or so for a good few hours and see if it improves.. I doubt you'll revive it completely but if it improves at all then there's further experiments worth doing!
Use a mercury vapour ballast instead, a 125W one for 230VAC operation will be a simple choke, and will give a good current limiting in the AC side of the supply, and will not want to be a room heater, plus the reactance is generally linear. Will limit the current to 1A with a 230VAC supply, almost irrespective of the actual voltage across the tube itself.
HomeDistiller I was wondering about that, running it in flashover with a current limit. I guess it depends whether the gas will burn below the flashover point or above it: and of course if there is an actual vacuum leak you aren't plugging it, so you can't get ahead.
Hello 👋 sir...can you tell ware can i get a schematics or something to build a 3000 volt power supply for two 3-500z??? Thanks for your patience and help i really appreciate it 73
Here is a link where there are some good documented articles including power supply schematics that I hope will help you 73 WA4QGA
w2dtc.com/w2dtc-class-a-rf-amp-page.htm
@@ElPasoTubeAmps waooo this is the fastest reply i ever gotten from anyone lol . thanks 🙏 for the time stay blessed 73 p.s do you do repairs or do you have a email if i need doble check...i have so many questions lol i have about 5 amplifier and one of them used to belong to my grandpa and he was a ham operator...and is because of him i follow his lead i love the radio and everything that has to do with it ...i became ham like him ...just a bit confusing because i left it and pick it up again and i want to build a power supply i have a bigger one but this thing is humongous!!! I have some pictures but i don't know if I cud upload...but anyway thanks 73 don't want to take any more of your time I'll check them out if i have any questions can i asked for you help ....Tru here or what ever just let me know stay blessed 🙏💪 my honor sir
@@ElPasoTubeAmps ohhhh nice let me feed my brain 🧠 lol 😆
You are reaching the ionizing voltage of the gas (contaminent) ...just like in gas (zenon) or mercury vapor rectifier...Then the tube fires and the conduction increases wildly. This is how an OA2 voltage rectifier works also. Now, all tubes have a getter, which chemically bonds with oxygen to remove it from inside the envelope...so the filament doesn't burn up. But metal and other chemical contaminents can gassify....and the getter will not - cannot - do anything about them. Burning in a new old tube with filament voltage only....can heat up the getter allowing it to work again after decades on the shelf. Either it works or it doesn't. Nothing will fix a poor bond between the glass and the tube pins...so if they leak....its all over for the tube and it will burn up. You have demonstrated what tube testers (hickok) do when you run the Gas Test. This is voltage dependent....so if you could limit the current you could still demonstrate the ionization in a bad (gassy) tube. I think this is extremely useful way to test unknown tubes without risking damage to an amplifier !
You make a good point about limiting the current to test for gas. If the tube is in an amplifier there is no safe current limiting. I have tubes as far back as the 1950's, I am not going to name all the tube numbers but in almost every case when I use them, no matter how long they have been in the attic, I plug them in and turn them on. They work - if they don't, like the ones in this video, they have to go away. I know of no way to "getter" a tube that is as bad as the one in my video. It looked perfect and the filament was beautiful and bright.
I "love" my tubes and I treat them nice and let the ones like the 4CX1000A, for example, warm up per Eimac requirements using a 180NO120 delay-relay and put air vane switches on them to power them off if I lose air, etc. but the thorium based glass tubes, like a 4-400A, etc., they get 30 seconds warm up and then get the full 4 KV.
Comparing it to an 0A2 is a good idea. VR tubes have a current limiting resistor to set the resting current to something like 25 - 30 mA. In testing the big tubes including the Hg rectifiers, putting a current limiting resistor in the anode line might save some fuses and keep the drama down when throwing the switch during testing an unknown tube. 🙂 Hg rectifiers can work fine as say, 2000 VAC but arc over at 4000 VAC.
I recently read that the way they classify a 4-1000A post-production for 30KV pulse rating as a 4PR1000A to work in radar sets is they current-limit the voltage and raise it to those levels and even use it to "zap" anomalies in the tube that might make it arc in field conditions. Thanks for your comments.
I have tried various methods, none are a single answer.......I wonder if they are fired up early in their lives, it sets the seals throughout the tube to slow down gassing.......
I guess in their day when they were new off the factory floor, no one really thought they would be still in use and even in some cases brand new old stock in this age......they really have exceeded their intended working life by many decades
It is beginning to seem to me that the used Eimac tubes (and other vendors) that are 50-60 years old are much more likely to work than the truly NOS tubes that are of that age that have never been used. I have plenty, as you have seen in my videos, of excellent used tubes that are definitely 50+ years old. Until someone can tel me that they have personally fixed or witnessed a fix of a failing tube from this procedure, I will not believe it works. This does not include doing this procedure and then having their 3-500Z work in their SB-220, for example. It means having had one that failed, like mine in the video, and then going thru the procedure and have it work. I am looking for a cure, if it exists, and not a vaccine.
@@ElPasoTubeAmps lol.....me too....a true tube resurrection !! .....I am yet to say impossible, but I have a lot of dead big tubes from various jobsites, None have reemerged from the dead yet.......having said that, I am all for it if it can be done.......I never throw out the dead ones......I live in hope !!
I have a trio of RK65/5D23 tubes, all used. I did this procedure, and compared results - one tube was obviously bad, one obviously good, and the third seemed to benefit. The third tube took about an hour, pulling rated plate current, and the current kept increasing. I had to keep adjusting the plate voltage lower every few minutes until it finally levelled off, within a few volts of the good tube. Subsequent tests one month and several months later showed it to have retained its 'good' rating. Would it survive long with real HV? I don't know, and don't currently have a way to test.
lol stan at the end there i was giggling a bit, seeing myself years ago with a broomstick to flick the ht on , hehehe.... any a bad tube is a bad tube, some can be used at lower ht, some goes corona 123 :) then the milky ones are in the re too... what i learned i s too give a tube a fair chance, but when is throws gifox and carona, it becomes a door stop .
Johan zs2cx
I think you got it exactly right, Johan. This tube "might" work at lower HT but I typically run 3500 on my GG amplifiers. Thanks for your comments.
Bazuka Foz do Iguaçu pr Brasil 🇧🇷🇧🇷
i use to heather eimac and others no getter tubes one week , just filaments on, nothing else
Ok, so I have absolutely "0" experience with these larger tubes.i dont see a getter spot on them, do they have a getter?
Large transmitting tubes like these don't use getters.
I forgot to mention. These tubes run Very very hot. Especially compared to receiving tubes. The Getter can't stand these higher temps.
The getter is the zirconium coating on the anode, which needs to be heated to absorb impurities in the vacuum.
@@ntilewills5679 Yeah, they do. The zirconium coating on the anode is the getter.
(gassy tube) When the Voltage gets high enough the conduction by Ions (air component) overtakes the electron conduction, this is damaging. Try reverse applied Voltage polarity ad try with the filament cold with both polarities. Ron W4BIN
Let's talk when you have time. 73, Jim
Jim... Absolutely... I have heard you on lately and have wanted to get in contact with you.
I have just gotten my 833A amp tuned to perfection so I am really enjoying it. It delivers 1000+ watts as easy as it does 10 watts. It was a challenge getting the neutralization and grid resonate circuit tuned perfectly for good stability on such a large TGTP triode amplifier but I did it.
Many articles out there say the 833A is no good above 40M. Too many people think everything should be cathode driven GG or resistor loaded if grid driven. Got to go the full length of tuning the grid and neutralization.
I am usually on in the afternoon from maybe 2 PM to the end of the day on 20M.
You are always welcome to contact me directly at my YT email of: TheAudioShop@SBCGlobal.net 73
He shows us the "bad" tube and then bangs it on the transformer putting it down. I got a tickle out of that. :) Tod KJ6H
Is that muffin fan running?
The beginnings of air leaking 8nto the tube envelope. Gassy tube will over conduct. If you have an 8nductive heater, you can re fire the getter.
I would like to believe that and ham lore tells us all about the anode being the getter and it only works when it is orange hot. I think it is all nonsense. I can not find in any Eimac literature where it talks about the anode being the getter or about this procedure to degass tubes. Eimac does discuss the final procedure for preparation of the tube as it is heated to a temperature just below destruction which we can not do and control. I plug in tubes that are 50+ years old and haven't been heated in decades and they work. In my opinion, I just debunked the whole smoke and mirrors myth and do no waste my time "degassing" tubes. If the tube is gassy, you need another one that is good.
maybe this is a bad idea :) so true
Yes, in my opinion, a waste of time. I can never say, "never" can it help, as no one can understand every situation but in general, I believe it is just smoke-and-mirrors. People believe in four-leaf-clovers as good luck and I even like the idea of such things in life but when it comes to high voltage and the like, I tend to stick with repeatable results.
@@ElPasoTubeAmps i Have 2 4-1000a tubes that have a soft problem, (new old stock) when i put them in operation, drive = 10 watts output 0 then 4 hours later 10 in 10 out, increase drive to 50 watt output 60 watt , leave for 4 hours output 200 watt, drivge 120 watt output 800 watt.. gave up on it and fed it 250 watt input rf, output came back 6kw, was really surprised, but when i leave them in storage for a while same symptom.
Watching the HV testing again - at about 28:05 I say, "this is probably a bad idea", definitely a bad idea to have 2000 + volts open like this. I guess I am supposed to say, "Don't try this at home..."
Expensive thyratron !!! 🤣
Hi! , no not these degassing procedures, I don’t think it would work from a physics standpoint. The tube needs to be evacuated. There is a picture tube shop in Tx that can do it for you.
Please let us know the name or address of how to get this done. I don't have any tubes needing a vacuum pulled on them right now but I may in the future. Thank you...
Just for what is worth, and if I recall correctly back about 55 years ago or so, I worked for a company that used 3-500 as well as other tube in their products. I would run 3-500 unit that they called a pre conditioner for Tubes. Most of the tubes we received where new mil surplus. We had a rig that would apply low voltage to the plate. I believe to be the same set up you have except it would run 8 tubes at a time.
We would limit the plate current to 400 ma by varying the voltage. Never exceeding 400 ma. After 7 hours we would adjust the voltage to read 320ma and note the voltage. The tubes where then matched based on the voltage at 320 ma. They would be shipped or installed in Quad sets based on voltage at 320ma. We would see that over time the voltage would be reduced to maintain the 400ma. I think the power supply for each was limited to 500 ma at 50 volts. All of the tubes where Eimac. At that time I was in High school and had no clue what I was doing, sure what I am doing or what the purpose was other than to get a pay check.
That is some interesting information and I can understand some of it. The intention is to "match" the tubes. New, good, tubes can vary quite a bit - I have see it a number of times in audio amplifiers. The one that draws the most current and gets the hottest, like a 6L6GC in push-pull, just for an example, is doing the majority of the work while the other "good" tube is loafing. The one drawing all the current and doing the most work is getting very hot. In the case of a much higher power tube, like the 3-500Z, if it is in a pair, or quad as you describe, it is going to get really hot at 2500 volts on the plate in the equipment it is meant to work in. So, that is the purpose your of pre-condition the tubes.
I can buy new tubes and measure them and make a note of current, then put them in an amplifier and let them run, for maybe a week, and remeasure and they will most likely have changed. After some pre-conditioning, i.e. running in the equipment, they tend to stabilize for the life of the tube.
My first year in college, 1967, I worked for a small cable company and their distribution amplifiers were all vacuum tube and I built a re-conditioner just to simply light the filaments for a week or so - then we would test and match the tubes before having them put in the distribution amplifiers around the town. We would find bad ones after just running the filament for a week. I think it held about 20 tubes at a time. (small 9 pin tubes) Tube testers don't solve all problems, for sure, but they are useful for matching tubes and testing for obvious faults.
Thank you for you comments. I find what you added very valuable.
With all due respect, some of this de-gassing of bad tubes is just smoke and mirrors that some ham radio operators believe. I have lots of high power tubes, many from (before) the 1950's and 1960's that I just plug in and put 3500 volts on them and they work. Eimac documentation discusses activating the "getter" in their tubes and it requires a very controlled high temperature, right below the point of destruction of the tube, that is necessary to initiate the getter action.
On the other hand, if a fellow (or gal...) believes running their tubes in whatever manner makes them better and lasts longer, I don't want to discourage them. 🙂
Sorry son. The dog was rabid. Had to put him down.
LOL...
This is a very gassy tube. The gas molecules are being excited which avalanches the conduction. You cad have it evacuated and it will work ok. Shame to discard it with a good filiment and grids.
It lit up and looked perfect but you could see it did not work and this degassing routine is a bunch of nonsense in my opinion. That is why I took the time to post this video. I bought it off Ebay and got my money back for it.